Aichi Tokei Denki Kabushiki Kaisha, which was to become a significant aircraft design and construction company during World War II, had been established in Japan during 1899 as a manufacturer of electrical equipment and watches.
Aichi established a working relationship with Ernst Heinkel Flugzeugwerke in Germany and wishing to contend in early 1931 for an Imperial Japanese navy requirement for a two-seat carrier-based dive-bomber, requested Heinkel to design and build an aircraft to meet the navy's specification. Required for operation with float or wheel landing gear, the resulting Heinkel He 50 prototype flew in the summer of 1931 with twin floats. A second version, with wheel landing gear, was supplied to Aichi under the export designation He 66.
The He 66 was a two-bay biplane of metal construction with metal and fabric covering. The braced tail unit was conventional, and landing gear of fixed tailskid type. As supplied it was powered by a 365kW Siemens SAM-22B (Jupiter VI) radial engine. Modifications carried out by Aichi included strengthening of the landing gear, and installation of a 418kW/580-hp Nakajima Kotobuki 2 Kai 1 radial engine. In this form the Aichi Special Bomber was successful in trials against competing prototypes from Nakajima and Yokosuka, and was ordered into production as the Navy Type 94 Carrier Bomber (Aichi D1A1) in 1934. By 1937 162 production aircraft built, had the radial engine enclosed by a Townend ring, and other modifications included the introduction of slightly swept wings, and replacement of the tailskid by a non-castoring tailwheel. The last 44 had 433kW Kotobuki 3 engines.
Aichi's design team under Goake created an improved D1A2 with 730-hp Nakajima, Hikaru 1 engine in a full-length NACA cowl, spats and improved windshields. Production of this version totalled 428.
The first A2 flew late in 1936 and by 1940 Aichi had delivered no fewer than 428 as Type 96 carrier bombers. Most saw action in China, one unit dive-bombing and sinking the US gunboat Panay in the Yangtze in 1937.
Only a small number of D1A1s remained in use with training units at the time of Japan's attack on Pearl Harbor, on 7 December 1941. By December 1941 only 68 D1A2s were the serving in second-line units, and these were allocated the Allied codename 'Susie'.
Engine: Nakajima Kotobuki 2 Kai 19-cylinder radial 580-hp
Span: 11.4 m / 37 ft 4.75 in
Length: 9.3 m / 30 ft 6 in
Armament: two synchronized 7.7-mm (0.303-in) Type 92 machine-guns, one 7.7-mm (0.303-in) Type 92 machine-gun in the rear cockpit. 1 x 250-kg (551-lb) bomb under fuselage, 2 x 30-kg (66-lb) bombs under wings.
Engine: 1 x Nakadjima "Hikari 1", 545kW
Wingspan: 11.1 m / 36 ft 5 in
Length: 9.3 m / 30 ft 6 in
Height: 3.41 m / 11 ft 2 in
Wing area: 34.7 sq.m / 373.51 sq ft
Take-off weight: 2610 kg / 5754 lb
Empty weight: 1516 kg / 3342 lb
Max. speed: 310 km/h / 193 mph
Ceiling: 6800 m / 22300 ft
Range: 930 km / 578 miles
Armament: 3 x 7.7mm machine-guns, 1 x 250-kg bomb, 2 x 30-kg bombs