The Kyushu Q1W Tokai (Eastern Sea) was remarkable in being the first and only dedicated land-based anti-submarine aircraft developed during World War II. It was designed for an IJN requirement for an aircraft suitable for safe overwater operation and with an attack similar to that of a dive bomber aided by hydraulic slatted flaps extendable to 90 degrees to provide sufficient angle of attack. Among its ASW equipment was a rudimentary search radar in addition to a magnetic anomaly detector (MAD), it was also designed as an all-metal aircraft but shortage of strategic materials required some production examples to be built with wooden parts. The Q1W was operated from bases in Japan, China, and Formosa for protection of convoys bringing raw materials and oil from the Dutch East Indies and Malaya, however most ended up being easy pray for Allied aircraft due to poor defensive armament. Ultimately, no submarines were sunk by Tokais according to record.

The Tokai was first flown in September 1943, service entry did not begin until early 1945 due to difficulties in developing the radar. The Q1W1 was the main production variants although a number were built as the Q1W2 with a wooden rear fuselage. Meanwhile, the Q1W1-K Tokai Ren was an all-wood four-seater for electronic equipment training.