After the failure of a6m4, due to the continuous inability to solve the engine problem and serious backwardness of the development progress of a7m gale, which was originally scheduled to replace zero, gale failed to start mass production in 1943 and replaced zero as a new generation of Shipborne main fighter. Therefore, Mitsubishi started the development of A6M5. In order to pursue better combat performance (especially dive speed), the 904th a6m3 was used to refit into A6M5 prototype. Takahashi, a member of zero development team, was responsible for the project. The A6M5 was greatly improved, the main wing was redesigned, the wing surface skin was stronger, and the wing tip was still round, but it could not be folded. The wing is similar to a6m332, with a wingspan of 11 meters and a wing area of 21.3 square meters. In each modification of A6M5, the fuselage structure is gradually strengthened, bulletproof armor and self sealing oil tank are added, a6m3 weapons, wing oil tank and engine are retained, and each cylinder is equipped with a separate exhaust pipe to increase some additional power. In August 1943, A6M5 made its first flight. Although A6M5 weighed 200kg more than a6m3, the original Rong 21 engine continued to be used because it could not be replaced with a larger horsepower engine, but a relatively new theoretical technology was used to change the exhaust pipe under the fairing blade into a separated short pile type, Under the condition of constant horsepower, the maximum level flight speed of A6M5 at 6000 m altitude was increased to 565 km / h by waste heat exhaust thrust, and the maximum dive speed reached 660 km / h. A6M5 was put into service in the autumn of 1943