The Aichi AC-1 was an experimental 330 hp nine-cylinder air-cooled radial engine. First run in 1929, it was used to power the newly designed Aichi AB-2, a catapult-launched reconnaissance seaplane.
The AB-2 with its AC-1 engine is noted for being the first shipboard reconnaissance seaplane and engine combination designed and manufactured entirely in Japan, without foreign assistance. This was a major turning point, not only for Aichi, but for all of the other Japanese aircraft and engine manufacturers, as they no longer need rely on foreign designs.
The engine proved to be a disappointment by not performing as expected. On one test flight, an exhaust fire spread to the airframe and the aircraft was lost, and, soon after, the project ended.