While working with the Mitsubishi company, the British aircraft designer Herbert Smith designed the 2MT1 two-seat biplane torpedo bomber which flew for the first time in January 1923. It went into Japanese Navy service as the Type 13-1 carrier-borne attack aircraft or B1M1, and was followed by the 2MT2 and 2MT3 variants (also designated B1M1). The redesigned Type 13-2 was designated B1M2. The final version, the Type 13-3 or B1M3, had the company designation 3MT2 and was a three-seater. Total production was 443. The B1M was powered by a 335 kW Napier Lion or Hispano-Suiza engine according to version.
The type entered service in 1924 and served into the 1930s, 32 flying from the aircraft carriersKaga and Hōshō during the Shanghai Incident in 1932. An aircraft from Kaga was lost during an aerial engagement between an American air force adviser and demonstration pilot to the Chinese government, Robert Short, who also lost his life, and regarded as a hero defending the Chinese city against the Japanese aircraft.
From 1929, a number of surplus B1Ms were converted for civilian use, being fitted with an enclosed cabin for passengers or cargo.
Initial two seat production version powered by 336 kW (450 hp) Napier Lion engine - formal (long) navy designation Navy Type 13-1 Carrier Attack Aircraft. Company designation 2MT1, 2MT2 and 2MT3. 197 built by Mitsubishi.
Prototype two-seat torpedo bomber powered by 336 kW (450 hp) Mitsubishi Hi engine (licenced built Hispano-Suiza). One built.
Three-seat production torpedo bomber, based on 2MT5, powered by Mitsubishi Hi engine. - formal (long) navy designation Navy Type 13-2 Carrier Attack Aircraft. Company designation 3MT1. 115 built by Mitsubishi.
Improved B1M2 with revised propellor and reduction gear. Long Navy designation Navy Type 13-3 Carrier Attack Aircraft. Company designation 3MT2. 128 built by Mitsubishi and Hiro Naval Arsenal.
Mitsubishi Army Type 87 Light Bomber
Mitsubishi B1Ms used by the Imperial Japanese Army Air force.
T-1.2 Converted Aeroplane
Civil conversion of B1M. Several variations on type. Enclosed cabin for two or three passengers. Powered by original Lion or Hispano-Suiza engines or converted with licenced built Bristol Jupiterradial engine. Also known as Type 13th Year Converted Aeroplane.