Mitsubishi A6M Zero — The Mitsubishi (Mitsubishi Heavy Industries Ltd. or MHI) A6M Zero was a long range fighter aircraft operated by the Imperial Japanese Navy Air Service (IJNAS) from 1940 to 1945. The A6M was designated as the Mitsubishi Navy Type 0 Carrier Fighter, and also designated as the Mitsubishi A6M Rei-sen and Mitsubishi Navy 12-shi Carrier Fighter. The A6M was usually referred to by the Allies as the “Zero”, from the ‘Navy Type 0 Carrier Fighter’ designation. The official Allied reporting name was Zeke.
When it was introduced early in World War II, the Zero was considered the most capable carrier based fighter in the world, combining excellent maneuverability and very long range. In early combat operations, the Zero gained a legendary reputation as a “dogfighter”, achieving the outstanding kill ratio of 12 to 1, but by mid-1942 a combination of new tactics and the introduction of better equipment enabled the Allied pilots to engage the Zero on more equal terms. The IJNAS also frequently used the type as a land based fighter. By 1943, inherent design weaknesses and the increasing lack of more powerful aircraft engines meant that the Zero became less effective against newer enemy fighters that possessed greater firepower, armor, and speed, and approached the Zero’s maneuverability. Although the Mitsubishi A6M was outdated by 1944, it was never totally supplanted by the newer Japanese aircraft types. During the final years of the War in the Pacific, the Zero was used in kamikaze operations. In the course of the war, more Zeros were built than any other Japanese aircraft.
Design and development
The Mitsubishi A5M fighter was just starting to enter service in early 1937 when the Imperial Japanese Navy started looking for its eventual replacement. In May they issued specification 12-Shi for a new aircraft carrier-based fighter, sending it to Nakajima and Mitsubishi. Both firms started preliminary design work while they awaited more definitive requirements to be handed over in a few months.
Based on the experiences of the A5M in China, the Navy sent out updated requirements in October. The new requirements called for a speed of 500 km/h at 4000 m and a climb to 3000 m in 3.5 min. They needed an endurance of two hours at normal power, or six to eight hours at economical cruising speed (both with drop tanks). Armament was to consist of two 20 mm cannon and two 7.7 mm machine guns and two 30 kg or 60 kg bombs. A complete radio set was to be mounted in all airplanes, along with a radio direction finder for long-range navigation. The maneuverability was to be at least equal to that of the A5M, while the wing span had to be less than 12 m to fit on the carriers.
Nakajima’s team thought the new requirements were impossible to achieve and pulled out of the competition in January. Mitsubishi’s chief designer, Jiro Horikoshi, felt that the requirements could be met, but only if the aircraft could be made as light as possible. Every weight-saving method was used; the designers made extensive use of the new duralumin alloy (see below). With its low-wing cantilever monoplane layout, retractable wide-set landing gear and enclosed cockpit, the design was not only much more modern than any the Navy had used in the past, it was one of the most modern in the world.
The A6M was a more spartan design than contemporary western aircraft. Unlike other contemporary fighters, there was no armor plate to protect the single pilot, and no self-sealing fuel tanks. Most of the airplane was built of T-7178 aluminum, a top-secret variety developed by the Japanese for the purpose. It was lighter and stronger than the normal aluminum used at the time, but more brittle. The Zero had a fairly high-lift, low-speed wing with a very low wing loading, giving it a very low stalling speed of well below 60 knots. This is the reason for the phenomenal turning ability (imposition of g-load on the wings in a turn before an accelerated stall occurs) of the airplane, allowing it to turn more sharply than any Allied fighter of the time. Roll rate is enhanced by servo tabs on the ailerons which deflect opposite to the ailerons and make the control force much lighter. The disadvantage is that they reduce the maximum roll effect at full travel. At 160 mph (260 km/h) the A6M2 had a roll rate of 56 degrees per second. Because of wing flexibility, roll effectiveness dropped to near zero at about 300 mph indicated airspeed. The American military discovered many of the A6M’s unique attributes when they recovered a mostly intact specimen at Alaska. The Japanese pilot had strayed too far away from base and hoped to make an emergency landing in US territory but the plane flipped over and his neck was broken
The pre-series A6M2 Zero became known in 1940-41, when the fighter destroyed 266 confirmed aircraft in China. At the time of Pearl Harbor, there were 420 Zeros active in the Pacific. The carrier-borne Model 21 was the type encountered by the Americans, often much further from its carriers than expected, with a mission range of over 1600 statute miles (2,600 km). The Zero fighters were superior in many aspects of performance to all Allied fighters in the Pacific in 1941 and quickly gained a great reputation. However, the Zero failed to achieve complete air superiority due to the development of suitable tactics and new aircraft by the Allies. During WWII the Zero destroyed at least 1,550 American planes.
Designed for attack, the Zero gave precedence to maneuverability and firepower at the expense of protection — most had no self-sealing tanks or armor plate — thus many Zeros were lost too easily in combat along with their pilots. Ironically, up to the initial phases of the Pacific conflict, the Japanese trained their aviators far more strenuously than their Allied counterparts. However, unexpectedly heavy pilot losses at the Coral Sea and Midway made them difficult to replace.
With the extreme agility of the Zero, the Allied pilots found that the appropriate combat tactic against Zeros was to remain out of range and fight on the dive and climb. By using speed and resisting the deadly error of trying to out-turn the Zero, eventually cannon or heavy machine guns could be brought to bear and a single burst of fire was usually enough to down the Zero. These tactics, known as boom-and-zoom, were successfully employed in the CBI against similarly maneuverable Japanese Army aircraft such as the Ki-27 and Nakajima Ki-43 by the Flying Tigers (American Volunteer Group). AVG pilots were trained to exploit the advantages of their P-40s; very sturdy, heavily armed, generally faster in a dive and in level flight at low altitude, with a good rate of roll.
Another important maneuver was called the “Thach Weave,” named for the man that invented it, then-Lt Cdr John S. “Jimmy” Thach. It required two planes, a leader and his wingman, to fly about 200 feet apart. When a Zero would latch onto the tail of one of the fighters, the two planes would turn toward each other. If the Zero followed its original target through the turn, it would come into a position to be fired on by his target’s wingman. This tactic was used with spectacular results at the Battle of the Coral Sea and at the Battle of Midway, helping make up for the inferiority of the US planes until new aircraft types were brought into service. When the powerful Grumman F6F Hellcat, Vought F4U Corsair and Lockheed P-38 appeared in the Pacific theater, the A6M with its low-powered engine lost its competitiveness. The US Navy’s 1:1 kill ratio suddenly jumped to better than 10:1. While the Hellcat and Corsair are generally considered to better all-around than the Zero, US successes also had to do with the increasingly inexperienced Japanese aviators. Nonetheless, until the end of the war, in competent hands, the Zero could still be deadly. Because of the scarcity of high-powered aviation engines and some problems with planned successor models, the Zero remained in production until 1945, with over 11,000 of all types produced.