Footnotes for Best Battleship Page: Armor

Calculating any sort of a 'ranking for armor protection was very, very difficult. Here's what I did:

Step one: Underlying Approach

I am going to create an Overall Rating based on two sub-ratings, one for the ships' belt protection, the other for their deck protection. In my mind, deck protection was slightly more important in WWII than belt protection, for two reasons. One; the advent of radar fire-control made the longer-range engagements possible, and heightened the importance of deck protection. Two: aircraft attack profiles become of increasing concern to capital vessels, and aircraft tend to attack deck armor [Remember: anti-torpedo defenses are treated in another section]. Consequently, I will weight Deck protection vs. Belt protection at 60/40.

Step Two: Belt Armor Index

Using Nathan Okun's article on battleship protective schemes, I quantified their total vulnerability zone range (using the Navy Ballistic Limit as the benchmark for penetration). For instance, Bismarck could put a shell through her own belt from any range under 29,000 yards (the weakest score), whereas she would have to close to within 16,400 yards to punch through Iowa's (which had the best). [Note: for the purposes of this computation, I am rating Iowa's side protection as equivalent to South Dakota's, which is the ship Nathan actually shoots at in his article. Iowa's belt scheme was practically identical to South Dakota's, and both had STS shell plates outboard which serve to de-cap incoming AP projectiles, which is why (stunningly) South Dakota's belt is slightly more effective than Yamato's!] Here are the ratings:

Raw Armor Rating Yamato Iowa Bismarck Richelieu King George V Vittorio Veneto South Dakota
Vulnerability zone ('000's of yards) 17.7 16.4 29 20.8 21.5 17.5 16.4

Remember, in the above table, smaller means better, because the opposing ship has to get closer to you to get through your belt. Next, I arbitrarily said, OK, Iowa has the best rating, so she gets a '10', and Bismarck has the worst (by a ton), so she gets, ummmm, a '5'. Why a '5'? Well, why not? Plus, I was scandalized by the width of her vulnerability zone. I mean, 29,000 yards is just really lame! So that's what I decided. And I spaced out the other four ships accordingly. Here are the belt ratings that resulted:

Step Two Yamato Iowa Bismarck Richelieu King George V Vittorio Veneto South Dakota
Rating 9.5 10 5 8.5 8 9.5 10

Step Three: Deck Vulnerability Rating

This was really, really complex. Again, I used Nathan's article to calculate the total width of the deck vulnerability zones, in thousands of yards, considering Bismarck's maximum range of 39,000 yards. There was an obstacle to overcome here, though. Nathan has calculated vulnerablity zones for every possbile broadside trajectory against these ships using the German 15" gun. However, some areas of the armor deck are more likely to be hit on a given ship than others. Nathan has broken these target areas down into 'Large', 'Small', and 'Tiny'. That's great, but how big is 'Tiny'? I arbitrarily said, Large = 75%, Small= 20%, and Tiny = 5%, and weighted the trajectories accordingly. As an example, here are King George V's vulnerable deck zones versus Bismarck's 15" gun:

Step Three: Part One Trajectory in Question Vulnerability Zone Width Deck Target Size Base % to hit Weighted % to hit Weighted width of vulnerability zone
Through .45-1" weather deck and 5.17" armor deck 39,000 minus 33,200 = 5,800 yards vulnerable zone 'Large' 75% 39% .395 times 5,800 = 2,289 yards
Through .675-.9" upper side hull and 5.17" armor deck 39,000 minus 33,200 = 5,800 yards vulnerable zone 'Small' 20% 10.5% .105 times 5,800 = 610 yards
Through .45-1" weather deck and 6.15" armor deck (over magazines) 39,000 minus 36,600 = 2,400 yards vulnerable zone 'Large' 75% 39% .395 times 2,400 = 947 yards
Through .675-.9" upper side hull and 6.15" armor deck (over magazines) 39,000 minus 36,600 = 2,400 yards vulnerable zone 'Small' 20% 10.5% .105 times 5,800 = 252 yards

Okay, let's walk through this. Basically, ya got two 'Large' targets and two 'Small' targets to shoot at on King George V's deck, so the hit distribution will be as follows: 39.5% + 39.5% + 10.5% + 10.5% = 100%. But the first 'Large' target is much more vulnerable than the second. So multiply the weighted hit % times the width of each vulnerability zone (i.e. 39.5% times 5000 yards = 2,289 yards) to arrive at a weighted width of each vulnerability zone. Then, for the final step, total up the yards for all the vulnerability zones. In King George V's case, the total weighted vulnerability zone is roughly 4,100 yards (2,289 + 610 + 947 + 252 = 4,098 yards).

Good. Now do this for all seven ships. I'm not going to put this up in HTML because it's just too much of a pain. If you want the spreadsheet I used to figure this all out, I'll be happy to send it to you. The final vulnerability zone widths look like this:

Step Three: Part Two Yamato Iowa Bismarck Richelieu King George V Vittorio Veneto South Dakota
Weighted Vulnerability Zone (000's of yards) .04
Yes, that's right: a weighted deck vulnerability of only 40 yards!		 2.93 7.01 .92 4.10 14.65 2.93

So now it's time to apply some ratings to all this. Again, I arbitrarily assigned a rating of between '5' and '10'. Yamato's deck is awesome (and gets a '10'), and Vittorio Veneto's is pathetic (and gets the '5'), so there you go. Everyone is somewhere in between.

Step Three: Part Three Yamato Iowa Bismarck Richelieu King George V Vittorio Veneto South Dakota
Deck Rating 10 9 7.5 9.5 8.5 5 9

Step Four: Composite Armor Rating

Okay, now we take the two ratings and weight them 60% vs. 40% Deck/Belt. And you end up with:

Step Four Yamato Iowa Bismarck Richelieu King George V Vittorio Veneto South Dakota
Belt Rating 9.5 10 5 8.5 8 9.5 10
Deck Rating 10 9 7.5 9.5 8.5 5 9
Weighted Armor Rating 10 9.5 6.5 9 8.5 7 9.5

Step Five: Final Armor Rating

Finally, the part I love: dinging ships for their flaws. Bismarck gets a half point ding for leaving some very important hydraulics above the level of the main armor deck. King George V and Vittorio Veneto both get dinged for having inadequately armored control positions topsides.

Step Five Yamato Iowa Bismarck Richelieu King George V Vittorio Veneto South Dakota
Overall Rating 10 9.5 6 9 8 6.5 9.5