The Aichi AB-4 was a Japanese flying boat of the 1930s.
A single engine biplane, the AB-4 was intended to carry out night reconnaissance for the Imperial Japanese Navy.
Six were built and accepted into service as the Experimental 6-Shi Night Reconnaissance Flying boat, three of which were converted to civil transports.
In 1931, the Imperial Japanese Navy instructed the Aichi Tokei Denki Seizo KK, who had been involved in aircraft manufacture, particularly for the Navy, since 1920, to design a small catapult launched night reconnaissance aircraft, intended to observe nocturnal shipping movements, spot naval gunfire during night engagements and to direct friendly submarines.
The resulting design, designated AB-4 by Aichi was a single-engine pusher biplane flying boat of all-metal construction.
Its single-bay wings folded backwards for storage aboard ship, while its crew of 3 were housed in open cockpits.
It was powered by a single Gasuden Urakaze water-cooled six-cylinder inline engine driving a two blade propeller.
The first prototype flew in May 1932, and while handling was generally good, it had poor control during take-off and landing, and a poor view for the pilot.
Despite this, a further five prototypes were ordered for evaluation.