The Aichi AB-4 was a Japanese flying boat from the 1930s.
Designed as a single-engine biplane, the AB-4 served the Imperial Japanese Navy for night reconnaissance missions.
Six units were constructed and entered service as the Experimental 6-Shi Night Reconnaissance Flying Boat, with three later converted into civil transports.
In 1931, the Imperial Japanese Navy commissioned Aichi Tokei Denki Seizo KK, an aircraft manufacturer since 1920, to create a compact, catapult-launched aircraft for night reconnaissance.
This aircraft was intended to track nocturnal shipping activities, aid in spotting naval gunfire during night battles, and direct friendly submarines.
The design that emerged, the AB-4, was an all-metal, single-engine pusher biplane flying boat.
It featured single bay wings that could fold back for shipboard storage and accommodated a crew of three in open cockpits.
A Gasuden Urakaze water-cooled six-cylinder inline engine, driving a two-bladed propeller, powered the aircraft.
The first prototype took flight in May 1932 and exhibited generally good handling but suffered from poor control during take-off and landing, as well as limited visibility for the pilot.
Nevertheless, an additional five prototypes were commissioned for further evaluation.
