In 1932, the Imperial Japanese Navy issued a requirement for a new carrier-borne attack aircraft. Aichi, Mitsubishi and Nakajima responded to this requirement and each built a prototype. None of these aircraft were deemed satisfactory, and the service thus issued in 1934 a new requirement, 9-Shi, for a more capable aircraft to replace the obsolescent Yokosuka B3Y.
The B4Y was designed by Sanae Kawasaki at the First Naval Air Technical Arsenal at Yokosuka. Regarded only as an interim type, the Navy wanted a torpedo bomber offering performance comparable to the Mitsubishi A5Mmonoplanefighter. The result was a biplane with fixed landing gear and an all-metal structure with metal or fabric skin. To speed development and production, the B4Y utilised the wings from the Kawanishi E7K. The B4Y1 was also the first Navy carrier attack aircraft to utilize an air-cooled engine, as the prototype that was equipped with the Nakajima Hikari 2 radial engine performed better than its competitors.[2]
The crew of three occupied two cockpits. The pilot in the open front cockpit and the other two crewmen, (navigator and radio operator/gunner), in the enclosed rear cockpit.
Although primarily used as a carrier-based aircraft, the B4Y1 was also used as a land-based bomber on occasion. In 1940, the Nakajima B5N replaced the B4Y1 as the primary carrier attack aircraft, though the B4Y1 did remain in service as an advanced trainer, and flew from Hōshō and Unyō until 1943.
Before its replacement, the B4Y1 had flown during the Second Sino-Japanese War and served at the Battle of Midway during June 1942, where eight of them were operated from Hōshō.[3] It was one of these planes from Hōshō which took photographs of the burning Hiryū on 5 June 1942.[4]
English Translation of Kojinsha No. 6 Warships of the Imperial Japanese Navy.
Lawrence, Joseph (1945). The Observer's Book Of Airplanes. London and New York: Frederick Warne & Co.
Parshall, Jonathan; Tully, Anthony (2005). Shattered sword : the untold story of the Battle of Midway. Washington, D.C: Potomac Books. ISBN1-57488-923-0. OCLC60373935.
1 X as second letter is for experimental aircraft or imported technology demonstrators not intended for service,
2 Hyphenated trailing letter (-J, -K, -L, -N or -S) denotes design modified for secondary role, 3 Possibly incorrect designation, but used in many sources
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