History
Once the Japanese Pacific "empire” had expanded to its greatest extent in mid-1942, the Navy General Staff realized that their supply lines -- basically consisting of slow, plodding “marus” usually sailing independently and not in convoy -- were extremely vulnerable to American submarines, which patrolled almost unopposed throughout the empire.
The Japanese considered the submarine mainly a weapon to be used against enemy warships. But American submarines were used primarily as commerce destroyers like the German U-Boats, and took such a toll of Japanese shipping that more and better aircraft were required for anti-submarine duties. In 1942, the Watanabe Tekkosho, later Kyushu Hokoki, was assigned the task of developing a specialized aircraft for this role. A design was quickly developed, the Q1W1, which appeared as a three-seat twin engine monoplane emphasizing endurance over speed.