The Mitsubishi A6M Zero was a lightweight fighter aircraft operated by the Imperial Japanese Navy Air Service (IJNAS) from 1940 to 1945. The origin of its official designation was that "A" signified a fighter and "6" for the sixth model built by Mitsubishi ("M"). The A6M was usually referred to by the Allies as the "Zero"—a name that was frequently misapplied to other Japanese fighters, such as the Nakajima Ki-43—as well as other codenames and nicknames, including "Zeke", "Hamp" and "Hap".
Its history mirrored that of the Empire of Japan in World War II. When it was introduced, the Zero was the best carrier-based fighter in the world and it was greatly feared by Allied pilots. The IJNAS also frequently used the type as a land-based fighter. A combination of excellent maneuverability and very long range made it one of the finest fighters of its era. In early combat operations, the Zero gained a legendary reputation, outclassing its contemporaries. Later, design weaknesses and the increasing scarcity of more powerful aircraft engines meant that the Zero became less effective against newer fighters. By 1942, due to the evolution of new tactics and techniques, Allied pilots were able to engage the Zero on more equal terms. By 1943, American and British manufacturers were producing fighters with greater firepower, armor, and speed, and approaching the Zero's maneuverability. The Mitsubishi A6M was outdated by 1944, but remained in production. During the final years of the War in the Pacific, the Zero was utilized in kamikaze operations.
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. Most of the airplane was built of T-7178 aluminum, a top-secret aluminum alloy developed by the Japanese just for this aircraft. It was lighter and stronger than the normal aluminum used at the time, but more brittle. In addition, no armor was carried for the pilot, engine or other critical points of the aircraft, and the self-sealing fuel tanks that were becoming common at the time were also left off. This made the Zero lighter and more agile than most other aircraft at the start of the war, but that also made it prone to catching fire and exploding when struck by enemy rounds.
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 Zero had a fairly high-lift, low-speed wing with a very low wing loading; combined with the light weight this gave it a very low stalling speed of well below 60 knots. This is the reason for the phenomenal turning ability 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 official Allied code name was Zeke in keeping with the practice of giving boys' names to Japanese fighters, girls' names to bombers, bird names to gliders and tree names to trainers. The reason for choosing Zeke as a code name for the Mitsubishi A6M is uncertain. When in 1942 the Allied code for Japanese planes was introduced Zeke may have been thought an appropriate choice. Later two variants of the fighter, not immediately identified as such, received their own code names: the A6M2-N (floatplane version of the Zero) was called Rufe and the A6M3-32 variant was called Hamp.
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 World War II, the Zero destroyed at least 1,550 American aircraft. The Japanese ace Saburo Sakai described how the resilience of early Allied aircraft was a factor in preventing the Zeros from attaining total domination:
I had full confidence in my ability to destroy the Grumman and decided to finish off the enemy fighter with only my 7.7mm machine guns. I turned the 20mm. cannon switch to the 'off' position, and closed in. For some strange reason, even after I had poured about five or six hundred rounds of ammunition directly into the Grumman, the airplane did not fall, but kept on flying. I thought this very odd—it had never happened before—and closed the distance between the two airplanes until I could almost reach out and touch the Grumman. To my surprise, the Grumman's rudder and tail were torn to shreds, looking like an old torn piece of rag. With his plane in such condition, no wonder the pilot was unable to continue fighting! A Zero which had taken that many bullets would have been a ball of fire by now.
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. During 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.
The American military discovered many of the A6M's unique attributes when they recovered a mostly intact specimen on Akutan Island in the Aleutians. Flight Petty Officer Tadayoshi Koga was losing fuel and hoped to make an emergency landing but the Zero flipped over and the pilot's neck was broken. The relatively undamaged fighter was recovered and shipped to North Air Station, North Island, San Diego. Subsequent testing of the repaired A6M revealed not only its strengths but also deficiencies in design and performance.
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 China Burma India Theater (CBI) against similarly maneuverable Japanese Army aircraft such as the Nakajima Ki-27 and 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 fighters, a leader and his wingman, to fly about 200 ft (60 meters) apart. When a Zero latched 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 U.S. fighters 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 U.S. Navy's 1:1 kill ratio suddenly jumped to better than 10:1. While the Hellcat and Corsair are generally considered better all-around than the Zero, U.S. 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.
While the Navy was testing the first two prototypes, they suggested that the third be fitted with the 940 hp (700 kW) Nakajima Sakae 12 engine instead. Mitsubishi had its own engine of this class in the form of the Kinsei, so they were somewhat reluctant to use the Sakae. Nevertheless when the first A6M2 was completed in January 1940, the Sakae's extra power pushed the performance of the plane well past the original specifications.
The new version was so promising that the Navy had 15 built and shipped to China before they had completed testing. They arrived in Manchuria in July 1940, and first saw combat over Chungking in August. There they proved to be completely untouchable by the Polikarpov I-16s and I-153s that had been such a problem for the A5Ms currently in service. In one encounter 13 Zeros shot down 27 I-15s and I-16s in under three minutes without loss. After hearing of these reports the Navy immediately ordered the plane into production as the Type 0 Carrier Fighter, Model 11.
Reports of the Zero's performance filtered back to the US slowly. There they were dismissed by most military officials, who felt it was impossible for the Japanese to build such an aircraft.
After the delivery of only 65 planes by November 1940, a further change was worked into the production lines, which introduced folding wingtips to allow them to fit on the aircraft carriers. The resulting Model 21 would become one of the most produced versions early in the war. When the lines switched to updated models, 740 Model 21s were completed by Mitsubishi, and another 800 by Nakajima. Two other versions of the Model 21 were built in small numbers, the Nakajima-built A6M2-N "Rufe" floatplane (based on the model 11 with a slightly modified tail), and the A6M2-K two-seat trainer of which a total of 508 were built by Hitachi and the Sasebo Naval Air Arsenal.
In late 1941, Nakajima introduced the Sakae 21, which used a two speed supercharger for better altitude performance, and increased power to 1,130 hp (840 kW). Plans were made to introduce the new engine into the Zero as soon as possible.
The new Sakae was slightly heavier and somewhat longer due to the larger supercharger, which moved the center of gravity too far forward on the existing airframe. To correct for this the engine mountings were cut down by 8 inches (200 mm), moving the engine back towards the cockpit. This had the side effect of reducing the size of the main fuel tank (located to the rear of the engine) from 518 litres to 470 litres.
The only other major changes were to the wings, which were simplified by removing the Model 21's folding tips. This changed the appearance enough to prompt the US to designate it with a new code name, Hap. This name was short-lived, as a protest from USAAF commander General Henry "Hap" Arnold forced a change to Hamp. Soon after, it was realized that it was simply a new model of the Zeke. The wings also included larger ammunition boxes, allowing for 100 rounds for each of the 20 mm cannon.
The wing changes had much greater effects on performance than expected. The smaller size led to better roll, and their lower drag allowed the diving speed to be increased to 360 knots (670 km/h). On the downside, maneuverability was reduced, and range suffered due to both decreased lift and the smaller fuel tank. Pilots complained about both. The shorter range proved a significant limitation during the Solomons campaign of 1942.
The first Model 32 deliveries began in April 1942, but it remained on the lines only for a short time, with a run of 343 being built.
As the airframe was reverted from the Model 32 and the engine remained the same, this version received the navy designation Model 22, while Mitsubishi called it the A6M3a. The new model started production in December, and 560 were eventually produced. This company constructed some examples for evaluation, armed with 30 mm Type 5 Cannon, under denomination of A6M3b (model 22b).
The A6M5 was a modest update of the A6M3 Model 22, with nonfolding wing tips and thicker skinning to permit faster diving speeds, plus an improved exhaust system (four pipes on each side) that provided an increment of thrust. Improved roll-rate of the clipped-wing A6M3 was now built in.
The A6M5 could travel at 540 km/h and reach a height of 8000 meters in nine minutes, 57 seconds. Other variants are the night fighter A6M5d-S (modified for night combat, armed with one 20 mm type 99 cannon, inclined back to the pilot's cockpit) and A6M5-K "Zero-Reisen"(model l22) tandem trainer version, also manufactured by Mitsubishi.
A number of flyable Zero airframes exist; most have had their engines replaced with similar American units; only one, the Planes of Fame Museum's example, bearing tail number "61-120" (see external link below) has the original Sakae engine. Although not truly a survivor, the "Blayd" Zero is a reconstruction based on templating original Zero components recovered from the South Pacific; a small fraction of parts in the reconstruction are from the original Zero landing gear. The aircraft is now on display at the Fargo Air Museum in Fargo, North Dakota.
The rarity of flyable Zeros accounts for the use of single-seat T-6 Texans, modified externally and painted in Japanese markings, to stand in for the fighter in the films Tora! Tora! Tora!, The Final Countdown, and many other television and film depictions of the aircraft.