The Mitsubishi A6M Reisen ("ree-sin," Japanese for Zero Fighter) was the symbol of Japanese air power during World War II. Mitsubishi designed the Zero fighter but co-produced the airplane with Nakajima. The two companies built more than 10,000 Zeros between March 1939 and August 1945. Design work began in 1937 when the Japanese Navy staff directed Mitsubishi and Nakajima to submit proposals for a new aircraft to replace the Mitsubishi A5M carrier fighter.