Chief Engineer 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 12-Shi 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:
- 300 mph at 13,000', 311 mph at 13,125' / 4,000 m
- climb to 9,840' / 10,000' / 3,000 m in 9 minutes 30 seconds
- wingspan of no more than 12 m in length to fit the elevators on the Imperial Japanese Navy's carriers
- take off within 230' / 70 m with a 40' per second / 27 knots head wind
- armament of two 7.7 mm machine guns and two 20 mm cannons
- carry two 132 lb / 60 kg bombs
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 wing root.
Another weakness of the A6M Zero is that the pilot had no armor until very late models.
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 removable.
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.
The Sakae 12 engine resulted in the the carburetor intake being made integral in the cowling and placed in the lower part of it.
At the rear the glass panels were shortened.
The A6M2 Model 11s were tested on the Soryu in June 1940. It exceeded all expectations but it was found that the wing tips could sustain damage while being moved on the elevators. The Model 21 was designed with 20" on each end of the wing being able to fold upwards to make for more room on the elevators.
Originally some A6M2s in the field were converted in 1942 to two seaters to be used for reconnaissance and command duties.
Specifications for a dedicated trainer was given in 1943. Dai-Nijuichi Kaigun Kokoshu (21st Naval Air Depot) designed the A6M2-K.
The instructor was behind the student. The trainer's seat was where the radio and other equipment was located. The student's part of the cockpit was permanently open.
Dual controls were installed. The fixed tail wheel was larger than the A6M fighters. Wheel covers and the wing cannons were removed to save weight.
A stability fin was added just in front of the horizontal stabilizer.
Later models of the A6M3 had the folding wingtips not installed.
Nakajima produced the Sakae engine which had a two stage supercharger. The engine was longer and required the firewall to the rear by 8" / 20 cm. This caused the fuel tank to have to be reduced in size.
The larger engine resulted in changing the cowling to be more rounded and larger. Propeller was slightly larger.
The first two A6M3s produced had the folding wingtips but they were removed in the hopes to increase speed. This was to compensate for the heavier engine. It was hoped that the shorter wings would make the A6M3 more maneuverable, but this didn't happen.
In honor of Air Force General "Hap" Arnold the A6M3 Model 32 was called the "Hap." However, he did not appreciate the gesture and ordered the designation to be changed to "Hamp." After captured examples of the Model 32 were captured the name was revised to Zeke 32.
The A6M5 was to be a temporary expedient until the replacement carrier based fighter, Mitsubishi A7M Reppu, was developed. As the A7M failed the A6M5 ended up being the most produced of the A6M series.
It was to be simplified for production and increase the diving speed. A heavier gauge metal was used in the wings. Diving speed was increased to 410 mph.
A6M6, A6M7, A6M8
Mitsubishi tried to improve the capabilities of the A6Ms with the A6M6, A6M7, and A6M8. But due to United States bombing campaign it was very difficult on industry.
Speed and Range Comparison