NOTE: If two numbers are separated by a dash (-), they represent a range of values, with the larger value usually for the thinnest plates of the armor type.

MATERIAL - Name of armor/construction material in common use at the time by the people using it. If "AVE." is in name, then the material is the average of two or more materials of the same kind made at the same time by more than one manufacturer for the same purpose, but for which separate data either is not known or is not important since the material is used interchangeably and which manufacturer's plate is used is not known.

COUNTRY - Nation making this particular kind of armor/construction material.

COMPANY - Manufacturer of the armor/construction material.

TIME FRAME - Years that armor was manufactured or used aboard ship, as relevant.

TENSILE* - TENSILE STRENGTH. Test sample's minimum slow stretching force per unit original cross-sectional area needed to tear the sample into two separate parts, in pounds/square inch. The higher that this is, the stronger the metal is against slowly-increasing, non-impact loads.

YIELD* - YIELD STRENGTH. Test sample's minimum slow stretching force per unit original cross-sectional area needed to make the sample permanently lengthen by 2%, in pounds/ square inch. The higher that this is, the stronger the metal is against slowly-increasing, non-impact loads, but only against impact loads if the tensile strength is going up by the same percentage.

Y/T* - YIELD STRENGTH TO TENSILE STRENGTH RATIO. The closer to "1" that this value is, the less "give" the material has and more brittle the material will be if all else is equal.

% EL* - PERCENT ELONGATION. Percent by which the sample's length had increased just as it snapped in two. The larger the value, the more ductile the sample.

% RA* - PERCENT REDUCTION IN AREA. Percent of the sample's original cross-sectional area by which the narrowest point of the sample had shrunk just as it snapped in two. The larger the value, the more ductile the sample.

BRINELL - BRINELL HARDNESS NUMBER. Developed in the early 20th Century in Sweden as a measure of the resistance of a material to local deformation under a near-point stress, here a tiny tungsten (wolfram)-carbide ball under a 3,000 kg (6,614.4 lb) load (other versions of this scale exist, but this covers the largest range for hard materials). A formula for the size of the pit formed gives the Brinell Number, with wrought iron being about 100 (actually, 105 is the average) and circa 794 being as hard as the hardest pure cementite (actually, as the hardness goes above 650, the tiny ball begins to flatten out and the values give a greater difference than is actually there, while above 739 the tiny ball flattens out so badly that it cannot be used). This is only one of several competing hardness scales, but one of the most widely used, so I use it in place of such possibly more accurate hardness scales Rockwell "B" and "C" (58 RB = 105 Brinell, 22.5 RC = 100 RB = 240 Brinell (usual cross-over point where RC replaces RB for harder materials), 65 RC = 739 Brinell) or Vickers Pyramidal (97.5 RB = 20 RC = 238 Vickers = 226 Brinell (minimum RC and Vickers), 251 Vickers = 240 Brinell, and 832 Vickers = 739 Brinell). Though Brinell testing is not usually used here, a hardness of 66 RC is roughly 757 Brinell, 67 RC is roughly 775, and 68 RC (highest RC used) is roughly 794--these Brinell values would need a test ball harder than tungsten carbide to reach (diamond?). A slash (/) means "face maximum/back average" for face-hardened armors. NOTE: The hardness values given here are typical for the given plate type, usually with a range of about 20-30 up and down for a hard face and 5-10 up and down for the rest, centered on the given value.

USAGE - Portions of the ship that the material is used on and why, including restrictions to thickness used, if any.

*BACK LAYER values of these quantities usually given for face-hardened armors, except for COMPOUND ARMOR, where the numbers are estimates of the surface of the hard steel face layer (the back layer is regular homogeneous WROUGHT IRON ARMOR).

ARMOR - Metal plate used primarily to keep enemy weapon effects outside of an area of a target, sometimes also being used as part of the construction material for building that portion of the target, but in many cases just an additional layer of specially-formulated resistive material placed on top of the separate construction material. Also called "protective plating" and sometimes only designed to protect against secondary effects such as blast or fragmentation, while at other times designed to resist direct hits by the enemy weapons expected to be used against it under specified conditions (gun range and Target Angle for gun projectiles or aircraft altitude for bombs).

ARMOR-PIERCING (AP) - Projectiles designed to penetrate heavy armor (over circa half-caliber thickness) under a specified set of conditions with minimal damage, so that the projectiles will cause the maximum expected damage to the target, such as exploding as designed if it has an explosive filler. The maximum impact obliquity and plate thickness allowing this gradually increased as time went on and metallurgical expertise increased. Explosive filler, if used at all, was very small (4% or less in WWI and 3% or less in WWII) and a base fuze was used, with or without a time delay element. Naval designs usually employed an AP cap after circa 1898 to allow them to remain unshattered against contemporary face-hardened armor.

BALLISTIC LIMIT - Minimum striking velocity of a specific projectile against a specific plate under a given set of conditions (impact obliquity, etc.) that will allow the projectile to barely defeat the plate using its kinetic energy (not meaningful for projectiles that rely primarily on their explosive power to damage the plate hit), where the definition of "defeat" varies with the date, the place doing the test, the armor type, and/or where on the target it is used--"complete penetration" (U.S. "Navy" BL) or "through crack" (U.S. "Army" BL through the end of WWII) or "specified damage to a witness plate spaced a short distance behind the armor plate" (post-WWII U.S. Army BL) being the three most widely used definitions of Ballistic Limit.

BRITTLE - Failure of a material by sudden change from essentially no effect to total collapse in little or no time as the applied force goes above a threshold. Usually caused by the material having its yield and tensile strengths too close together, so that any yield at all immediately results in the unyielding portion of the sample next to the yielding portion having its burden increase past its tensile strength, snapping it apart, and starting an avalanche of failure as less and less of the object remains to try to support the entire load. If the material can "give" under the load fast enough, it can keep its net force below the tensile strength and not break or tear open until there is literally no more metal left to stop the force (soft taffy or high quality wrought iron can approximate this), which will prevent brittle behavior. Most materials have a maximum rate that a force can be applied before the object acts in a brittle manner. Brittle materials tend to have molecular bonds that cannot re-form properly once they are broken, unlike ductile (see below) materials where one molecule is considered just the same as any other and bonds break and re-form continuously as the material deforms under the applied force. Note that iron alloys are somewhat temperature sensitive and older forms, especially up to the end of WWI, tended to get brittle when the temperature dropped below the freezing point of water, though this had less effect on the tougher, Nickel-alloy steels; most post-WWI steels were much better due to the reduction in the amount of impurities in the metal and tighter quality control, so that much lower temperatures were needed to cause any increased brittleness.

COMMON - Projectiles designed for use against unarmored or relatively lightly armored targets, including aircraft and, in a few cases, submarines. May have a nose fuze and/or a base fuze, with the latter usually being used in those designs with no nose fuze and some armor-penetration capability (usually limited to about half-caliber-thick armor at most impact obliquities) and a smaller explosive charge (4% or less), called "Semi-Armor-Piercing" (SAP). Base-fuzed designs usually were very similar to armor-piercing designs, except for their 50-100% larger explosive charge and generally lighter construction. Nose-fuzed designs were of the large-filler "HIGH EXPLOSIVE/HIGH CAPACITY" (HE/HC) type (see below), with those dedicated to anti-aircraft use with time or, later, VT nose fuzes also called "AA Common." Base fuzes were always impact types ("Base Detonating" (high explosive filler) or "Base Ignition" (black powder filler)) using the inertia of a weighted firing pin thrown forward on impact, with or without an internal black powder short-delay element. A few SAP designs (British WWI 6-15" (15.2-38.1 cm) Common, Pointed, Capped (CPC) and post-WWI 8" (20.3 cm) SAPC; U.S. post-WWI 8" Mark 15 "Special" Common; and German post-1934 38cm Spgr. m. Bdz. u. K. (14.96" High Explosive Projectile with Base Fuze and AP Cap)), employed AP caps for use against the face-hardened armor of many larger warships, but most did not. Some SAP-type Common designs, such as British CPC and U.S. WWI "Bombarment" projectiles, had very large fillers (circa 10%) equal to the fillers of the lightest HE/HC designs.

CONSTRUCTION MATERIAL - Metal plate designed to support the ship portion that it is used in against normal forces due to gravity, ship motion, water pressure, equipment design, and so forth, usually without regard to protection from enemy weapon hits, though some extra-strong construction materials, such as U.S. Navy BuShips "Special Treatment Steel" (STS) or British "D"-steel, provided both.

DUCTILE - Ability to be slowly stretched and twisted without cracking, finally tearing apart along a surface at right angles to the applied force when the molecules of the object can no longer hold the object together. Ductile materials can break their inter-molecular bonds and immediately re-form new bonds with other nearby molecules with little or no loss of strength as they deform under an applied force. Slowly-applied-force equivalent of tough (see below).

FACE-HARDENED - Armor plate surface impacted by the enemy weapon is hardened to a much higher level than the back surface of the plate in an attempt to cause such damage to the weapon that it has reduced penetrating power or impaired explosive capability or, hopefully, both. The actual method of hardening (quenching after manufacture or chilling during cooling from the original liquid metal state) and the depth and shape of the hardness contour inside the plate varies considerably from plate type to plate type and sometimes from plate to plate of a single type if poor quality control occurs. Use of this kind of armor must be restricted to cases where the damage to the enemy weapon caused by the armor reduces its penetration, which is not the case at high obliquity, where a weapon that stays in one piece is more likely to ricochet completely away with minimal target damage than one whose nose is broken off and thus whose middle body and base can continue to punch through the plate even after the nose has ricochetted off. Also, face-hardened armor fails by having the armor in the projectile's path punch through the plate back where it acts as a second solid-shot-type projectile, increasing target damage; this is made worse by the fact that such a "plug" of armor can be ejected from a brittle face-hardened plate at striking velocities well below those where the projectile itself can penetrate the plate, which severely compromises the protection afforded by the plate.

HARD - Ability to resist being permanently deformed by a slowly-applied or rapidly-applied force (depending on the test used) on a small area. Very hard materials are usually also brittle and suddenly fail over a large area when the applied force exceeds the shear or tensile strength of the material.

HIGH EXPLOSIVE/HIGH CAPACITY (HE/HC) - Projectiles of the "COMMON" type (see above) that usually employed some kind of nose fuze (though most U.S. WWII HC designs could have their nose fuzes replaced aboard ship by a solid steel nose plug and used as rather weak SAP-type projectiles (see COMMON, above) relying on their impact base fuzes against unarmored or very lightly-armored targets) and that had a very large explosive filler charge (4-10%). These projectiles were not designed to penetrate armor of any significant thickness, even when using a steel nose plug at near-right-angles impact, and usually had almost no penetration capability except for the power of their explosive filler due to their nose fuze virtually always being set off by any solid metal plate impact, even when a fuze other than an impact fuze (designed to be set off when crushed against the object hit) was used--only when a non-detonating black powder booster charge and/or filler was used with a strengthened nose fuze would the delay be long enough to allow the projectile to punch through a metal plate prior to the projectile exploding and even here the nose-fuzed projectile's body was usually so thin that only a near-right-angles impact against very thin plate would allow the projectile to keep from being broken apart during the penetration (e.g., British post-WWI 6" (15.2 cm) HE used an impact nose fuze with a black powder booster and could penetrate intact up to about 1" (2.54 cm) of homogeneous armor at near-right-angles). Many kinds of nose fuzes were used: Impact ("Point Detonating" or "Direct Action"), Powder (burning black powder (gunpowder)) or Mechnical (clockwork) Time (set off on firing the gun), mid-WWII anti-aircraft Variable Time (VT mini-radar "proximity" or "influence"), U.S. Navy post-WWI Auxiliary Detonating Fuze (ADF) (a unique safety-precaution second fuze inserted under the main nose fuze, which was only armed by the spinning of the projectile after firing and was normally set off only by the main nose fuze when it went off as designed), and even pressure-sensitive underwater anti-submarine fuzes). During WWII, the U.S. ADF fuze was found to be set off after a very short delay by impact shock against plates only slightly thinner than those that set off the projectile's base fuze, limiting these HC projectiles with steel nose plugs inserted when used as base-fuzed, delay-action SAP-type Common projectiles to completely unarmored or very lightly armored targets since the ADF, like the base fuze, was not removable aboard ship.

HOMOGENEOUS - Having the same metallurgical and physical properties everywhere within and on it.

SCALING - Reduction in the ballistic limit of an armor type when all metallurgical properties of the plate and projectile, the projectile shape, the impact obliquity, projectile damage, and so forth are kept constant, but the size of both the projectile and the plate are increased by a given amount (i.e., a 3" (7.62 cm) projectile versus a 2" (5.08 cm) plate is replaced by, say, a 6" (15.2 cm) projectile and a 4" (10.16 cm) plate, both identical scale models of the first projectile and plate). Face-hardened armors have a scaling effect that increases rapidly with a decrease in the percentage thickness of the plate's unhardened back layer when the back layer goes below about 65% of the total plate thickness (due to brittle fracture of the hard face layers being a surface phenomenon, increasing only with the square of the scale, while ductile deformation and tearing of the soft back is a volume-related phenomenon which increases with the cube of the scale). The most ductile homogeneous armors only have a very tiny scale effect, but this increases as they get less and less ductile (due to reduced ability to stretch sideways to get out of the projectile's path before the armor splits apart, which is an increasing problem for the plate material near the impact center as the projectile gets wider), as measured by a decrease in the "Percent Elongation" (see page 1) from the circa 25% of the best ductile homogeneous armors, such as U.S. Navy WWII BuShips "Special Treatment Steel" (STS), to, for example, 18% Elongation for German WWII "Wotan Harte" (Wh) armor, which has a roughly 13.2% drop in the Navy BL for Wh plates when otherwise-identical projectile diameter increases from 8" (20.3 cm) to 14.96" (38 cm) against otherwise-identical plates scaled from, say, 6" to 11.22" (28.5 cm), compared to only a 1.4% drop for similar STS plates, though both plate types have virtually the same Navy BL (scale effects identical) against smaller projectiles. For homogeneous armors, the optimum ductility increases with absolute scale--due to the sideways stretch problem just mentioned, largely caused by factors such as the metal's speed of sound and crystal size that do not change with scale--and the 25% Elongation value seems to be the minimum to allow the minimum scale effects when against projectiles over 8". Relative scale effects due to a thicker or more oblique plate having a greater Navy BL at any scale also require that the plate have increased toughness for a maximum Navy BL, usually obtained by reduced hardness and increased Percent Elongation, on top of the absolute scale effects applicable to all plates. (See "SCALING" under FACTORS AFFECTING HOMOGENEOUS, DUCTILE PLATE RESISTANCE, below, for more information.)

SHEAR - Force applied like a scissors so that it all lies in a single plane without the rest of the object being involved in the resistance to that force. Very different mechanical properties from tensile forces (see below) and much more susceptible to brittle failure. Cracks form by shear between two layers of molecules and anything that can divert or spread out the forces causing the crack at its tip can stop it in its tracks. Tough metals tend to have high shear strength, but the two are not always in step with each other; non-metallic fibers, for example. Materials fail by shear when their molecules break apart along a surface that is parallel to (actually, no more than a 45^o angle to) the applied force, as opposed to ductile tearing (see above).

TENSILE - Force applied as a pull at each end of an object in a straight line so that it does not bend. In tests, the force is usually gradually applied to show both yield and tensile strengths.

TOUGH - Resistance to cracking under sudden impact loading where the metal has minimum time to adjust to the force before it breaks or tears open. Usually considered the opposite of brittle (see above). The Charpy and Izod toughness tests were developed after WWI to measure how tough a material is: They take a long sample, hold one end in a vice, put a notch or groove in the sample just above the gripping point and then hit the sample sideways just above the notch/groove with a calibrated swinging or dropping hammer so that the sample must fold sharply at the notch/groove. How hard the hammer must hit the sample before it breaks or tears at the notch/groove and the manner in which the failure occurs measures the metal's toughness--tough materials should fold virtually double before splitting in two, while brittle materials snap off like pieces of a china cup dropped on a hard floor. Toughness is dependent on temperature, where cold temperatures make the metal object more rigid and thus more brittle and shrinkage of the Iron crystals weakens the bond between them (see REFRIGERATION, below, for more details on this). The Charpy and Izod tests also give the energy needed to break the sample, which is an absolute strength parameter. I only consider toughness relative to the tensile and yield strengths of the material, where to me wrought iron is very tough (hard to crack or break) even though it can be torn apart more easily than some stronger, but more brittle, materials.

HARDENING PROCESSES:

. . . . Iron without Carbon or other alloying elements mixed in has a more-or-less fixed internal structure at room temperature and below of ferrite (see below), which is unchanged by heat treatments and is only slightly changed by using mechanical working to reshape and/or resize its crystals; most of its quality variation is caused by impurities or poor smelting practice which allows holes and cracks to form inside the metal. The same thing applies to wrought iron (see below), which has a negligible Carbon content (usually under 0.08%).

. . . . If Carbon over about 0.025% by weight is added (the maximum that ferrite can hold internally at any temperature) and mixed evenly into otherwise pure liquid Iron, things change radically. When ferrite is heated about 723^o Celsius (1333.4^o Fahrenheit), known as the Critical Temperature (which I will call the "Critical Hardening Temperature" or CHT to ensure no confusion with any other "critical" temperatures), doing it in a manner that the heat is spread evenly throughout the entire sample and all changes to the Iron have time to finish occurring ("equilibrium" conditions hold), the ferrite begins to change to another crystal called austenite (see below), which can absorb up to 2% Carbon at 1130^oC (2066^oF) in the rather large gaps at the center or boundaries of each crystal "cell." With no Carbon in the mixture, it takes a temperature of 910^oC (1670^oF) to completely change to austenite, but this drops in almost a straight line with increasing Carbon content to the CHT when the Carbon content reaches 0.8%, which is the maximum amount of Carbon austenite can hold at the lower CHT. This 0.8% remains constant for all larger amounts of Carbon. When the liquid Iron solidifies, it first forms austenite and when the hot solid austenite form of Iron cools very slowly through the the CHT it dissolves the austenite and forms into crystals of ferrite (more crystals than the austenite, if the size of the crystals are the same, since fewer Iron atoms are needed per crystal "cell" in ferrite). Ferrite has no available empty spaces in its crystals and cannot internally absorb more than about 0.025% Carbon (and this much only at the CHT)--the percentage of Carbon that can be held by ferrite steadily drops toward zero when the temperature is lowered to 648^oC (1198.4^oF) or raised to 910^oC, as the crystals contract in size as the temperature lowers or gradually dissolve and change into austenite as the temperature rises to near the 910^oC point, as mentioned above, so Carbon above 0.025%, as well as many other impurities, are either forced out of the ferrite crystals into the narrow gaps between the crystals as they grow when the temperature is lowered below 910^oC (usually new crystals grow from the boundaries of the previous form of crystal, when not being formed directly from the liquid Iron state, since these discontinuities act as crystalization nuclii or "seeds," which allows the size and shape of old austenite crystals to modify the size and shape of new ferrite crystals and vice-versa as heat treatments proceed) or, if the temperature drop is fast enough, some or all of the Carbon is trapped in the forming ferrite crystals and the intense pressure as the Iron atoms try to form into ferrite causes the trapped Carbon atoms to chemically combine with the Iron atoms to form cementite (see below)--cementite is "metastable" in that if the temperature is again raised to form austenite, it begins to break up back into austenite and Carbon (the higher the temperature, the faster this breakup happens) and the Carbon can be re-absorbed by the empty spaces in the austenite crystals. However, the Carbon may have been physically moved by the austenite-to-ferrite change and no longer be evenly spread through the metal, so narrow regions near the old ferrite crystal boundaries may have too much Carbon to absorb immediately, while other areas have almost none--if one waits long enough, however, the Carbon will slowly move (diffuse) through the hot austenite and more evenly redistribute itself due to the Brownian motion (intense vibrations) of the hot Iron and Carbon atoms, which are no longer held in place by the Iron atoms; this is the basis of the hardening technique called cementing (described below). If the austenite with Carbon is cooled rapidly through the CHT, much less Carbon has time to move out of the forming ferrite crystals and much more of it forms cementite (extremely rapid cooling of Carbon-containing austenite can form a third crystal structure called martensite (see below), but this is not formed at anywhere near the "equilibrium" conditions being discussed here), depending on the size and shape of the original austenite crystals, how much Carbon is in the mixture, and how fast the cooling occurs--other alloying elements added to Iron are primarily used to adjust the rates of change and final crystal structures to increase the ease (and/or reduce the cost) of manufacture (or even to allow some kinds of crystal structures to be created at all). Iron with Carbon between the minimum 0.025% (usually the practical minimum is set at 0.08% and any Carbon less than this is merely considered an impurity in the otherwise Carbon-free "pure" Iron) and the maximum 2% is called steel and is the most widely used and versatile form of Iron. Most of the following discussion is how to manipulate steel by heat treatments, alloying it with other elements beside Carbon, and mechanical working.

. . . . As the percentage of Carbon is increased from zero, the melting point of Iron drops rapidly in a nearly straight line from 1539^oC (2802.2^oF), nearly as high as Platinum and very expensive try to reach in a manufacturing plant, to 1130^oC (2066^oF) at very close to the 2% Carbon point, with only partial melting of the austenite occuring at temperatures above this line until a second, higher, nearly straight line of total melting occurs from 1539^oC at zero Carbon to the 1130^oC level at 4.27% Carbon, above which the melting point stays constant, at least through 5% Carbon, which is as high as we need worry about here. (Note: Iron initially has a third crystal structure called "Delta Iron" if the Carbon content is below 0.52%, but this turns into austenite when the temperature drops below 1400-1492^oC (2552-2717.6^oF), depending on the Carbon content, so it is of no significance to us.) When put on a graph with temperature increasing vertically and Carbon content increasing to the right, both linearly, this mixed liquid/solid region looks like a shark dorsal fin curving up to the left with its tip at zero Carbon and 1539^oC. When more than 4.27% Carbon is used at just above 1130^oC, the extra Carbon solidifies (precipitates) either as free Carbon (graphite, described below) and ferrite or as cementite, leaving the remaining liquid at the 4.27% Carbon level (this need not concern us any more here). When less than 4.27% Carbon exists at just above 1130^oC, down to the 2% Carbon point where solid austenite replaces all of the liquid Iron, some of the liquid will precipitate at austenite with 2% Carbon in it, again leaving some liquid with 4.27% Carbon. The amount of liquid left over in the 2-4.27% Carbon range just above 1130^oC is simply directly proportional to how far the actual Carbon content is away from the 2% solid value--if the Carbon content is, say, 3.135%, which is exactly halfway between the 2% solid austenite and 4.27% liquid Iron points, then exactly half of the Iron is liquid and half is solid 2%-Carbon-containing austenite, mixed together in random blobs and swirls. This same rule works for any fixed-temperature level within the mixed solid/liquid region. Simply note the Carbon contents at the two boundary points where this region is cut by the horizontal temperature line and any solid in the mixture will have the Carbon content of the solid austenite at that boundary at that temperature and any liquid will have the Carbon content of its boundary point. The only thing changing will be the fraction of the metal that is liquid (the rest is all solid austenite) and that is found by calculating the ratio of (how far from the solid austenite boundary the Carbon content is) over (the Carbon content difference between the two boundary points). For example, 1315.6^oC (2400^oF) is the temperature of complete melting for 2.5% Carbon, while at this same temperature, the solid austenite boundary is at about 1.15% Carbon. If you have an Iron sample at 1315.6^oC with, say, 2% Carbon in it, the solid austenite part has 1.15% Carbon, the liquid Iron part has 2.5% Carbon, and the percentage of the sample that is liquid is (100)(2-1.15)/(2.5-1.15) = 850/1.35 = 64%, with the rest solid austenite, all more-or-less randomly mixed together (the points where melting occurs are like points where crystals start: "seeds" where there is some difference from the surrounding points that makes it easier to change there).

. . . . Note again that the changes have to be made slowly enough for the material to adjust to them before an significant change occurs. In real life changes are made faster than this in most cases (time is money!), so some parts of the metal will change faster than others due to uneven heating/cooling or not enough time to allow complete diffusion or precipitation, but in many cases the rates of change are close enough to the ideal values given here to allow a good estimate as to what to expect at the end. When really fast changes are used, this is no longer true and more complex ways of diagraming the results are needed.

. . . . If the Carbon content is over 2%, the metal is called cast iron. It is made up at room temperature by ferrite, cementite, free Carbon, pearlite (described below), and/or a combination crystal of cementite and pearlite called ledeburite (see below). As with steel, if the cooling rate of the cast iron is very slow, a considerable amount of free Carbon is squeezed out of the Iron crystals into the gaps between them (forming grey cast iron made up mostly from ferrite crystals with Carbon "chips" in-between), while a more rapid cooling rate will retain more of this Carbon, creating cementite and, in turn, more ledeburite (forming white cast iron), which always contains 4.27% Carbon, essentially all in the form of cementite--this fixed 4.27% is the result of all other Iron and Carbon having already solidified out of the liquid prior to the ledeburite forming, keeping the liquid Iron at exactly 4.27% Carbon. Only this liquid at the 1130^oC point will form ledeburite as it solidifies, so the percentage of ledeburite in the final object will depend only on the amount of liquid Iron--no liquid or ledeburite at 2% Carbon (all ferrite and cementite and/or free Carbon) and 100% liquid and ledeburite at 4.27% Carbon (the amount of ledeburite formed decreases above 4.27% as the amount of external cementite increases)--minus any ferrite and free Carbon formed from the liquid due to using a very slow cooling rate--with the part of an under-4.27% Carbon cast iron that was solid austenite being formed exactly like 2% Carbon steel under the same conditions, all swirled together to complicate things.

. . . . Cast iron is usually very brittle and not as strong as steel, but its low melting point of 1130^oC allows cast iron to be rather easily liquified and poured into molds, creating many very inexpensive Iron products that would be hard to form by manipulating a solid piece of hot Iron--cast steel is also used for this reason, though it takes a higher temperature to melt it and only a rather small percentage of steel objects are made by casting. Cast iron is also a good material for handling compressive loads and damping vibrations, if they are not too violent, and this is why it has been used extensively for mounts supporting shipboard equipment from the deck. The main drawback for using cast iron or cast steel in armor is the inability to use any kind of mechanical method to alter the crystal structure after casting, since the object cast cannot be deformed, especially cast iron. As a result, the crystal structure tends to be even more coarse, irregular, and brittle than it otherwise would be, limiting further heat treatments to rather mild ones if cracking due to thermal stress is not to occur. Most cast armor is hardened directly from the molten state to prevent such stress build up (see chilling, below), but post-hardening tempering heat treatments are limited, since most cast armor is rather thick (which is one of the main reasons casting was used in the first place) and heat treating the center of thick objects is difficult even with more ductile materials. This makes the final cast steel or cast iron product even more brittle. Another point is that most post-hardening heat treatments result in at least some softening of the cast iron and even the hardest form of chilled white cast iron is too soft (well under 500 Brinell) to allow much softening if it to perform its function (it is possible to make a rather soft, ductile form of cast iron called malleable cast iron by reheating and extremely slowly cooling a white cast iron object, but this is not a process used with armor). Cast armor is only used when a somewhat lower grade product is acceptable and increased speed or reduced cost of manufacture is more important (for example, late- and post-WWII cast steel tank armor, though even here welded rolled steel armor was preferred) or there is no other way to manufacture the item (see GRUSON CHILLED CAST IRON armor, below).

"AVERAGE QUALITY" is an estimated average for all thicknesses of the material compared to U.S. Navy WWII Bureau of Ordnance Class "B" armor or WWII Bureau of Ships "Special Treatment Steel" (STS) ("Standard" Quality = 1.00). It gives a rough ratio of the minimum striking velocity needed to completely penetrate that kind of plate at right-angles ("normal" incidence) compared to the velocity needed for the Standard Armor of the same thickness under identical conditions. It is used as-is for projectiles up to 8" (20.3 cm) in diameter, but is modified using the formula under SCALING, below, for projectiles over 8" if the Percent Elongation of the plate is less than 25%.

"SCALING" as defined at the beginning of this document is assumed to be proportional to a function of the Percent Elongation determined from the German Navy's 1940 "Gunnery Bible" "G.KDos. 100" Wh armor penetration tables for similar 20.3 cm (8"), 28 cm (11"), and 38 cm (14.96") Psgr. m. K. L/4,4 ("APC Projectiles 4.4 Calibers in Total Length"; the last, best Krupp APC projectile design). This function only affects projectiles over 8" in diameter, to my knowledge, and it is an additional scaling multiplier to decrease the Navy Ballistic Limit (NBL) below that of a 25% Elongation (or larger) metal, which is assumed to always match my original STS data based on U.S. WWII Naval Proving Ground tests. The formula is:

where "D" is never less than 8" and "%EL=" is never more than 25% (if either is out of bounds, then NBL = (NBL_STS)(A.A.Q.)). For example, if the German 38 cm APC projectile is used against Wh, which has a % EL = 18 and an Armor Quality = 1.00, then the NBL = {1 - [1 - (18/25)^0.5](14.96 - 8)/8}(NBL_STS) = (0.868)(NBL_STS)--I roughly estimated an average NBL = (0.864)(NBLSTS) from the 38 cm Wh table in G. KDos. 100, which is obviously close enough to the formula result for any possible purposes.

PURE IRON (Reference)
USAGE: Laboratory specimens only.

Pure ferrite at room temperature. Pure Iron rusts easily, so it is a poor material to use in any normal environment.

AVE. WROUGHT IRON
USAGE: All naval armor and ship construction.

First ferrous construction and naval armor material. Also formed the back layer of British-developed COMPOUND face-hardened armor (see below).
AVERAGE QUALITY: Estimates: 1855 = 0.6 (French) & 0.55 (British and others), 1870 = 0.6 (all)

AVE. "MILD/MEDIUM" STEEL
USAGE: Ship construction and some early armor.

Wide range in quality. Older steels very brittle, but eventually became the high-quality material used today for most ship construction. First armor was 22" (55.88cm) vertical plates for 1876 Italian battleships manufactured by French Schneider & Co. of Gavre, which literally fell apart when hit by large projectiles, but which could shatter any of the standard chilled cast iron projectiles (German Gruson type and British Palliser type) then in use, preventing them from penetrating this armor even if the armor did break to pieces in the process. Until 1890, only Schneider & Co. had the skill to make thick steel armor plates, though a gradual improvement in expertise allowed steel to be used more and more in less demanding roles. Percent Elongation varies from a low value equal to German Wsh to a high value equal to U.S. STS, so the scaling results must be decided proportionately for each material separately.
AVERAGE QUALITY: Estimates: 1876 = 0.7, 1890 = 0.75, Post-WWI = 0.8 (when hit by projectiles up to 8", dropping off slowly and steadily when hit by projectiles above this size at a rate between German Wsh and U.S. STS, depending on material's Percent Elongation)

AVE. HIGH-TENSILE STEEL (HT/HTS)
USAGE: Ship construction, light armor, "Protective decks," and anti-torpedo bulkheads.

Later versions used more alloying elements, but only a little Nickel was used in original "recipe." Usually used in multi-layer laminates of 1-2" (2.54-5.08cm) per layer. Has a Percent Elongation equal to German Ww with similar scaling results.
AVERAGE QUALITY: Estimates: 1895 = 0.8, Post-WWI = 0.85 (when hit by projectiles up to 8", dropping off slowly and steadily when hit by projectiles above this size at a rate equal to German Ww)

GERMAN SHIPBUILDING STEELS (1890-1945)
. . SCHIFFBAUSTAHL (1890)
. . USAGE: All warships.

Schiffbaustahl III was the equivalent of British HT high-strength shipbuilding steel (see above). Used in Germany as HT steel was used in Britain, except where Krupp "LOW-%" NICKEL-STEEL (see below) was used, instead. German shipbuilders tended to use much less HT-grade steel (Schiffbaustahl III) than British shipbuilders, using regular MILD/MEDIUM STEELS (Schiffbaustahl I or II) (see above) as much as possible. "Ste. 42" and "Ste. 52" were higher-quality steels than Schiffbaustahl II and III, which they largely replaced, though not quite as strong in tensile tests, being among the strongest of the Mild/Medium Steel types, though their improved properties in all other ways more than made up for the small loss in ultimate tensile strength. These steels have Percent Elongations between German Wh and Wsh with proportionately similar scaling results.
AVERAGE QUALITY: Schbst.(1890)/Schbst. I = 0.75, Schbst. II/Ste. 42 = 0.78, & Schbst. III/Ste. 52 = 0.8 (when hit by projectiles up to 8", dropping off slowly and steadily when hit by projectiles above this size at a rate between German Wh and Wsh)

"LOW-%" NICKEL-STEEL (2 GRADES)
. . "PROTECTIVE" DECK ARMOR
. . USAGE: "Protective" decks.

Small percentage of Chromium and Nickel, but otherwise like Krupp "HIGH-%" NICKEL-STEEL armor (see below). Used in Germany for primary "Protective" decks and anti-torpedo bulkheads just as HT STEEL (see above) was used for this plating in Britain, with SCHIFFBAUSTAHL I, II, or III (see above) used elsewhere where British shipbuilders would use HT steel. Have a Percent Elongation between German Wh and Ww with proportionately similar scaling results.
AVERAGE QUALITY: DECK = 0.8 & A.T.B. = 0.85 (when hit by projectiles up to 8", dropping off slowly and steadily when hit by projectiles above this size at a rate between German Wh and Ww)

AVE. EXTRA-HIGH-STRENGTH "D" SILICON-MANGANESE HT STEELS
USAGE: Ship construction, light armor up to 2" (5.08cm), and anti-torpedo bulkheads.

Developed by British Colville Co. in 1920's as "DuCol" (British Navy "D" or "D.1" grade) low-alloy, top-grade construction steel. Widely used in British, Japanese, and Italian post-WWI warships. Germany and the U.S. did not use this material through the end of WWII, preferring full armor-grade materials (STS or "WOTAN" steels (see below)) when the usual MILD/MEDIUM STEELS or HTS (see above) were not sufficient or ballistic protection was needed. After WWII, these steels became the basis of the highest grades of the commercial shipbuilding steels. (Many WWII Russian tanks were made of this steel type due to lack of sufficient Chromium and Nickel supplies.) Has a Percent Elongation equal to German Ww with similar scaling results.
AVERAGE QUALITY: 0.9 (when hit by projectiles up to 8", dropping off slowly and steadily when hit by projectiles above this size at a rate equal to German Ww)

AVE. NICKEL-STEEL ARMOR
USAGE: All armor and armor construction support.

Up to 7% Nickel (usually circa 3%) added to otherwise standard MILD STEEL (see above) to drastically improve toughness under projectile impact. Even after being superseded by the later Chromium-Nickel-Steel armors (Krupp "HIGH-%" NICKEL-STEEL (see below) and later types), it was used as the underlying support layer for many armored areas--U.S. WWI battleship deck armor using STS (see below) originally had a bottom layer of Nickel-Steel under the one- or two-layer STS plating--and for armor-attachment bolts, nuts, and rivets to the present day. Introduction of Nickel-Steel armor in 1889 by French Schneider & Co. was the reason British-developed COMPOUND armor (a hardened Mild Steel face fused to a thick wrought iron back plate) (see below) became completely obsolete. Also, it was used as the basis of U.S.-developed HARVEYIZED NICKEL-STEEL face-hardened armor introduced in 1891 (see below). Has Percent Elongation between German Wh and Ww with proportionately similar scaling results.
AVERAGE QUALITY: 0.9 (when hit by projectiles up to 8", dropping off slowly and steadily when hit by projectiles above this size at a rate between German Wh and Ww)

"HIGH-%" NICKEL-STEEL
USAGE: Turret and conning-tower roofs and vertical light armor up to 3.2" (8cm).

Also known as "Krupp Soft" or, in Krupp's own nomenclature, "Qualitat 420 Stahl." It was the same high-quality steel used for Krupp's KC a/A face-hardened armor (see below), but without the face hardening applied. Used for full ballistic protection when highly oblique impacts were expected or plate thickness was below the minimum possible for reliable KC armor manufacture (circa 3.2" (8cm) in the WWI German Navy, but later raised to 4.1" (10.5cm) by Krupp or higher by other nations)--"LOW-%" NICKEL-STEEL (see above) was considered good enough for decks because several laminated and spaced decks and bulkheads would have to be pierced to reach the ship's "vitals" (this logic was refuted later when long-range "plunging" fire by improved projectiles with reliable delay-action fuzes became the norm after WWI). This material formed the basis of all subsequent highest-grade armor and maximum-strength construction steels for ships and armored land vehicles. Maximum thickness of this kind of armor used for heavy vertical plating was restricted due to an erroneous idea that ductile, homogeneous armor steel was always inferior to face-hardened forms of the same steel at near-right-angles impact conditions. Testing by the U.S. Navy in 1921 of thick STS (see below) and face-hardened plates showed that the face-hardened armor only had an advantage when the damage that it caused the projectile was above a certain level (shatter of uncapped projectiles was always well above this level); if not, the hard, brittle face either did nothing to help or, in many cases, actually made the armor inferior to its unhardened form. As projectiles improved, the conditions where face hardening was the preferred solution became more and more limited. In fact, the U.S. Navy retained homogeneous armor for its heaviest turret faces during WWII when they discovered that it was better than any face-hardened armor against their own virtually indestructible armor-piercing projectiles when hit nearly square-on, as would be the case for a turret pointed directly at an enemy warship (face hardening was retained for thinner cruiser turret faces because the hard face caused less of a problem in these lower thicknesses and because uncapped projectiles were more likely to be used against the ship). This original form of Chromium-Nickel-Steel used 1.75-2%, by weight, Chromium, 3-3.5% Nickel, and 0.35-0.4% Carbon. Has a Percent Elongation between Ww and Wh with proportionately similar scaling results.
AVERAGE QUALITY: 0.95 (when hit by projectiles up to 8", dropping off slowly and steadily when hit by projectiles above this size at a rate between German Wh and Ww)

"WOTAN HARTE" (Wh) ("Hardened 'Wotan' Armor Steel")
USAGE: All horizontal, sloped, and vertical armor up to 4.72" (12cm) for decks and 8.66" (22cm) for smaller areas to protect against direct hits.

Improved "HIGH-%" NICKEL-STEEL (see above) with Molybdenum added. Equal to the best non-German homogeneous armor. However, the very low Percent Elongation seems to result in a rather large scaling effect when hit by projectiles over 8" (20.3 cm), according to German "G.KDos. 100" 20.3cm, 28 cm, and 38 cm Wh armor penetration tables--verified by post-WWII tests of Wh plates up to 11.81" (30 cm) using U.S. Navy APC projectiles at the U.S. Naval Proving Ground (now Naval Surface Warfare Center), Dahlgren, Virginia.
AVERAGE QUALITY: 1.00 (when hit by projectiles up to 8", dropping off slowly and steadily when hit by projectiles above this size)

"WOTAN WEICH" (Ww) ("Soft 'Wotan' Armor Steel")
USAGE: Anti-torpedo bulkheads and some light-to-medium armor against fragments and blast.

Form of Krupp "Wotan" armor material that was especially softened in an attempt to get the enhanced strength of Wh without the reduced ductility of Wh, since maximum ductility is needed to prevent an anti-torpedo bulkhead from snapping at its joints (welds, bolt-holes, rivet-holes, the edges of bracing ribs, etc.) under the shock of a torpedo warhead or mine blast. Actual tests and wartime experience indicated that there was no significant difference between Wh and Ww when hit by underwater blast shock, possibly due to "work hardening" under the concussion stress negating the initial softness of the metal or from the fact that materials under high-speed shock-type loads do not act the same as they do when slowly stressed, as was the case of the standard metallurgical testing done at the time--Izod and Charpy toughness tests do not simulate shock waves! Also, German (and most foreign) welding practice prior to and during most of WWII was subject to "Hydrogen embrittlement" (Hydrogen nuclii in the welding rod stripped of their single electrons and migrating into cracks where they prevent bending and, thus, make the metal brittle), which compromised welds so much that the plate material used was of much less importance than it would otherwise have been. However, the low Percent Elongation would seem to result in a large scaling effect when hit by projectiles over 8" (20.3 cm) in diameter, though much less than with Wh armor.
AVERAGE QUALITY: 0.95 (when hit by projectiles up to 8", dropping off slowly and steadily when hit by projectiles above this size, but at a slower rate than with Wh)

"WOTAN STARRHEIT" (Wsh) ("Extra-Hard 'Wotan' Armor Steel")
USAGE: Armor for use against lead machine gun bullets and fragmentation up to 1.97" (5cm).

Special extra-hard form of "Wotan" armor for use on the spherical anti-aircraft directors used by WWII German heavy warships and in similar lightly-protected areas. Similar in principal to the extremely hard British and American "Homogeneous Hard" aircraft armor of thicknesses up to 0.5" (1.27cm) used to protect fighter and bomber crews, but not as extreme due to its greater thickness. Manufacture was possible because thin metal plates can be hardened (and thus strengthened) to a high level while retaining enough toughness. Similar to tank armor, which is made of higher hardness to protect against close-range, high-velocity projectile impacts, which is also true here since aircraft strafing will be at close range and projectile fragments are moving at a high velocity near the point where their filler explodes. Very low Percent Elongation should result in larger scaling effects than with Wh.
AVERAGE QUALITY: 1.10 (when hit by projectiles up to 8", dropping off slowly and steadily when hit by projectiles above this size, but at a higher rate than with Wh)

AVE. KRUPP NON-CEMENTED (KNC)
USAGE: Turret and conning tower roofs and vertical armor up to 4" (10.2cm).

British form of Krupp "HIGH-%" NICKEL-STEEL armor (see above) and used in a similar manner, though the minimum thickness of BRITISH KRUPP CEMENTED (KC) face-hardened armor (see below) was higher to make it easier to get a reliable product (face thickness was somewhat variable and the thinner the plate, the larger the effects became of any small variations). For most purposes, laminated and spaced HT steel (see above) was used instead since WWI-era projectiles usually could not penetrate very deeply into a target due to over-sensitive explosive fillers (picric acid or trinitrophenol--British "Lyddite," French "Melanite," Japanese "Shimose," etc.--being the most common of cause of this problem), non-delay fuzes, and rather poor penetration ability through thick armor, especially at oblique impact. Also formed the basis of Japanese and Italian armors of similar type. Has Percent Elongation equal to German Ww with, I assume, similar scaling results.
AVERAGE QUALITY: 0.95 (when hit by projectiles up to 8", dropping off slowly and steadily when hit by projectiles above this size at a rate equal to German Ww)

AVE. NON-CEMENTED ARMOR (NCA)
USAGE: Turret and conning tower roofs, armored decks, vertical armor under 4" (10.2cm) where "D"-steel was not used instead.

British high-Molybdenum-content naval armor directly replacing previous "KNC" (see above) (0.4% Molybdenum was used, the highest amount used by anyone and close to the highest that can be used in armor without degrading the plate's quality). Same composition as the standard British WWII face-hardened CEMENTED ARMOR (see below) without the hard face. "D"-STEEL (see above) was used extensively in plates up to 2" (5.08cm) instead of NCA to reduce costs. Normally equal to any foreign armor of its type, but quality control seems to have been lax for the thinner grades during WWII, possibly due to war-time supply problems and rushed manufacture.
AVERAGE QUALITY: 1.00 (0.9-0.95 in mid-WWII for most thin plates)

"PIASTRO OMOGENEE" (PO) ("Homogeneous Plate")
USAGE: Turret and conning tower roofs, armored decks, vertical armor under 4" (10.2cm) where British-type "D"-steel was not used instead.

Italian armor replacing WWI British Armstrong KNC armor (see above) previously used by Italy. "D"-STEEL (see above) was used extensively in plates up to 1.97" (5cm) instead of PO to reduce costs. I assume that this armor was equal to all foreign armors of this type, but I have little data. Has Percent Elongation equal to German Wsh with similar scaling results.
AVERAGE QUALITY: 1.00 (estimate, when hit by projectiles up to 8", dropping off slowly and steadily when hit by projectiles above this size at a rate equal to German Wsh)

SPECIAL TREATMENT STEEL (STS)
USAGE: Vertical hull armor under 4" (10.2cm) before 1930 and under 5" (12.7cm) thereafter; armored decks; 12-2" (30.5-5.08cm) tapered lower armor belts; and in blast- & fragment-resistant hull, decks, and vertical bulkheads.

Also known as Protective Deck Plate. U.S. Navy Bureau of Construction and Repair (later Bureau of Ships) form of Krupp "HIGH-%" NICKEL-STEEL (see above) used on all portions of a warship needing homogeneous direct impact protection armor, except gun mounts and conning towers, where the very similar U.S. Navy Bureau of Ordnance CLASS "B" armor (see below) was used. Somewhat more ductile than the average for any similar armor, even Krupp's post-WWI Ww armor (see above). Prior to 1930, armored decks using STS were of 2- or 3-ply laminated construction with STS laid above a layer of NICKEL-STEEL armor (see above). After 1930, STS was lavishly used for amidships hull construction above the waterline and as the foundation-layer for heavy armor plate of any kind, including more STS. Originally introduced by the Carnegie Steel Corporation (the largest of the three major naval armor manufacturers in the U.S. through the end of WWII, when it was called the Carnegie-Illinois Steel Corporation) for thinner armor, tests in 1921 of 13" (33cm) STS plates showed that homogeneous armor was superior to heavy face-hardened (U.S. CLASS "A" (see below)) armor when projectiles that neither armor could damage appreciably were employed (the Midvale Co., who also made high-quality armor-piercing (AP) projectiles, had just introduced its new 8-16" (20.3-40.64cm) "Midvale Unbreakable" soft-capped AP projectiles, which were virtually impervious to damage by most WWI face-hardened armors at right-angles impacts, of which the 12" (30.5cm) Mark 15 Mod 6 was used here). Equal to the best foreign armors of its type. Note that Molybdenum was never used in this armor, to my knowledge, unlike most contemporary WWII foreign manufacturers of similar Chromium-Nickel-Steel armor. Only U.S. naval armor-grade material not made by either Bethlehem or Midvale in any quantity, to my knowledge.
AVERAGE QUALITY: 1910 = 0.95, 1930 = 1.00 (the "Standard" Armor), 1941-45 = 0.95 for thin (2" (5.08cm) or less) "MOD" STS plates used only for blast and fragment protection

AVE. WWI-ERA CLASS "B" ARMOR
USAGE: Turret and conning tower roofs; gun mount, director, and conning tower armor under 4" (10.2cm).

Armor manufactured by Carnegie Steel Corp., Bethlehem Steel Corp., and the Midvale Co. was mixed together in a "crazy-quilt" arrangement, so each plate could be from any manufacturer, but homogeneous armor tended to be similar in any case (this was not true for CLASS "A" armor (see below) prior to 1930!). Rather high hardness. Equal to all foreign homogeneous armors at the time, but has a Percent Elongation equal to German Ww with similar scaling results.
AVERAGE QUALITY: 0.95 (when hit by projectiles up to 8" in diameter, dropping off slowly and steadily when hit by projectiles above this size at a rate equal to German Ww)

AVE. WWII-ERA CLASS "B" ARMOR
USAGE: Turret roofs; gun mount and director armor under 5" (12.7cm); conning towers; turret face (port) armor 16" (40.64cm) and up.

Armor still manufactured by the same three steel makers (Carnegie was now Carnegie-Illinois Steel Corp.), but now all armor of a given type was made by the same manufacturer on a given single ship, with no more mix-and-match. Significantly improved steel, but only a slight improvement in ballistic protection, since this form of armor had always had plenty of toughness (CLASS "A" armor (see below) benefitted much more from these improvements). The use of homogeneous Class "B" armor in turret faces (either as a single thick plate or as a not-quite-so-thick plate laminated to a 2" (5.08cm) Class "B" support plate) was an extension of the results of the 1921 tests of 13" (33cm) STS (see above), where the even more indestructible WWII U.S. armor-piercing projectiles made the situation even worse for Class "A" armor compared to Class "B" armor. (It turned out that most foreign projectiles were not nearly as good as U.S. designs at oblique impact, but this was not known at the time and might not have made enough of a difference in any event to alter the turret face plate material.) The thinner face plates used on U.S. cruiser turrets had less of a resistance difference between Class "A" and "B" and much more chance of being hit by uncapped projectiles that might be able to penetrate if the hard face was not there to shatter them, so Class "A" armor was retained. Also, Class "A" was retained on the sides and rear of the all turrets and on the cylindrical barbettes under the turrets, where the armor was thinner and was much more likely to be hit at a medium-to-high obliquity (30^o and up) where the face could destroy even a high-quality projectile, though at over about 55^o obliquity a ductile Class "B" armor plate would again be desirable because a ricochetting projectile might punch out a very dangerous, cork-like armor plug from a Class "A" plate, which rarely happens with good Class "B" armor, especially at high obliquity. Post-1930 U.S. warship armored conning towers used Class "B" armor so that they could bewelded, rivetted, and bolted into the surrounding superstructure to save weight--the rigid face of face-hardened armor could not be welded or drilled without weakening it or tearing itself free upon any substantial impact shock. As a result, U.S. Class "B" armor was the thickest homogeneous Krupp-type armor ever used. The Midvale Company used 0.2-0.3% Molybdenum in this armor under 15" (38.1cm) thick and Bethlehem Steel Corp. used 0.18-0.2% Carbon (the lowest amount of Carbon in any Krupp-type armor, to my knowledge), 0.3-0.4% Molybdenum, and 0.1-0.14% Vanadium (the sole use of this element in any Krupp-type armor) in plates under 7&qout; (17.78cm) thick.
AVERAGE QUALITY: 1.00 (the "Standard" Armor)

NEW VICKERS NON-CEMENTED (NVNC)
USAGE: Turret and conning tower roofs, vertical gun mount and conning tower armor under 12" (30.5cm) except where one of the CNC armors was used, armored decks other than where MNC was used, 8-3" (20.3-7.62cm) tapered lower belt armor on IJN YAMATO Class, cruiser/aircraft-carrier vertical armor except where CNC or "D"-steelwas used for light armor or fragmentation protection.

High-Carbon (0.5-0.55%) steel replacing both British Vickers KNC homogeneous armor (see above) and KC face-hardened armor (called VICKERS CEMENTED (see below) in the Japanese Navy)--in the latter case its face-hardened form was called VICKERS HARDENED (VH) (see below). The high Carbon content was the highest used by a successful homogeneous armor and equaled the highest used for any other successful face-hardened armor--pre-WWI U.S. MIDVALE NON-CEMENTED face-hardened armor (see below). This high Carbon content allowed easier heat treatments to obtain a given level of hardness, but caused the plates to be somewhat brittle, though no worse than the WWI-era armor that they replaced. This armor was kept at about the same quality level as its British-developed predecessor, making it somewhat inferior to most WWII foreign homogenous armors. Used up to 0.15% Copperto replace an equal amount of Nickel due to shortages of Nickel in Japan. Has a Percent Elongation between German Wh and Ww, with proportionately similar scaling results.
AVERAGE QUALITY: 0.95 (when hit by projectiles up to 8", dropping off slowly and steadily when hit by projectiles above this size at a rate between German Wh and Ww)

MOLYBDENUM NON-CEMENTED (MNC; not to be confused with U.S. pre-WWI MIDVALE NON-CEMENTED face-hardened armor (see below))
USAGE: Used exclusively for the main deck armor of the WWII IJN YAMATO Class battleships.

Replaced NVNC (see above) only in this single purpose; NVNC was used everywhere else in the IJN YAMATO Class. Only slightly better than NVNC, it is not obvious whether this armor, which used 0.3-0.42% Molybdenum and a more conventional 0.35-0.42% Carbon, was a copy of British NCA or German Wh (see above)--one source says that it was based on German armor--or a completely original Japanese product. Production plates were mostly in the thickness range of 7.87-9.06" (20-23cm), though a huge 14.96" (38cm) thick MNC grating plate with many cylindrical holes was placed over the openings of the funnel uptakes in the armored deck to keep out projectiles; from U.S. tests, this plate would only be about 40% as resistant as a solid plate, so the effective thickness of it is only about 6" (15.2cm) of solid MNC armor (a large, inclined, several-deck-high, 1.97" (5cm) CNC plate was wrapped around most of the lower portion of the funnel above the grating, so there was less likelihood of a direct bomb hit and the CNC plate would add some small additional protection to the grating against projectiles hitting at high obliquity). As with NVNC and VH, 0.15% Copper was substituted for that amount of the strategic material Nickel as a conservation measure. Has a slightly low Percent Elongation, between German Ww and U.S. STS, with proportionately lower scaling results.
AVERAGE QUALITY: 0.97 (when hit by projectiles up to 8", dropping off slowly and steadily when hit by projectiles above this size at a rate between German Ww and U.S. STS)

COPPER NON-CEMENTED (CNC, CNC1, & CNC2)
USAGE: All places where a full-armor-grade material was required in plates up to 3" (7.62cm) thick (CNC) or 3.21" (8.15cm) (CNC1 and CNC2), if British-type "D"-steel was not acceptable.

Nickel was in relatively short supply in Japan and a major attempt was made to reduce the amount of it in all high-grade armor. A small amount of Copper could be substituted for Nickel in the heavier plates--up to 0.15% of Nickel could be so replaced, but no more since the loss in toughness was unacceptable. However, for plates below 3" thick, it was found that Copper could replace more Nickel, up to 0.85%, in an NVNC-type plate, renamed CNC, without lowering toughness below the minimum specification level because thin plates had more inherent toughness due to various scaling effects (German Wsh (see above) and British/U.S. "Homogeneous Hard" aircraft armor are examples of this). In the later CNC1 and CNC2 grades introduced in WWII, up to 0.25% Molybdenum was added and a similar percentage of Chromium deleted, allowing plates up to 3.21" to be used with the reduced Nickel content of CNC. CNC development was thus a moderately successful effort, as much more thin armor was used (thick armor was usually restricted to battleships). Until WWII, when combined U.S./British efforts resulted in breakthroughs in low-alloy construction steels (rarely applied to armor, though), this was the only successful attempt at strategic material conservation. Has a Percent Elongation the same as German Ww with similar scaling results.
AVERAGE QUALITY: 0.95 (when hit by projectiles up to 8", dropping off slowly and steadily when hit by projectiles above this size at a rate equal to German Ww)

*******************************************************************************************************************************************************

The following information is used in my computer program FACEHARD to calculate the armor-dependent portion of the penetration process (projectile data not given here also needed):

. . "AVERAGE QUALITY" is an estimated average for all thicknesses of the material compared to U.S. Navy WWII Bureau of Ordnance Class "A" armor ("Standard" Quality = 1.00). It gives a rough ratio of the minimum striking velocity needed to completely penetrate that kind of plate at right-angles ("normal" incidence) compared to the velocity needed for the Standard Armor of the same thickness under identical conditions. There are two kind of quality: "Q" for plate strength and "QD" for its ability to damage projectiles (QD is always equal to or less than Q for all armors that I know of), both usually affecting penetration when damage occurs; if not, QD is ignored.

. . BACK LAYER THICKNESS ("BLT") is the percentage of the plate's total thickness that is not hardened in any way (not part of the chill). This factor modifies the plate's resistance because the thicker this is, the thinner the chill, and the less effect scaling has on penetration.

. . THIN CHILL ("TC") of "Y" (for YES) means that the plate does not have a significant decrementally-hardened deep face layer and has less chance of causing damage to steel armor-piercing projectiles or causes somewhat less damage when it does damage them. These plates cannot use damage to help them resist penetration as well as other face-hardened plates.

. . CARTWHEEL ("CW") of "Y" means that the plate type is excessively brittle and has extra-large armor plugs punched out of its back when holed or completely penetrated--called cartwheels by the U.S. Navy and discs by the British Navy. Plates doing this are usually of poor quality, though projectile design must be considered when assessing this.

. . SOFTSHAT ("SS") of "Y" means that the plate is of superior damage-causing ability and is able to shatter armor-piercing projectiles with soft AP caps under all circumstances, not just at over 15^o obliquity (over 15^o obliquity soft AP caps only sometimes work and they never work at over 20^o obliquity), as all face-hardened plates, except Compound plates, can do. Compound plates can never shatter steel armor-piercing naval gun projectiles, with only soft-capped chilled cast iron projectiles following the 15^o obliquity maximum. Note that the term shatter means a form of shock- or pressure-induced projectile damage on the plate surface that reduces normal impact penetration drastically and which hard AP caps always prevent.

GRUSON CHILLED CAST IRON
USAGE: Vertical armor for dome-shaped heavy gun turrets used in land and coast defense forts.

The armor was cast and hardened simultaneously in crescent-shaped wedges, widest and thickest in the middle where they were vertical and narrowest and thinnest at the top and bottom edges where they curved back to about 60-70^o from the vertical. The wedges were soldered together with zinc-based low-temperature solder to form wedding-band-shaped rings with a curved profile that had a smaller diameter at the top and bottom edges than at the side midpoint. The upper edge was grooved to seat a shallow, dome-shaped, flush-fitting wrought iron protective roof of at least 3" (7.62cm) thickness and the lower edge was sunk into a flattened-cone-shaped concrete glacis completely surrounding the turret. Two adjacent oval gun ports were formed into the heaviest wedges for the turrets, which could be mechanically rotated to train in any direction. They used guns from 5.9" (15cm) to over 11" (28cm). The hardened face (chill) was roughly 33-55% of the plate thickness: 33% in 33.07" (84cm) plates--the thickest solid armor ever used, to my knowledge--for the gun port plates of large coast defense forts and increased linearly (estimate) to 55% for plates 15.75" (40cm) thick, being a constant 55% for thinner plates down to the thinnest plates of this type made, 7.87" (20cm)--the side and rear armor of most turrets was half the gun port plate thickness and most land forts with the smaller guns used a 15.75" gun port thickness. This face was formed by using the chilling process directly from the liquid metal to hardened white cast iron, while the rest of the plate was formed using the standard sand mold to form slow-cooled grey cast iron, with a gradual change from one to the other. The chill depths are estimated from (1) a description of a land fort plate made by a visitor to the Gruson factory, (2) the fact that this form of hardening does not have the ability to control the rate of cooling with as much precision as heating a solid plate in a furnace and then quenching it, and (3) trying to cool the chill too fast would result in the brittle cast iron cracking or even breaking apart due to thermal stresses. Gruson armor was of the highest quality even though cast iron was normally quite brittle and it could shatter even the best steel projectiles of the period without any significant damage, even when hit in the same spot many times. Though not used aboard ship (no flat plates were possible), this armor later formed the basis of KRUPP CEMENTED (KC) armors (see below) after Herr Krupp bought Herr Gruson's factory to learn his secrets.
ARMOR QUALITY: Q=0.7 and QD=Q BLT: See discussion above. TC=N CW=Y SS=N

"COMPOUND" HARD-STEEL-FACED WROUGHT IRON
USAGE: Heavy vertical armor.

British answer to French Schneider & Co. solid homogeneous MILD STEEL armor (see above) that had been introduced in 1876. At the time only the French company could make any Mild Steel armor at all--22" (55.88cm) plates were made in 1876--and even they had severe breakage and brittle behavior problems that were only accepted because the steel armor could stop projectiles that wrought iron could not. The British, who could not allow the French to eclipse them and who just had their vaunted new "100-Ton Gun" defeated by the 22" French armor (the plates disintegrated in the process, but the gun could not pierce the French Mild Steel), decided to get the advantages of thick Mild Steel without as many of the brittleness problems. They made a regular wrought iron plate and a thinner 1%-Carbon Mild Steel plate, glued them together with liquid steel, heated them red-hot and rolled them into a single plate with 67-75% of the plate's thickness being the wrought iron back, and then heated the entire plate above the austenite-forming temperature and quenched it cold. The Mild Steel face hardened at its surface to an estimated 400 Brinell (probably dropping down to circa 200 Brinell at its back where it joined the wrought iron plate), while the wrought iron plate was not changed by this heat treatment. Later Compound plates were fused together more tightly by using the wrought iron plate as the bottom of the mold for pouring the steel face, so that they fused together from the start. The Compound plate's hard steel surface caused much more damage to any of the projectiles then used than homogeneous Mild Steel armor did and this compensated for the weaker wrought iron and brittle steel face, as well as the fact that plain Mild Steel has never been very tough under impact shock (it is primarily a construction steel, not armor) and such all-steel plates of the period tended to break apart and not always stop the better steel projectiles. However, this complete reliance on poor projectile quality eventually killed Compound armor when Schneider & Co. introduced NICKEL-STEEL armor (see above) in 1889 and tests by the U.S. Navy at Annapolis, Maryland, in 1890 showed the absolute superiority of the new extra-tough French Nickel-Steel armor and of improved, tougher Mild Steel armor against the high-quality steel projectiles used in the test. Compound armor was made under license by all nations except France at the time, since making it was easier than solid Mild Steel and, until Nickel-Steel and good steel projectiles arrived, just about as good. Compound armor cannot shatter any steel projectiles, capped or not, though other forms of damage can still occur. Only naval armor made from two separate, but permanently bonded, plates (though some WWII light face-hardened armor for armored cars and so forth was bonded from two plates: steel-faced steel or steel-faced aluminum).
ARMOR QUALITY: Q=0.75 and QD=0.6 BLT: 70 (average) TC=N CW=N SS=N

AVE. HARVEYIZED MILD STEEL
USAGE: Vertical armor 6" (15.2cm) and thicker.

Mr. H.A. Harvey of New Jersey, U.S.A., was the first to develop an all-steel, single-plate, face-hardened armor, originally made from homogeneous Nickel-Steel armor (see "AVE. HARVEYIZED NICKEL-STEEL" below for details), but later also successfully applied to less expensive, though weaker, Mild Steel armor by some manufacturers during the 1890's. Both forms of armor were the first unqualified successes of face-hardened armor in warships, since British COMPOUND armor (see above) never completely proved itself superior to French solid homogeneous MILD STEEL armor (see above). The fixed total face thickness of 1" (2.54 cm) means a variable face thickness, but the minimum plate thickness of this type ever used was about 6", to my knowledge, so the face was so thin that this does not matter much.
ARMOR QUALITY: Q=0.78 and QD=0.7 BLT: 85 (average) TC=Y CW=N SS=N

AVE. HARVEYIZED NICKEL-STEEL
USAGE: Vertical armor 6" (15.2cm) and thicker.

Prior to applying his HARVEYIZING (cementing) process to MILD STEEL plates (see above), Mr. H.A. Harvey of New Jersey, U.S.A., applied it to the superior NICKEL-STEEL armor (see above) just introduced in 1889 by Schneider & Co. of France. In fact, the first plate Harvey used for his perfected process was a 10.6" (27cm) Schneider & Co. Nickel-Steel plate "Harveyized" at the U.S. Navy's Washington Navy Yard in 1890. The superior performance of GRUSON CHILLED CAST IRON armor (see above) was due to its very hard face shattering the projectile on its surface, prior to the projectile doing any significant damage to the plate. Mr. Harvey reasoned that steel was stronger than cast iron so that the deep face was not as important as making the surface as hard as possible, even if the hard region was very thin--once the projectile nose shattered, penetration ability dropped precipitously. (He was not quite correct in this, as later, deep-faced KRUPP CEMENTED (KC) armor (see below) demonstrated.) To accomplish this, Harvey adopted the old "cementation" process followed by hardening heat treatment ending in a water quench to form a super-hard, very-high-Carbon surface layer about 1" (2.54cm) thick after first annealing and mechanically treating the plate to optimize its properties and shape it. The much lower Carbon content in the rest of the plate and restricting the heating and quenching to just the surface of the plate face resulted in only a slight increase in the plate's general hardness and brittleness. It was obvious to him that the best steel available, French Nickel-Steel, would give the best results when cemented using his new process. This proved to be true and Harveyized Nickel-Steel armor became the armor of choice for vertical protection by all nations during most of the 1890's, being only gradually replaced by the superior, but much more expensive, KC armor in the late 1890's. However, it was the introduction of soft-capped armor-piercing projectiles during this time frame that was the major deciding factor, since KC was significantly superior against them because its deep face could cause considerable penetration-reducing damage to the projectile in addition to shatter--shatter gave all face-hardened armor types an effective bonus of a 30% increase in effective plate thickness at a right-angles impact when it occurred--so KC armor could reduce penetration whether or not shatter occurred well beyond any merely Harveyized armor type. The fixed total face thickness of 1" (2.54 cm) means a variable face thickness, but the minimum plate thickness of this type ever used was about 6", to my knowledge, so the face was so thin that this does not matter much. An interesting point of law occurred in the U.S. concerning this armor: In 1892 Mr. Harvey formed the Harvey Steel Company to manufacture his patented (U.S. Patent Number 460,262) armor and signed a contract with the U.S. Navy for manufacture of his new armor by his company or, under licence with royalties to be paid, by other companies for the U.S. Navy--he also licensed the manufacture by several foreign firms. Several U.S. warships were constructed using his armor during the 1890's, but the U.S. Navy refused to pay him his royalties for the armor because the improved manufacturing techniques used differed slightly from those given in his patent. He took the U.S. Government to court and on January 16, 1905, the U.S. Supreme Court unanimously stated in "U.S. VERSUS HARVEY STEEL CO, 196 U.S. 310 (1905)," in effect, that Harvey Armor was Harvey Armor, regardless of nit-picking details, awarding Mr. Harvey his royalties.
ARMOR QUALITY: Q=0.805 and QD=0.75 BLT: 85 (average) TC=Y CW=N SS=N

AVE. ORIGINAL KRUPP CEMENTED (KC a/A and original non-German KC)
USAGE: Vertical armor 3.2&qout; (8cm) and up for Krupp and Witkowitzer; 4" (10.2cm) elsewhere.

Renamed "KC a/A" ("KC Old Type") by the German Navy after KC n/A (see below) was introduced, this armor was developed by Friedrich Krupp of Essen, Germany, using Herr Gruson's process for making GRUSON CHILLED CAST IRON armor (see above). It was one of the first non-French major strides in steel-making and it became the basis for virtually all later steel face-hardened or homogeneous armors. It combined the Harvey "cementing" process (see above) for a thin, super-hard face to shatter projectile noses with a deep Gruson-Chilled-Cast-Iron-type face to smash the rest of the projectile afterwards (the cemented layer was destroyed along with the projectile's nose and did not help in any other projectile damage). When added to the improved steel quality due to the combination of Chromium and Nickel working together to toughen and evenly harden the plate, this deep-face bonus ranged from 10-20% of effective plate thickness increase beyond that of a Harveyized Nickel-Steel plate if the projectile shattered to an even better bonus of 13-26% if it did not shatter (i.e., capped projectiles when the AP cap worked)--shatter gave a 30% plate thickness increase bonus at right-angles impact to all face-hardened armors when it occurred, but thin-faced Harveyized armor caused much less projectile damage of any other kind than deep-faced KC armor, especially when shatter did not occur. Krupp changed the cementing process to use a continuous blast of methane ("illuminating") gas against the plate face in an air-tight oven, but few other manufacturers ever changed from the original Harvey method. As with thick Gruson armor, a back of 65-67% of the plate's thickness was used, made here of unhardened, extremely tough steel, which acted as a buttress and shock absorber to keep the plate from breaking during the period when it was demolishing the projectile. The combination of Nickel and Chromium alloy had a multiplicative effect that was better at toughening and hardening the plate than either element alone (see "HIGH-%" NICKEL-STEEL, above), so that a higher hardness could be tolerated and the Chromium allowed hardening entirely through the plate to any level from 190 Brinell (minimum possible with this metal type) to about 540 Brinell (highest possible with the Carbon content used) and to various values in-between, which was not possible with Nickel by itself. The drop in hardness from the face surface to the boundary with the soft back had to be carefully controlled to keep the face from breaking (spalling) off of the back at the boundary (a major shortcoming of Compound armor (see above) due to the abrupt change in hardness at the steel/wrought iron boundary)--loss of the cemented layer had little effect on plate resistance, since it had done its job (or failed) before the rest of the plate began to resist the projectile, but loss of an appreciable part of the deep face radically reduced the plate's resistance (this is the major cause of the improvements in projectile penetration when hard armor-piercing caps replaced soft caps gradually after 1911, since the hard caps could gouge a pit in the plate face as they were destroyed, rather than just flattening out like a soft clay ring on the plate surface). By simply heating the face surface evenly to well above the austenite-forming temperature and keeping the back surface below it, carefully controlling both surface temperatures, and then timing how long the plate was allowed to "soak" in this condition, the critical austenite-forming temperature point would slowly move into the plate and the plate's inner temperature at any point could be controlled, allowing a deep decrementally hardened chill of practically any desired depth, as well as many possible hardness patterns in the hard face and transition layers (the latter, if it exists, usually softens much more rapidly than the hard face layer) to allow "tuning" the armor to what the manufacturer thought was optimum (rightly or wrongly). If the surface was first cemented, as in most of these face-hardened armors, the result was a thin super-hard (600-700 Brinell maximum) Harvey-like layer, backed by a 500-Brinell-or-so maximum hard face layer that softened as one went deeper into the plate in one of many possible ways (different manufacturers changed this considerably over the years), ultimately reaching the 200-240 Brinell back layer hardness in one or more steps or gradual drops (the last one being the transition layer). KC a/A itself had a total chill depth of 33-35% of the plate (as in the thickest Gruson Chilled Cast Iron armor), of which the first circa 20% was "undrillable" chill (including the cemented layer), with the maximum circa 650-700 Brinell hardness at the face surface and with constant drop in hardness with depth behind the cemented layer from circa 500 Brinell to circa 350 Brinell, and then a transition layer of 13-15% of the plate that smoothly connected the back of the high-hardness portion of the chill to the ductile back in a ski-slope (no abrupt change anywhere). KC was more expensive than Harveyized armor due to the use of Chromium in its alloy and due to the necessity of introducing and perfecting the deep-face hardening process that KC armor required (special handling equipment and furnaces had to be used that were not necessary for Harveyized plates). Krupp did a much better job than most other manufacturers in toughening the back layer of its plates, as is obvious in the very good ductility when tested by the British after WWI in numerous firing trials against the surrendered battleship BADEN, but due to excessive conservatism, Krupp never changed from testing its plates with uncapped projectiles (no capped projectiles existed when KC a/A was originally developed in 1894), so Krupp never understood the need to also toughen the face of the plate to delay face damage as long as possible, which was necessary to get the best results against capped projectiles, which did not shatter instantly on the surface as uncapped projectiles did--the improved AUSTRO-HUNGARIAN WITKOWITZER KC armor (see below) shows what Krupp could have accomplished if proper testing against the actual threat (capped projectiles) had been done systematically and KC a/A armor modified to optimize it for those projectiles. The post-WWI statements that British armor was better than German armor was true for KC a/A, though not true for any other kind of German armor. The drastic improvements that led to WWII KC n/A show that Krupp had no technical reason for this inferiority and could improve its armor when it was forced to admit inferiority. Krupp and Witkowitzer made KC down to 3.2", but most other manufacturers needed more slack, so they raised the minimum to 4" (10.2cm) or greater. After WWI, Krupp also realized that improved homogeneous armor was better than KC in such low thicknesses due to its greater toughness (see "WOTAN STARRHEIT" (Wsh), above), so Krupp used a 3.94" (10cm) minimum for its new KC n/A armor.
ARMOR QUALITY: Q=0.828 and QD=Q BLT: 65 TC=N CW=N SS=N

KRUPP CEMENTED 'NEW TYPE' (KC n/A)
USAGE: Vertical armor over 3.94" (10cm) on new ships with guns larger than 8" (20.3cm).

Krupp added Molybdenum to improve ease of manufacturing; greatly increased the metal's cleanliness (general improvement in metallurgical skill by most nations); increased the steel'stoughness considerably so it could now shatter soft-capped projectiles used by most nations in WWI (Germany and Austro-Hungary used hard AP caps, as, after the projectile improvements due to the Battle of Jutland, did Britain); increased the average back hardness; increased the face thickness slightly to 41% of the plate; changed the hardness contour so that the hardness dropped in virtually a straight line from the back of the cemented layer to the joint of the face with the unhardened back (no separate transition layer), which significantly decreased the average hardness of the face layer compared to the older KC a/A armor (see above), even though the surface hardness was the highest of all face-hardened armors; and increased the minimum thickness from 3.2" (8cm) to about 3.94" (10cm). As with KC a/A, the surface of the face was kept as hard as possible, without the small dip due to tempering that other foreign armor's had, though tempering was used quite effectively in these improved plates--tempered plates were usually hardest at about 0.25-0.5" (0.635-1.27cm) beneath the face's surface, so Krupp must have done a lot of work to prevent this surface softening. (Krupp was a great believer in tradition. In fact, interviews with Krupp personnel just after WWII by the British revealed the fact that Krupp had discovered that non-cemented face-hardened armor was at least as good as cemented face-hardened armor when hit by projectiles with thick, highly-hardened AP caps, which destroy the thin cemented layer well before the projectile nose gets anywhere near the plate surface (see VICKERS HARDENED NON-CEMENTED (VH), below), but continued to cement their KC n/A armor due to tradition! Talk about reactionary!) Molybdenum content reduced from 0.4% for thin plates to under 0.3% for thick plates in steps, rather than a single amount for all plates, as British and Japanese manufacturers used. First used as 5.91" (15cm) turret face plates on the KM DEUTSCHLAND Class pocket battleships, though the "recipe" was modified somewhat when the thicker armor used in the later KM SCHARNHORST and KM BISMARCK Class ships was introduced. The armor was equal to the best ever made, well above KC a/A in quality.
ARMOR QUALITY: Q=1.00 and QD=Q BLT: 59 TC=N CW=N SS=Y

IMPROVED AUSTRO-HUNGARIAN WITKOWITZER KC
USAGE: Vertical armor 3.2" (8cm) and up.

Witkowitzer originally made a KC armor identical to Krupp KC a/A (see above), but some time prior to 1911, when it made the armor for the Austro-Hungarian battleships of the KuK TEGETTHOFF Class, up to 11" (28cm) thick, Witkowitzer changed its method of armor manufacture and ended up with the best WWI-era KC-type armor that I know of, based on actual test results using Austro-Hungarian Skoda hard-capped armor-piercing projectiles similar to the latest German Krupp "30.5cm Psgr.m.K. L/3,4" (12" Armor-Piercing Shell with AP Cap of Total Length of 3.4 Calibers (projectile diameters)) armor-piercing projectiles. The chemical composition of the plates is essentially identical to standard Krupp KC a/A, so the hardening process used must have been improved, probably by employing a good post-hardening tempering treatment, since Witkowitzer did test its plates with capped armor-piercing projectiles and would have quickly found what everyone but Krupp did: The toughness of the face needs to be increased to get optimum performance from a KC-type plate against capped projectiles. Also, as with Krupp's own KC a/A armor, the back layer of the Witkowitzer KC-type armor was probably tougher than most other KC-type armors and allowed an even better toughening treatment of the face. Just adding a face temper did not improve any other WWI-era KC-type armor as much as the Witkowitzer armor, so a combination of improved face and back treatments must have been employed, including a toughening process combined with a good post-hardening temper that prevented the face layer from prematurely cracking under initial impact shock. This is the first completely successful "SOFTSHAT"=YES armor, in my estimation, since contemporary U.S. MIDVALE NON-CEMENTED CLASS "A" armor (see below), which could also shatter soft-capped projectiles at all times due to the great thickness of its hard face, had the drawbacks of a large scaling effect rendering it inferior against large projectiles and inferior performance against any size hard-capped projectiles when tested during WWII.
ARMOR QUALITY: Q=0.947 and QD=Q BLT: 65 TC=N CW=N SS=Y

AVE. BRITISH WWI-ERA KC
USAGE: Vertical battleship armor over 4" (10.2cm).

Modified versions of Krupp KC a/A (see above) as made by British Armstrong, Vickers, Brown, etc. Somewhat softer face and back than KC a/A. Curved plates were found to be ratherbrittle when hit by non-penetrating German projectiles at high obliquity in WWI (this was not true of Krupp's KC a/A armor, as post-WWI British tests on BADEN proved). Slightly better than KC a/A at normal obliquity due to introduction of post-hardening temper to reduce face brittleness, which I have found is very important to optimum quality in a face-hardened plate, even more than steel quality or back layer hardness (within reason, of course)--Krupp kept testing KC a/A with uncapped projectiles through the end of WWI and never recognized the importance of a tough face when a capped projectile failed to shatter instantly on impact, as an uncapped projectile always did. Japanese VC first made in Japan under license from the British Vickers Company for the IJN HARUNA, IJN HIEI, and IJN KIRISHIMA, the Japanese-built sister ships of the British-built battle-cruiser IJN KONGO completed in 1912. There was a distinct improvement in toughness in these armors circa 1911, giving a small quality increase and a large reduction in the brittleness of the plate as indicated by the throwing of cartwheels in the earlier armors (curved plate hits mentioned above, for example) and no longer doing this in the later plates of these same armors.
Up through the end of 1910: . ARMOR QUALITY: Q=0.828 and QD=Q BLT: 65 TC=N CW=Y SS=N
1911-1936:. . . . . . . . . . . . . . . ARMOR QUALITY: Q=0.850 and QD=Q BLT: 65 TC=N CW=N SS=N

BRITISH CEMENTED ARMOR (CA)
USAGE: Vertical battleship armor over 4" (10.2cm).

Greatly improved KC-type armor. Thinnest--only 15% hard face plus a 15% transition layer--and softest (only 600 Brinell) cemented layer of any cemented face-hardened armor, which made this armor the best of all known face-hardened armors in heavy, battleship-grade thicknesses. Employed all of the metallurgical improvements mentioned for KC n/A (see above), including use of Molybdenum, but here in the maximum possible quantity (0.4%) for all plates. Highest back tensile strength of any face-hardened armor.
ARMOR QUALITY: Q=1.00 and QD=Q BLT: 70 TC=N CW=N SS=Y

ITALIAN WWII KRUPP CEMENTED
USAGE: Vertical armor over 4" (10.2cm).

Italian improvement of WWI KC. Somewhat lower yield strength than any other improved WWII-era KC. I assume it still used a 35% face thickness and was equal to other WWII-era KC-type armors. First used on reconstructed WWI battleships. Also used for thick vertical armor on new ZARA-Class heavy cruisers (rare outside U.S. Navy). (I use the default plate parameters given in the NOTE, below, due to having little data on this armor.)
ARMOR QUALITY: Q=1.00 and QD=Q BLT: 65 TC=N CW=N SS=Y (Estimated)

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I assume the following default parameters for all face-hardened armors that I do not give separate data for that were introduced prior to 1922, no matter how many years after this they were made (VC, for example, was never improved over its original circa-1911 version):

For new face-hardened armors introduced in 1922 or afterwards that I do not cover below, such as French KC-type armor, assume the following default parameters apply:

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VICKERS HARDENED NON-CEMENTED FACE-HARDENED ARMOR (VH)
USAGE: Vertical armor over 11" (28cm) only on the IJN YAMATO Class.

Highly modified form of VICKERS CEMENTED (VC) armor (see above). Used VC deep-hardening process, but increased Carbon content to 0.5-0.55% and eliminated cementing to reduce cost so that the maximum face hardness was about 510-520 Brinell with standard heavy production plates (some experimental plates differed, as will be discussed below). Same metallurgical composition as NEW VICKERS NON-CEMENTED homogeneous armor (see above). This armor was unusual in that it had a 7% plate thickness layer at and just behind the plate face surface that was similar to the cemented layer of non-German KC plates, in that the hardness went from circa 450-480 Brinell at the surface (where the Carbon content also decreased due to the effects of the post-hardening temper used), increased steadily to the maximum hardness at the back (inside) edge of this region (rather deeper into the plate than with cemented armor and, of course, much softer). At this point, the hardness rapidly dropped in roughly a straight line or a "ski-slope" to the minimum face layer hardness of 350-370 Brinell (about 20 Brinell hardness points above VC) at about 18-23% of the plate's thickness from the face surface, and finally dropped more rapidly in the transition layer in another, steeper ski-slope to the back layer's usual hardness of 200-210 Brinell at the 35% plate thickness point, which is the same as in VC armor. Minimum production armor thickness raised to over 11" (28cm) since that was the thinnest vertical armor used in the YAMATO Class ships and maximum thickness was 26" (66cm) for turret face plates. By retaining the old Vickers water/oil quenching process on plates well above the thickness it was designed for, all VH plates in the thickness range 17-26" (43.2-66cm) did not cool fast enough deep inside and formed brittle upper bainite at their centers, which did not make them less effective as armor, but did cause them to snap in two through the impact point on any solid hit, which could result in secondary effects such as jamming turrets (the Japanese investigated the problem and solved it, but by that time no more battleships were being built). Experimental VH plates were made by the Japanese during WWII and some of these and many production MNC, NVNC, CNC, and VH plates (see above) were brought to the U.S. Naval Proving Ground, Dahlgren, Virginia, after the war for testing. Most of these plates, including the thick, production VH plates, showed that they were not much better than their WWI counterparts (which is not really bad for VH considering this was the best showing of any non-cemented armor actually used aboard ship and that the Japanese were not trying to make a better armor, just make British WWI-quality armor cheaper). An experimental 7.21" (18.15cm) VH plate seems to have been made from a German KC n/A (see above) specification added to an otherwise standard VH plate. It had a 535 Brinell maximum face hardness 3% into the plate, which is the hardest of any VH plate that I know of, though only by a small amount, with the hard point the closest to the face surface (about the same distance from the face surface (0.22" (0.55cm)) as with most cemented non-German KC-type plates), and a back hardness of 210-215 Brinell, which is slightly higher than production VH, but still well below average WWII-era KC-type plates. The steel used was identical to the production VH plates that had been tested previously and the hardness curve showed a typical VH-style pattern for the high-hardness portion. However, the major difference between this plate and all other VH plates was that the transition layer was much wider, extending to 43% into the plate (57% unhardened back), almost identical to German KC n/A, though with a higher average hardness than KC n/A in the decrementally hardened region. Since Germany and Japan were allies during WWII, it is not surprising that the Japanese may have obtained such information on German Krupp armor and made test plates to compare it with their own armor. The U.S. test personnel at the U.S. N.P.G. did not expect it to be much different from the production VH plates, especially due to its relatively poor steel quality. However, this plate was found to be the best face-hardened plate of its thickness ever tested at the U.S. N.P.G.! (The next best plate of similar thickness was also an experimental non-cemented face-hardened plate of 7.6" (19.3cm) thickness made by Carnegie-Illinois Steel Corporation during WWII, which was only slightly inferior to this VH plate.) It required the late-WWII, improved, super-hard-capped (650-680 Brinell all the way through) U.S. 8" (20.3cm) Mark 21 Mod 5 AP projectiles to completely penetrate this plate in "effective" condition at 30^o obliquity (the standard U.S. armor test in WWII)--the older Mod 3 projectiles, similar but with a maximum cap hardness of 555-580 Brinell, were torn up badly even when they completely penetrated (a rare feat against these U.S. projectiles!) and needed a much higher striking velocity to do so. Against the Mod 5 projectile, my calculations indicate that this plate was 1% better on an equivalent thickness basis than an average KC n/A plate (probably because the VH plate does not lose any resistance due to the existance of the thin, but very brittle, cemented layer used in KC n/A armor), meaning that it would take an average 7.28" KC n/A plate to replace this 7.21" VH plate--a pretty big improvement from regular VH armor in a single step! The U.S. test personnel were at a loss to explain this, but to me it seems that the Japanese personnel used the face tempering process of KC n/A, possibly with some of their own expertise added, in addition to just increasing the chill thickness. Japanese metallurgists (and most other technical personnel) obviously were (and are still) just as good as anybody else when allowed to set their own standards of excellence, as the post-WWII world has discovered big-time! NOTE: The 26" VH turret face plates on the YAMATO Class were inclined back 45^o and were the only plates that could not be completely penetrated by any gun ever put on a warship--these plates could be holed at point blank range by a newly-lined WWII U.S. Navy 16"/50 gun with late-WWII hard-capped AP projectiles, but even these projectiles would always ricochet; the YAMATO's own 18.1" (46cm) hard-capped AP projectiles, which were designed to an only slightly-improved British circa-1921 armor penetration specification, could not even make a hole in these plates at any range, though the impacts might crack them!
ARMOR QUALITY: Q=0.839 and QD=Q BLT: 65 TC=N CW=N SS=N

AVE. WWI-ERA CLASS "A" ARMOR
USAGE: Vertical armor 4" (10.2cm) and thicker.

Average value of the armors made by the three major U.S. naval armor manufacturers of the time--Carnegie Steel Corporation (the largest), Bethlehem Steel Corporation, and the Midvale Company (the smallest)--based primarily on Carnegie Krupp Cemented (CKC), a slightly modified version of original Krupp Cemented armor, which was similar to the average KC-type armors made by the other two during this period. However, in an attempt to get more of this market, the two smaller armor manufacturers developed several radically different forms of face-hardened Chromium-Nickel-steel armor. Bethlehem introduced in several ships from 1906-1910 a form of face-hardened armor that relied completely on its deep face without the cemented layer (Bethlehem Non-Cemented Class "A" armor), which had a very large percentage of Chromium (3.5%), the largest amount of Chromium ever used, to my knowledge, and Carbon ( 0.45%) and a rather low percentage of Nickel (2.25%). It was used as part of the armor (mixed with Midvale and Carnegie plates in a crazy-quilt pattern) in the battleships USS SOUTH CAROLINA, DELAWARE, NORTH DAKOTA, FLORIDA, UTAH, ARKANSAS, and WYOMING. It was very brittle and many plates cracked after installation, as well as having severe face spalls (deep flaking of the surface on impact) during acceptance testing, so it was discontinued in 1910 and a CKC-like armor was re-introduced. Later testing of 12-13.5" (30.5-34.3cm) plates of this armor in 1920-21 using the new, improved 12" "Midvale Unbreakable" or "Midvale 1916" soft-capped armor-piercing projectiles showed that this armor barely met minimum specifications and had no redeeming characteristics, being noticeably inferior to average CKC plates. During this same time frame, Midvale also came out with its own MIDVALE NON-CEMENTED CLASS "A" armor (MNC) (see below) which had some rather unusual properties. It too was brittle (though not nearly as bad as the Bethlehem Non-Cemented armor) and it too was discontinued in 1912, after which Midvale also reverted to a CKC-like Class "A" armor. In 1921, some problems with its armor plant, the invulnerability of the new Midvale projectiles to the CKC-type armors then in use, and the good showing of the experimental Carnegie 13" (33cm) STS plates (see above) made Bethlehem develop a unique form of cemented face-hardened armor with only a 15% face and transition layer combined, similar to a Harveyized plate, called BETHLEHEM THIN CHILL CLASS "A" armor (BTC), also with unusual properties (see below), that was used in some of the last U.S. battleships and in the ships canceled by the Washington Naval Treaty of 1922. It was also made by Midvale under license in 1922 and 1923. Carnegie kept making its gradually improving version of CKC.
Up through the end of 1910: .ARMOR QUALITY: Q=0.828 and QD=Q BLT: 65 TC=N CW=Y SS=N
1911-1923:. . . . . . . . . . . . . . .ARMOR QUALITY: Q=0.889 and QD=Q BLT: 65 TC=N CW=N SS=N

MIDVALE NON-CEMENTED (MNC) CLASS "A" ARMOR
USAGE: Vertical armor 4" (10.2cm) and thicker.

Used as portions of the Class "A" armor of battleships USS NORTH DAKOTA, FLORIDA, UTAH, WYOMING, ARKANSAS, NEW YORK, TEXAS, and OKLAHOMA, especially 12-13.5" (30.5-34.3cm) belt armor. Extremely constant face hardness to 25% plate depth and then a very gradual "ski-slope" hardness drop-off to the 200 Brinell level at only 18% of the plate's thickness from the back (the deepest face plus transition layer combination of any plate type that I know of). The plate used a high 0.55% Carbon to ease the hardening process somewhat, but was otherwise of more-or-less standard KC composition. The high Carbon content and the very thick hard face made these plates somewhat brittle, as noted above, but not extremely so. At the time that this armor was manufactured, it, along with rival Bethlehem Non-Cemented armor (see above), was not considered unusual in any way ballistically. When some of this kind of armor was re-tested in 1921 using the new 12" (30.5cm) "Midvale Unbreakable" or "Midvale 1916" projectiles, which had remained unbroken in 90% of their tests at right-angles against any other kind and thickness of face-hardened armor (including WWI British KC and German KC a/A (see above)), the projectiles completely shattered, acting as if their armor-piercing caps were not there at all! Midvale made some more plates using their old MNC recipe, but adding a cemented face layer, and got the same result, though it was found that only a specific range of heat treatment temperatures worked (this was later understood as "temper brittleness" in the 1930's when metallurgical expertise had improved). This unusual result caused Midvale to make a single lot of cemented MNC-type plates for one of the canceled warships. However, re-testing of these plates using the newer 14" (35.56cm) and 16" (40.64cm) sizes of the Midvale Unbreakable projectiles showed that the projectiles still shattered, but the improvement in resistance dropped very steeply with increasing projectile size; a huge "scaling" effect that completely nullified any ballistic improvements when the 14" projectile size was used and actually resulted in the armor being no better than HARVEYIZED NICKEL-STEEL armor (see above) against unshattered (!!) soft-capped projectiles when the 16" projectile size was used (even with shatter occurring!). The super-thick face, which failed by fracture along surfaces, not by deformation and tearing through a volume as did ductile material, was the culprit. Needless to say, with 16" guns being used on all new U.S. battleships, Midvale had to abandon its MNC-type armor for a second time and started making BETHLEHEM THIN CHILL armor (see below) under license until all heavy armor manufacture stopped in 1923. WWII testing with the very good hard-capped U.S. 14" Mark 16 Mod 8 armor-piercing projectile type showed MNC armor to be unable to shatter these projectiles and to be very poor ballistically, in line with the poor showing of the large-caliber projectile tests of 1921. Unfortunately, the effectiveness of the very thick face of MNC armor encouraged all U.S. manufacturers to try to use a thick face (but retaining a thick back by narrowing the transition layer) against their improved post-WWI APC projectiles, which eventually proved futile, but which had the side-effect of increasing the scaling factor so that the heavier grades of WWII U.S. Class "A" armor were inferior to thinner-faced British, German, and, I assume, French face-hardened armors, though the armor was otherwise equal to them in all respects (see below).
ARMOR QUALITY: Q=0.881 and QD=Q BLT: 18 TC=N CW=Y SS=Y

BETHLEHEM THIN CHILL (BTC) CLASS "A" ARMOR
USAGE: Vertical armor on USS WEST VIRGINIA Class (and canceled post-WWI battle-cruisers and battleships) over 4" (10.2cm).

Developed in 1921 after some problems with the manufacture of standard CKC-type Class "A" armor (see above) halted production. During this time the very good showing of the Carnegie 13" (33cm) STS plates (see above) occurred and it also became evident that the new "Midvale Unbreakable" or "Midvale 1916" armor-piercing projectiles were practically invulnerable to damage at up to 15^o obliquity (the maximum obliquity test standard during this period was circa 10^o for caliber-thickness armor from any nation) from any form of then-current face-hardened armor (the unusual results of the testing of MIDVALE NON-CEMENTED CLASS "A" armor (MNC) (see above) were not yet known). It was decided by Bethlehem Steel Corporation that a better form of Class "A" armor should be developed reflecting these facts, rather than just continuing with the current very standard slightly-modified-original-KC-type armor (see KC a/A, above) being manufactured in the U.S. and abroad. Since the face was not working very well against the Midvale projectiles, yet at oblique impact even HARVEYIZED NICKEL-STEEL armor (see above) would shatter them (it was not yet known that only soft armor-piercing caps were limited to 15-20^o obliquity and that replacing them with hard--well over 300 Brinell at their forward surface--caps and then carefully controlling the projectile's hardness pattern could greatly expand the oblique impact ability of projectiles against even the heaviest face-hardened armor), and since Class "B"/STS armors (see above) of similar thickness were equal to or better than Class "A" armor at low obliquity (under 20^o when there was no shatter) and at high obliquity (over 55^o obliquity, especially when shatter occurred, which inhibited ricochet), the designers at Bethlehem simply made a normal cemented face-hardened Class "A" plate with the depth of hardened face behind the cemented surface layer reduced to only about twice as thick as the cemented layer (circa 15% of the entire plate's thickness for most plates in the 9-16" (22.86-40.64cm) range made at the time). The face was not eliminated completely since it was better than a non-face-hardened plate in the critical 20-55^o obliquity region where most impacts would occur at long range due to the angle of fall if nothing else (the U.S. Navy was already specifying long-range fire supported by aircraft spotting as the "wave of the future" in naval gunnery) and since it was better against smaller uncapped projectiles under almost any conditions. When the (short-lived) good results of the very-thick-faced MNC armor occurred and the Midvale Company made a new batch of that armor with a cemented surface, the U.S. Navy had the unusual "honor" of having both the thickest-faced and thinnest-faced forms of KC-type armor ever made, as well as a more-or-less normal KC-type armor in Carnegie's CKC, being produced for its ships at the same time! When the new MNC armor type was found to have a huge scaling effect that degraded it against larger projectiles, Midvale gave up on it and began making BTC under license. The cancellation of all of those post-WWI battleships and battle-cruisers resulted in a very large amount of excess armor of all kinds being stored at the U.S. Naval Proving Ground in Dahlgren, Virginia, and other places. Some of it was used as experimental plates comparing improved projectiles between WWI and WWII and it was found that BTC armor made by either Bethlehem or Midvale could not damage the new hard-capped armor-piercing projectiles introduced by the U.S. during the 1920's, 1930's, and 1940's until the impact obliquity was increased to at least 40^o, an obliquity well above the ability of any foreign projectiles to handle, as was determined by post-WWII testing of British, Japanese, and German projectiles of various types. However, since there were so many plates available, acceptance testing of large-caliber armor-piercing projectiles was performed using BTC plates at 40^o obliquity during most of WWII, after an experimental period calibrating the damage these plates gave compared to similar plates of modern post-1930 U.S. Navy Class "A" armor, which had a very thick face (see below), at the usual 30^o obliquity (sometimes 35^o). The experience with BTC armor and MNC armor indicates to me that for significant projectile damage, a face of substantial thickness was needed, but this thickness of face must be kept at the minimum possible for thick plates to prevent excessive scaling effects, though for thin face-hardened plates--under circa 7" (17.78cm) thick--a thicker face (within reason) actually increased resistance as the scaling factor worked in reverse to benefit thin armor. Also, as U.S. MNC and Japanese VH face-hardened armors (see above) showed, the cemented surface layer was useless against high-quality, hard-capped WWII APC projectiles and should have been eliminated (saving both time and money).
ARMOR QUALITY: Q=0.889 and QD=Q BLT: 85 (average) TC=Y CW=N SS=N

AVE. WWII-ERA CLASS "A" ARMOR
USAGE: Vertical armor from 5" (12.7cm) up except for 16" (40.64cm) & up turret face (port) plates.

When U.S. naval armor again began to be developed and manufactured for new ships and for rebuilding older battleships, the lack of ability of BTC (see above) to cause enough damage tothe improved U.S. hard-capped armor-piercing projectiles being developed and introduced continuously was well known, so the trend was to increase the face depth to increase the damage-causing ability of the Class "A" armor, which was already undergoing a major improvement by the increase in toughness due to better metallurgical skill in general (the new plates could shatter the now-obsolete "Midvale Unbreakable" or "Midvale 1916" projectiles (see MIDVALE NON-CEMENTED armor, above) even at right-angles, which only Midvale's unusual pre-WWI MNC armor was known to be able to do before)--German KC n/A (see above) also had a somewhat thickened face for similar reasons, though to a much lesser degree. Unfortunately, U.S. armor-piercing projectiles just kept getting better and better, so the face thickness just kept getting thicker and thicker, until a average of about 55% of the plate was face and transition layers (35-40% face and 15-20% transition layer). Even with this level of face thickness, which was the heaviest face ever used except by MNC armor, the better U.S. armor-piercing projectiles eventually became so unbreakable that the test specifications near the end of WWII said in some cases that, if the projectile could not be damaged by the armor, do not worry about it and go on to other kinds of tests! I know of at least one test where a U.S. 14" (35.56cm) Mark 16 Mod 8 hard-capped armor-piercing projectile (introduced in 1943 by the Crucible Steel Company, the largest and best U.S. naval projectile manufacturer for many years, and probably the best all-round naval armor-piercing projectile used during WWII) completely penetrated in effective bursting condition (no significant lower or middle body or fuze damage) a 13.5" (34.29cm) brand-new Class "A" armor plate at 49^o obliquity at just above the Navy Ballistic Limit velocity, where the projectile just barely makes it through the plate and where maximum damage usually occurs to a completely penetrating projectile. (Such a result would be almost impossible to even imagine with any foreign projectile design!) The thick face added to the scaling effect, though not nearly as much as the face of MNC had, making thick U.S. WWII Class "A" armor somewhat inferior to German KC n/A or British CA (see above), but also working in reverse so that U.S. WWII Class "A" armor 7" (17.78cm) or less in thickness was the best face-hardened armor used by anyone ever. The replacement of Class "A" armor by Class "B" armor in the heaviest grades that were used in WWII battleship turret face plates demonstrates that the U.S. Navy was aware of the relative inferiority of its thick-faced Class "A" armor in such heavy grades against high-quality projectiles. The steel quality of this armor was equal to the best foreign armor and quality control was rather good, though Midvale armor tended to crack more than the other two manufacturers' Class "A" plates (Carnegie-Illinois Steel (later U.S. Steel) Corporation and Bethlehem Steel Corporation).
ARMOR QUALITY: Q=1.00 and QD=Q BLT: 45 TC=N CW=N SS=Y

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. . . . My knowledge of French naval armor is very limited, but I know that it introduced many of the basic metallurgical improvements used by armor and construction steel during the 19th and early 20th Centuries. The following are some information that I know of concerning French naval armor in the 20th Century:

. . . . 1) France introduced Molybdenum in 1912 to improve the manufacturing process for naval armor by increasing the hardenability and toughness of the steel and by making the metal tougher when in its high-temperature solid austenite form. This indicates to me that French WWI-era armor was the equal to the best foreign armor, at least in standard manufacturing processes, steel quality, and so forth.

. . . . 2) French naval designers decided during the 1930's that steeply-falling armor-piercing aircraft bombs would be more of a threat than more shallow impacts by medium-to-long-range naval gun projectiles and they therefore had face-hardened armor used for all plates over 4" (10.2cm) on turret and conning tower roofs where layered protection (spaced decks) was not possible. To my knowledge, no other nation did this. Ironically, while this idea turned out to be absolutely true in almost every case in WWII, the one case where a French main turret roof--a 5.91" (15cm) roof plate on the battle-cruiser DUNKERQUE--was hit was not by an aircraft bomb, but by a 15" (38.1cm) 1938-pound hard-capped armor-piercing projectile at about 70-75^o obliquity fired by the HMS HOOD at close range. The projectile broke in half and the nose ricochetted off, but the projectile lower body did not ricochet and the plate ended up with a large, projectile-shaped hole in it (it actually seems to be an outline of the British projectile on its side pushed into the plate!), throwing a large amount of plate material into the turret at high velocity, followed by the lower portion of the projectile, which then exploded (probably a less-than-full-strength explosion, but what difference did it make?) inside the turret, knocking out the right half of the split 4-gun mount (each turret was divided by heavy internal armored bulkheads into two adjacent 2-gun turrets on one mount, a unique French design). If the armor had been homogeneous, the projectile would have ricochetted off in one piece and probably no armor would have been ejectedfrom the plate hit.

. . . . 3) French WWII-era armor test results (I have a couple) give their face-hardened armor a perfect fit (my formulae give the exact (!!) complete penetration velocities found inthe tests) for an armor of the best WWII-era plate quality using the 35% face of original German KC armor (i.e., Krupp WWII KC n/A with a Krupp WWI-era KC a/A face depth).

. . . . 4) In 1938-39 an experimental 5.91" (15cm) KC-type plate was manufactured that was standard except that it had been "baked" in the cementing oven for an entire year (!!). After the fall of France in 1940, the Germans took this plate back to Krupp where it was found to give unusual (I bet!) ballistic performance. Does anyone know more about this plate?