The Yokosuka D4Y Suisei was designed as a supplement for the Aichi D3A.
Yokosuka was the location for the Imperial Japanese Navy’s First Naval Air Technical Arsenal, which began to design a carrier-based single-engine dive-bomber in 1938. The resulting Suisei (comet), based on the Heinkel He 118, was unusual as it was one of few Japanese combat types to be powered by a liquid-cooled engine, in this case a licence—built copy of the German DB 601.
In service from autumn 1942, the type served initially in the reconnaissance role (D4Y1-C), with the dedicated dive-bomber version (D4Y1) entering service in 1943. The type did not fare well against high-performance Allied fighters, and many fell to their guns due to poor protection for the crew and the lack of self-sealing fuel tanks. A total of 2038 were built, the D4Y2 having a more powerful engine while the D4Y4 was a kamikaze suicide-bomber version which carried one 800kg/1761lb bomb. The Allied codename allocated to all versions was “Judy”.
- D4Y1 prototypes: five, powered by imported 960-hp (716-kW) DB 600G engines
- D4Y1 pre-production: generally as prototypes but with a 1,200-hp (895-kW) Aichi AE1A Atsuta 32 engine
- D4Y1-C: reconnaissance version of D4Y1 with camera in rear fuselage
- D4Y1 Suisei: initial dive-bomber production version; similar to prototypes but with strengthened structure and improved dive brakes
- D4Y1 KAI: as D4Y1 Suisei but equipped for catapult launching
- D4Y2: improved version introducing AE1 P Atsuta 32 engine; armament as prototypes
- D4Y2a: as D4Y2, but rear mounted 0.31-in (7.92-mm) machine-gun replaced by one of 0.51-in (13-mm) calibre
- D4Y2-C: reconnaissance version of D4Y2
- D4Y2a-C: reconnaissance version of D4Y2a
- D4Y2 KAI: D4Y2 with catapult launch points
- D4Y2a KAI: designation of D4Y2a with catapult launch points
- D4Y2-S: night~fighter conversion of D4Y2; bomb racks, rear ﬁring gun and carrier equipment removed; bomb bay sealed; single 20-mm cannon mounted obliquely in fuselage to ﬁre upwards and forwards, and some equipped also with air-to-air rockets
- D4Y3: generally as D4Y2 but powered by the 1,560-hp (1163-kW) Mitsubishi MK8P Kinsei radial engine
- D4Y3a: as above, but with armament of D4Y2a
- D4Y4: single-seat kamikaze attack version of D4Y3; standard forward-firing guns and one 1,764-lb (800-kg) bomb. 
- First ﬂight: November 1940
- Power: One Aichi 1400hp Atsuta 32 piston engine
- Axmament: Two 7.7mm/0.303in forward-firing and one 7.92mm/0.31 in rear-firing machine-gun; up to 800kg/1761lb bomb load
- Size: Wingspan; 11.5m/37ft 8.75in. Length; 10.22m/33ft 6.25in. Height; 3.74m/12ft 3.25in. Wing area ~ 23.6m2/254sq ft -
- Weights: Empty ~ 244Okg/537O|b. Maximum take-off; 4250kg/9354|i1
- Performance: Maximum speed; 550kph/342mph. Ceiling; 10,700m/35,105ft. Range; 1465km/910 miles. Climb; 820m/2700ft per minute.