In the early 1930s, the Imperial Japanese Navy became interested in the concept of two-seat fighters, as popular with foreign air-arms, ordering a prototype of the Nakajima NAF-1 6-Shi two-seat fighter in 1931.[1] Although the NAF-1 was unsuccessful,[1] the Navy's interest in two-seat fighters continued, and in 1933, it requested new two-seat carrier-based fighter designs from Mitsubishi and Nakajima.
Mitsubishi's design, designated the Ka-8 by the company, and the Mitsubishi Experimental 8-Shi Two-seat Fighter by the Navy, was a single-engined biplane of mixed wood and metal construction. Its single-bay equal-span staggered wings had duralumin spars, with wooden ribs and fabric covering. The fuselage structure was made of welded steel tube with fabric covering, with pilot and gunner sitting in tandem in open cockpits. Two fixed forward-firing machine guns were operated by the pilot, with a single flexibly mounted machine gun in the rear cockpit. A twin tail was fitted, and the aircraft had a fixed tailwheel undercarriage. Powerplant was a single Nakajima Kotobuki, a licence-built Bristol Jupiter radial engine, driving a two-blade propeller.[2]
The first of two prototypes was completed in January 1931, with both prototypes being delivered to the Navy for formal testing later in the year. The second prototype broke up during diving tests at Yokosuka on 16 September 1934. While the pilot escaped by parachute, the observer in the rear seat was killed. This accident caused testing of the surviving prototype to be abandoned, with the Nakajima contender, the NAF-2, also being rejected, with the Navy abandoning the two-seater carrier fighter category.[2]