Yokosuka D4Y

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Image:D4Y Yoshinori Yamaguchi col.jpg Image:D4Y3 pulling up.jpg Image:Yokosuka D4Y3 in the field.jpg The Yokosuka D4Y Suisei (彗星, "comet") was a dive bomber of the Imperial Japanese Navy. Its Allied codename was "Judy".

It was developed starting in 1938 at the Yokosuka Naval Air Technical Arsenal, based on two Heinkel He 118 dive bombers that had been supplied by Germany. The first D4Y1 prototype made its maiden flight in December 1940, and proved to possess an excellent combination of high performance and good handling. After the prototype's successful trials development was sped up, the first unpleasant surprise came. Although well-proportioned and purposeful in appearance, service trials demonstrated weakness in the wing structure. During dive-bombing trials the wings of the D4Y started to flutter, so much that it could break up the wing spars, a fatal flaw for an airframe subject to the stresses of the dive bombing manoeuver, and the initial models were used as reconnaissance planes starting in late 1942. Two early aircraft joined the fleet in time for the battle of Midway, when one was used in action.

The structural problems were fixed by March 1943, and ultimately 2,038 were produced, mostly by Aichi.

In the early versions the Yokosuka D4Y Suisei was hard to keep serviceable since the liquid-cooled Atsuta in-line inverted-V12 engines were unreliable and difficult to maintain. Already since the beginning there were voices heard that argued the Suisei should be powered by an air-cooled radial, the type of engine Japan had experience with and trusted.

As soon as time permitted the Aichi design team therefore looked for a radial engine, and the Mitsubishi MK8P Kinsei 62 radial, rated at 1,560 hp (1.163 kW), was selected, which resulted in the Yokosuka D4Y3 Model 33 with 14-cylinder two-row radial engine. The drawback of the radial engine version was the fact that the forward and downward view of the pilot worsened, hampering carrier operations.

The D4Y series of dive bombers were very fast for this type of aircraft and some were even converted to night fighters against the high flying B-29 bombers later in the war. At the 11-th Naval Aviation Arsenal at Hiro the Japanese attempted to make a D4Y2-S night fighter: all bomb equipment was removed and a 20-mm Type 99 Model 2 cannon with its barrel slanting upwards was installed in the place of the gunner's cockpit - but the lack of radar and slow climb rate made the Suisei night fighter ineffective.

Lacking armor and self-sealing fuel tanks, the Suiseis did not do well against Allied fighter aircraft. They did, however, cause considerable damage to ships, including the carrier USS Franklin, which was nearly sunk by a single "Judy".

The D4Y was operated from the following Japanese aircraft carriers: Chitose, Chiyoda, Hiyō, Junyō, Shinyo, Shōkaku, Sōryū, Taihō, Unryū, Unyo and Zuikaku.

The last version in the production was the D4Y4 Special Strike Bomber Model 43. This one-seat kamikaze airplane (scale model) capable of carrying one 800-kg bomb was launched into production in February 1945. It was equipped with 3 RATO boosters for taking off from short runways and with terminal dive acceleration.