Jiro Horikoshi designed the Mitsubishi A6M as a replacement for the A5M. The A5M outperformed all of its rivals in China leading to the belief that a highly maneuverable fighter was better.
A requirement for a new fighter was issued on January 17, 1938, to Nakajima and Mitsubishi. Convinced it was impossible to meet the requirements, Nakajima withdrew. The requirements were for a fighter that could go 300 mph at 13,000' and climb to 10,000' in 9 1/2 minutes.
Mitsubishi was developing the 11-Shi bomber at the time and didn't want to divert resources to a new fighter that it too thought was impossible to build. In exchange for letting Mitsubishi drop the 11-Shi project, the Imperial Japanese Navy talked Mitsubishi into developing the "impossible" fighter.
Once testing was complete the Imperial Japanese Navy gave it its designation, the A6M1 Rei Shiki Sento Ki (Type 0 Carrier borne Fighter).
The Zeke name came from the Japanese year 2600 that it was designated.
The first two prototypes had the Mitsubishi Zuisei 13 (875 HP) engine installed. On the third prototype carried the Nakajima Sakae 12 (950 HP) engine. The Sakae 12 was selected and it resulted in the need for making the A6M even lighter so armor plate and self sealing fuel tanks were not included in the initial design.
The engines were very good, but as the war progressed quality declined.
The undercarriage of the A6M was wide and sturdy.
One of the main weaknesses of the A6M Zero was that it didn't have self sealing fuel tanks.
There were three fuel tanks, one in front of the pilot and one in each wingroot.
Another weakness of the A6M Zero is that the pilot had no armor.
In the rear of the fuselage was a canvas floatation bag in the case of a ditching at sea.
The center section was made an integral part of the wing which save weight and aided in maintenance. The front and rear sections of the fuselage were removeable.
To make the A6M as light as possible the wing was developed to be in one piece and made from lightweight Extra-Super Duralumin.
The prototype had two 7.7 mm Type 97 machine guns that were in the top of the fuselage with cocking mechanisms coming out the instrument panel.
Two 20 mm Oerlikon cannons (license built by Dai-Nihon Heiki Company as Type 99s) were in the wings. These were outside the landing gear.
Speed and Range Comparison