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The Aichi D1A Diver Bomber 'Susie' was a carrier dive-bomber based on the Heinkel He 66 that saw service with the Japanese Navy during the 1930s.
The Japanese Navy became interested in dive bombers very early on, and issued 6-Shi and 7-Shi specifications, both of which resulted in experimental Nakajima aircraft. Unfortunately neither design was suitable for service and in 1933 a new 8-Shi specification for a two-man carrier dive bomber was issued. This specified higher performance figures than the earlier aircraft, combined with a strong structure and good manoeuvrability. Nakajima, Aichi and the Navy's own internal team at Dai-Ichi Kaigun Koku Gijitusho were each asked to produce a design.
Nakajima produced the D2N, also a biplane, but this performed badly in the contest. The Dai-Ichi Kaigan Koku design was produced as the Experimental Kusho 8-Shi Special Bomber (D2Y1), but also proved to have problems.
Aichi already had a partnership in place with Heinkel, and in 1931 asked them to develop a dive bomber. This had to be able to carry a 550lb bomb load and operate with wheels or floats. Heinkel produced the He 50,a two-bay biplane with a mixed welded steel tube and wooden structure and a fabric covering. The first prototype had a 390hp Junkers L 5 engine, but this wasn't powerful enough and the second used a 490hp Siemens Jupiter VI (SAM-22B) radial engine. These aircraft were produced during 1931. A single prototype was then exported to Japan, with the designation Heinkel He 66. The basic design was also accepted for German service as the He 50, and a batch of He 66s was even produced for Nationalist China (although never delivered).
Aichi modified the design to make it more suited for Japanese needs. This involved replacing the Siemens engine with a 560hp Nakajima Kotobuki 2 Kai 1 nine-cylinder air-cooled radial engine and the production of a stronger undercarriage capable of dealing with carrier landings.
The first prototype of the Aichi Special Bomber (Aichi designation AB-9) was submitted to the Navy, and underwent tests against the Nakajima D2N and the Kusho D2Y1. It outperformed both designs, and late in 1934 the type was ordered into production as the Navy Type 94 Carrier Bomber or Aichi D1A1.
The D1A1 was a two bay biplane of mixed welded steel tube and wooden structure with a fabric covering. The Nakajima engine was given a Townend ring. The wings were swept back by 5 degrees and a fixed tailwheel was installed. It was armed with two fixed forward firing 7.7mm Type 92 machine guns and one flexibly mounted 7.7mm Type 92 gun. It could carry two 66lb bombs under the wings and one 551lb on a swing--down mounting under the fuselage. A total of 162 aircraft were built, 118 with the 580hp Nakajima 2 Kai 1 and 44 with the Kotobuki 3.
The D1A2 was designed in 1935. It had a 730hp Nakajima Hikari 1 nine-cylinder air-cooled radial engine in a NACA cowling, an improved wind shield and streamlined wheel spats. The prototype was completed in the autumn of 1936 and it entered production as the Navy Type 96 Carrier Bomber (D1A2). The D1A2 was produced in larger numbers than the D1A1, with a total of 428 built between 1936 and 1940. The extra engine power increased the aircraft's top speed by 18mph and shaved over a minute and a half off the climb time to 9,845ft.
Both the D1A1 and D1A2 saw service at the start of the Second Sino-Japanese War. Over its career the D1A was used on the carriers Akagi, Kaga and Ryujo and with the 12th, 13th, 14th and 15th Kokutais of land based aircraft.
The D1A1 had largely been phased out by 1941, although a few remained in training units.
The D1A2 had a slightly longer career In 1937 it became infamous around the world after the type was used to sink the American gunboat Panay in the Yangtze River on 12 December 1937. 68 were still in use with second line units in December 1941, and it was given the Allied code name Susie. By this point the aircraft was obsolete, and it soon disappeared from even these units. The original Heinkel He 50 actually had a longer active career, and was used with night harassment units in 1943-44.
D1A1
Engine: Nakajima 2 Kai 1
Power: 560hp
Crew: 2
Span: 37ft 3 5/8in
Length: 30ft 10 1/16in
Height: 11ft 2 13/16in
Empty weight: 3,086lb
Loaded weight: 5,291lb
Max speed: 174mph at 6,725ft
Climb Rate: 9min 30sec to 9, 845ft
Service ceiling: 7,000m
Range: 656 miles
Armament: Two fixed forward firing 7.7mm Type 92 machine guns and one flexibly mounted 7.7mm Type 92 machine gun
Bomb load: Two 66lb bombs under wings, one 551lb bomb under fuselage
D1A2
Engine: Nakajima Hikari 1 nine-cylinder air-cooled radial engine
Power: 730hp
Crew: 2
Span: 37ft 4 13/16
Length: 30ft 6 1/8in
Height: 11ft 2 1/4in
Empty weight: 3,342lb
Loaded weight: 5,512lb
Max speed: 192mph at 10,500ft
Climb Rate: 7min 51sec to 9,845ft
Service ceiling: 22,900ft
Armament: Two fixed forward firing 7.7mm Type 92 machine guns and one flexibly mounted 7.7mm Type 92 machine gun
Bomb load: Two 66lb bombs under wings, one 551lb bomb under fuselage