Preface: Every nation during WW II “over-reported” its success on the field of battle. It’s just human nature, I suppose, but wishful thinking or overconfidence exaggerated individual performances when the mission’s success was reported to superiors. In most nations’ armed forces, the claimed success was evaluated by trained intelligence specialists, and careful piecing-together of the day’s events usually led to a considerably toned-down version that discounted much of what was reported. Sometimes that was resented by the participants, but usually the claims exceeded the actual results by a couple-hundred percent. Even conservative estimates by intelligence usually were overly-optimistic.
For some reason, the Japanese were the “worst” of the major nations in correctly evaluating battlefield success, and wild claims were believed by evaluators. These false successes laid the basis for operational shortcomings at the highest levels that hampered future operations through overconfidence and gross underestimation of the enemy’s real strength. Rampant imaginations of returning fliers reported fleets of enemy carriers and battleships burning and sinking, when in actual fact none were sunk and few were even hit. Surely in the long-range, overwater battles of the vast Pacific, verification of success would be difficult. Herewith I present a partial solution to help close the “gap” between imagined and real success.
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In 1940 two illustrious personages of the Imperial Japanese Navy collaborated on a paper submitted to the Naval War College Board on the importance of evaluating battle success. Rear Admiral Tamon Yamaguchi, Chief of Staff to the Japanese 5th Fleet from 1938 to 1940, and Vice Admiral Chuichi Nagumo, commandant of the Naval War College, had different temperaments, but were dedicated to the proposition that Japan must prevail in any war with the Western Powers. The paper emphasized scouting, reconnaissance, communications, and accurate battle results-assessment as vital force-multipliers in carrier battles. In essence, they proposed that a fast-flying aircraft with great endurance be created as a “strategic reconnaissance” scout that would enable an on-station report of the battle’s progress without having to rely on individual bomber pilots’ over-optimistic evaluations. Emphasis was placed on good (radio) communications while on station, and prodigious photography for analysis when the plane got back to the carrier. A few such aircraft could maintain a near-constant presence.
The current thinking on reconnaissance was to use cruiser floatplanes or large, multi-engined flying boats. These were economical, and freed up the carriers for purely strike aircraft but they were slow and could not land aboard the fleet carriers. Because they were so slow, they also had to hide in clouds and use other ruses to escape discovery and interception, and thus lost contact with the fleet they were spying upon.
The proposed aircraft would have an especially powerful engine for fighter-like speed, tremendous endurance via fuel capacity (disposable drop tanks, too), modern radio and direction-finding gear, and high-resolution still and video cameras. Presumably, three such aircraft would be kept aboard the flagship aircraft carrier of a division and rotated out to sea during a battle—one on station, one being readied, and one in the air or ready to launch to maintain continuous surveillance of the battlefield. Future fleet carriers should have an athwartship catapult on the hangar deck, as was the custom aboard US fleet carriers, to leave the flight deck free. Consequently, in 1940 the Imperial Japanese Navy wrote up the “C6” specification for a single-engined, carrier-based reconnaissance plane with a top speed of no less than 350 knots (403mph) at 6,000 m., and range of 2,500 nautical miles (4,960 km).
Yokosuka/Aichi had designed a strategic reconnaissance prototype that had “fighter speed” and high fuel capacity. The prototype was deliberately given room for additional fuel cells, both as drop tanks attached to the wings, and a jettison-able “belly” tank semi-recessed in the ventral fuselage. A newly-proposed Atsuta 22 v-12 engine, based on the Daimler-Benz DB 605N with GM-1 nitrous oxide boost would give 1600 horsepower. To take advantage of this prodigious power, they chose a four-bladed propeller (first to be found on Japanese planes). The engines for the initial batch of aircraft had come from directly from Germany via the auxiliary cruiser “Thor” and been tinkered with by Heinkel engineers to produce higher-than-normal output much like their racing engines. They required C3 100-octane aviation fuel, a rarity in Japan, that would have to be kept in special drums aboard the carriers (not endearing itself to fuel handlers, who had to pump it manually, and presenting an acute fire hazard in the hangar deck). Top speed was just over 400 mph loaded with minimum fuel, and only slightly less speedy fully loaded. The plane could certainly outrun any fighter currently in Japanese or German inventory. The rival, three-place Nakajima C6N Saiun couldn’t quite meet the speed specifications, so the Yamagumo was chosen.
The pilot/observer would be a busy man on the scene of battle, but had help. Human accomplices, as in the Nakajima aircraft, added too much weight that could be better used for equipment or fuel. Radio direction-finding gear and communication radios filled the space immediately behind the pilot. Cameras could be mounted pointed downward through Perspex panels in the lower fuselage, either still and/or video. A cockpit periscope allowed the pilot to see what was being filmed. Fearing that petroleum smears from the engine or fuel tank could smudge the Perspex, a boundary-layer deflector just forward of the lenses directed air around the cameras and back out behind to keep them clean. A dorsal air scoop and ducts fed clean air in behind the deflector to preserve airflow and keep out eddies. The Perspex was covered by the Japanese version of “Saran Wrap” and removed seconds before launch to maximize clarity. They figured any leakage greater than what the duct could handle would probably endanger the aircraft anyway. Extraordinary measures (for the time) were taken to preserve the aircraft and pilot in order to help insure that the valuable information returned to battle commanders. Self-sealing fuel tanks, pilot seat armor, radio and homing devices, and a parachute were “standard issue”. The pilot/observer was usually a captain, or at least an experienced lieutenant, selected from intelligence officers and taught to fly, rather than a flier taught ship recognition and signals.
The plane was named Yamagumo (“Mountain Clouds”) in keeping with the “cloud” images for reconnaissance aircraft. It was no random coincidence that the name incorporated parts of the names of its conceivers. At the insistence of the IJN, a single light machine gun was put in the forward fuselage in case the Yamagumo had to defend itself, or found a too-juicy target that could be safely engaged. Four fake, painted-on “gun ports” were put in the wings for whatever intimidation factor that could muster. The only known Yamagumo kill of the war was over China when, in a diving pass from above, a lone I-153 on a training flight was shot down.
A shortage of 100-octane fuel as a result of the Allied embargo resulted in an incident kept secret at the time. A neutral Soviet Vladivostok-bound tanker from the US carrying 100-octane fuel was stopped and confiscated by the Japanese. The fuel was pumped out, the ship scuttled after a phony distress message, and the sailors interred. The Soviets were led to believe the ship sunk by hitting a mine. Japan paid the Soviets some compensation, but at least they had their fuel.
Aboard the super-carrier Yonaga (7th Carrier Division—Vice-admiral Nagumo) and Soryu (2nd Carrier Division--Rear Admiral Yamaguchi) on December 7th, 1941, two Yamagumos with the “German” batch of engines took off to scout Pearl Harbor and Lahaina Roads, respectively, for American fleet units, and to see if there was any sign of alertness to the oncoming raids. In the style of “Suterusu”, or “stealth”, their bright red Hinomarus and other colors were lightly overpainted with a mist of standard gray paint to obscure, but not eliminate, the obvious Japanese markings. The normally bare-metal fronts of the propeller blades were also painted so a glint didn’t give them away. Surprise was achieved in the early morning light, and there was no sign the planes were detected. The Yonaga’s Yamagumo over Pearl Harbor reported back that land planes were lined up in rows, canvas shrouds covered AA guns aboard ships in the harbor, and they detected no standing fighter patrols. Initial verbal reports over the radio indicated, disappointedly, that no American aircraft carriers were in harbor.
When the Yonaga’s first Yamagumo was relieved by another, it returned to the carrier and the cameras were immediately removed and the film rapidly processed. As evaluators poured over the photographs, it seemed that a large carrier was anchored near a light cruiser at the west end of Ford Island (the ship optimistically identified as a carrier was actually the old target ship Utah.) Unbeknownst to the photo interpreters, a tiny screw lying on the hangar deck before launch was kicked up by the propeller blast into the Perspex over the lenses and nicked the plastic, creating the illusion of a “deck” on the ensuing photograph. The attack bombers launched earlier and about to enter Hawaiian airspace were alerted, and indeed attacked this “carrier”. Only after a similar mark appeared in the same spot in other photos was the error revealed, but the attack on the “carrier” was already under way.
The US Fleet carriers discovered off Hawaii by the Soryu’s Yamagumo sent up their F4F’s on full blower to intercept, but the Yamagumo pilot radioed back, “No Grummans can catch us!” The Soryu Yamagumos orbited the American carriers at high speed and guided the next wave of Japanese bombers toward them instead of Pearl Harbor. But the Yonaga’s C6Y was tracked by USS Enterprise’s radar (they were amazed at how fast the blip was moving) when it flew back to its carrier and an attack was sent out to the source.
The loss of the super-carrier Yonaga off Hawaii during the Pearl Harbor raid was attributed to uncontrollable fires from an American bomb exploding amongst the stored drums of 100-octane fuel. This led to a ban on the Yamagumo’s use aboard carriers until a de-tuned, similar engine using “normal” 87 octane fuel from the protected tanks below decks could supplant the “racing” engines. The safer handling of fuel was deemed to make up for the loss of speed and transit time.
The concept was tested again when the British naval response to the Malaysian landings was detected by normal reconnaissance planes, and Yamagumos from the elite, land-based 22nd Air Flotilla hurried out to scout and report back as the lumbering torpedo bombers flew out to the scene. Like the scenario off Hawaii, HMS Insuperable’s “Waterspout” fighters could not catch up to the recce planes and soon had their hands full with the incoming bombers. This batch of aircraft, with the Japanese-built engine, suffered troubling engine failures and two Yamagumos were lost, though not through enemy action.
After much success with the C6Y1, and because the Yamagumo was thought to be nearly un-interceptable, fighter and bomber variants were proposed. What if it actually FOUND something in a vulnerable state (like a carrier with planes on deck)? It might be good to have an attack capability. The Americans were found to use their scout-bombers that way. The Air Technical Arsenal looked to see if small bombs could be carried, especially in the lower fuselage where the extra fuel was stored. They used the lower-performance Atsuta 32 engines not needing the 100-octane fuel, and substituted a three-bladed prop. Performance suffered dramatically, but this C6Y2 variant was still an improvement over the obsolescent Aichi D3A Type 99 “Val”. In mid-summer of 1942, a two-place dive bomber version was created and became the C6Y2-D Suisei (Allied code-name “Judy”), soon to become the more appropriate D4Y1. Both mass production and operational conversion from the D3A began, but the troubling engine failures were never fully rectified. Eventually, the Suisei’s were produced with proven radial engines, but no Yamagumos were fitted with radials.
For the strictly strategic scouting role once dominated by the Yamagumos, the rival C6N Saiun-Kai (Myrt), now with a laminar-flow wing, a more powerful and reliable radial engine, and a second observer, gradually supplanted the de-tuned C6Y2’s. To prevent smearing the camera lenses with engine effluent, the ventral oil cooler was rotated off the centerline rather than deal with the complex deflectors.
Because the Yamagumos were never intercepted, photographed, or identified, they were never given an Allied code-name. The few Yamagumos based in the Japanese Home Islands were used in late-war Kamikaze attacks, but went un-recognized and were reported simply as “Judys”.
About the model: A “standard” Fujimi D4Y Suisei was used, with dual cameras and Perspex from a DML Arado 234 kit, and a 4-blade propeller and boss from a Mustang. I kept the pilot's position but cut down the canopy to single-seat, filled in the GIB position from a Northrop N3B’s belly, scratch-built the deflector, and scratch-built a depression for the ventral fuel tank (spare from a Zero). Standard Hinomarus were used, with tail codes “G I- 801” meaning “[G] 7th Carrier Division, [I] First carrier in the Division (Yonaga—Owari was II), [8] reconnaissance aircraft, [01] plane number 1”.
