The Mitsubishi Experimental 9-Shi Carrier Attack Aircraft (B4M1) was a unsuccessful design for a carrier based torpedo and standard bomber that was difficult to control and that didn't enter service.
The Navy's 7-Shi Carrier Attack aircraft had not produced a suitable design, so in February 1934 the navy began a 9-Shi contest. Mitsubishi and Nakajima were asked to produce improved designs for a carrier based attack aircraft.
Mitsubishi responded with an aircraft that was similar to their 7-Shi Carrier Attack Aircraft. The heavy Rolls-Royce Buzzard water-cool engine of the 7-Shi was replaced with a Mitsubishi 8-Shi air-cooled radial engine, and despite being very similar in size to the 7-Shi, the new aircraft was 1,300lb lighter, both when empty and loaded. The Mitsubishi engine wasn't quite as powerful as the Buzzard, but the reduction in weight meant that top speed increased by 20mph to 150mph.
The 9-Shi was similar to the 7-Shi in appearance and in size. The fuselage rear of the engine was very similar to that of the 7-Shi, but the wings of the 9-Shi had a metal framework, replacing the wood used on the 7-Shi. The rest of the fuselage had a metal structure and both wings and fuselage were fabric covered.
The main undercarriage underwent the biggest visual change (other than the engine). On the 7-Shi the lower wing had been level with the bottom of the fuselage and the main wheels were contained within streamlined spats carried close to the wing. On the 9-Shi the lower wing was mounted below the fuselage for most of its length. The centre part of the wing was angled up to join the fuselage. The wheel spats were removed and the wheels were mounted a little further from the wing, moving the fuselage further up.
The 9-Shi Carrier Attack Aircraft was designed by Hajime Matsuhara, the designer of the 7-Shi. It was developed with impressive speed, and the prototype made its maiden flight in August 1934, only six months after the Navy contest began. Its size, weight, overall configuration and performance figures were similar to that of the Fairey Swordfish, but while the Royal Navy struggled on with its biplane torpedo bomber the Japanese soon moved on. The new wings on the Mitsubishi 9-Shi weren't rigid enough, making it difficult to control. The Nakajima B4N design also failed, and the Navy decided to produce the Kusho Type 96 Carrier Attack Aircraft (B4Y1), some of which were produced by Mitsubishi. This was the last biplane aircraft to serve in a frontline combat role with the Japanese Navy, and was soon replaced by more modern and more powerful monoplane designs.
Engine: Mitsubishi 8-Shi fourteen cylinder air-cooled radial engine
Span: 48ft 6.5in
Length: 32ft 8in
Height: 12ft 11in
Empty weight: 4,409lb
Loaded weight: 8,437lb
Max speed: 150mph
Climb Rate: 14 minutes 33sec to 9,843ft
Endurance: 6hr 10min
Armament: Three 7.7mm machine guns
Bomb load: Up to 1,736lb torpedo or same weight in bombs