Mitsubishi A6M1 Zero Fighter

The Mitsubishi A6M Zero Fighter was the finest shipboard fighter in the world during the first year of the Pacific War. It was the first shipboard fighter capable of defeating its land-based opponents. Its world-wide fame was won in a series of astounding victories against all types of land-based and carrier-based Allied aircraft during the first six months after Pearl Harbor. It took part in every major action in which the Japanese Navy was involved, from Pearl Harbor all the way to the final B-29 assault on Japan. It became a legend in its own time for its extremely good maneuverability and its exceptionally long range. Even today, the Zero remains for the Japanese and their erstwhile enemies alike the symbol of Japanese air power during the Pacific War. Despite the fact that it was largely obsolescent by mid-1943, it remained in production until the end of the war. More Zeros were built than any other type of Japanese aircraft, a total of 10,449 being built at Mitsubishi and Nakajima factories.

In 1937, the Japanese Navy had just introduced the Navy Type 96 Carrier Fighter (Mitsubishi A5M, later known to the Allies under the code name CLAUDE) into service, but they were already looking to design its successor. On May 19, 1937, preliminary specifications for a Navy Experimental 12-Shi Carrier Fighter were submitted to both Mitsubishi and Nakajima. The number 12 indicated that the specification had been issued in the twelfth year of Showa, as the reign of Emperor Hirohito was known.

The Mitsubishi Jukogyu K.K. (Mitsubishi Heavy Industries Co Ltd) was a highly-integrated conglomerate of shipbuilding, airframe and engine manufacturing plants, with facilities located in a dozen different locations in Japan. A team led by chief engineer Jiro Horikoshi was assigned by Mitsubishi to work on the project.

In October 1937, in light of combat reports coming from China, the Japanese Navy issued a revised set of specifications. These called for a maximum speed of 310 mph at 13,100 feet, a climb to 9800 feet in 3.5 minutes, an endurance of 1.5-2.0 hours at normal rated power or 6 to 8 hours at economical cruising speed, and an armament of two 20-mm cannon and two 7.7-mm machine guns. A complete set of radio equipment had to be carried, including a radio direction finder. The maneuverability had to be at least the equal of the Mitsubishi A5M.

Nakajima thought these requirements to be completely unrealistic and pulled out of the competition on January 17, 1938. This left Mitsubish alone to try and meet the requirements of the 12-Shi project.

The design team headed by Jiro Horikoshi came up with a cantilever low-winged monoplane with a fully-retractable landing gear. The pilot was housed underneath a large transparent canopy with an excellent view both forward and aft. It was powered by a Mitsubishi Zuisei 13 (Auspicious Star) fourteen-cylinder, twin-row air-cooled radial engine, rated at 780 hp for takeoff and 875 hp at 11,810 feet. This engine was later known under the unified JNAF/JAAF designation scheme as the Ha.31/13. This engine was selected because of its light weight and small diameter, even though Horikoshi had actually favored the more powerful Mitsubishi Kinsei 46. The engine was to drive a two-bladed variable-pitch propeller.

Careful attention was paid to weight savings, and a new special aluminum alloy developed by Sumimoto was adopted.

The mockup was inspected on April 17 and July 11, 1938, and changes recommended were progressively incorporated into the design.

The first prototype was completed on March 16, 1939 at Mitsubishi's Nagoya plant. It was armed with two 7.7 mm Type 97 machine guns in the upper fuselage decking and two wing-mounted 20-mm Type 99 cannon. The aircraft was transferred to the Army's training airfield at Kagamigahara for flight testing. The aircraft took off on its first test flight on April 1, 1939 with test pilot Katsuzo Shima at the controls. The test was highly successful, the only problems noted being with the wheel brakes, the oil system and a slight tendency to vibrate. During the flight test program, the two-bladed variable-pitch propeller was replaced by a three-bladed constant speed propeller in an attempt to correct the vibration problem.

The prototype was accepted by the Navy on September 14, 1939 as the A6M1 Carrier Fighter. In the meantime, a second prototype was completed and passed its manufacturer's flight tests on October 18, 1939, and was delivered to the Navy one week later.



The speed of the A6M1 was 305 mph at 12,470 feet, which was slightly below the requirement, so on May 1, 1939, the Navy ordered Mitsubishi to install the Nakajima NK1C Sakae 12 (Prosperity) engine in the third prototype and subsequent aircraft. The Sakae 12 (Ha.35/12) engine was also a fourteen-cylinder twin-row air-cooled radial and was only slightly larger and heavier than the Zuisei despite its higher power. Mitsubishi was somewhat reluctant to do this, since the Sakae engine was a competitor's product.

The re-engined aircraft was designated A6M2. The first Sakae-powered A6M2 began flight testing on December 28, 1939. The aircraft's performance exceeded the Navy's most optimistic expectation, amply exceeding the original performance requirements which had been thought to be impossible only a few months earlier. Production of an initial service test batch of A6M2s began, and initial flight trials were completed in July of 1940. On July 31, the aircraft was formally accepted for production as the Navy Type 0 Carrier Fighter Model 11. The popular name was Reisen (which was an abbreviation for Rei Sentoki, or Zero Fighter), so chosen for its type number which was 0, standing for the last digit of the current Japanese year, which was 2600 in the Japanese calendar.

A6M2 - Rabaul

On July 21, 1940 the Japanese Navy decided to assign 15 pre-production A6M2s to the 12th Rengo Kokutai (12th Combined Naval Air Corps) for combat trials in China. In China, the A6M2 entered combat for the first time on August 19, 1940, when 12 A6M2s escorted 50 G3M2 bombers in a bombing raid over Chungking, but no enemy fighters were encountered. The Zero Fighter drew first blood on September 13, 1940 when thirteen A6M2s led by Lt Saburo Shindo attacked a force of 27 Chinese-piloted Polikarkpov I-15s and I-16s, shooting down all the Chinese aircraft with no Japanese losses. The pre-production Zero Fighters were later joined by the initial production A6M2s. In the next few months, they destroyed 99 Chinese aircraft for the loss of only two of their own to ground fire.

After over a year of use in China not one Reisen had been captured or inspected by either Chinese or American observers. Claire E. Chennault, who was a retired USAAC officer attempting to reorganize the demoralized Chinese air force, took note of this new Japanese fighter and attempted to warn the USAAF of the Zero's capabilities, but his warning was ignored and the Zero remained largely unknown in the West.

The second A6M1 crashed on March 11, 1940 when it disintegrated in midair during a test flight, the pilot being killed. Although the actual cause of this accident was never fully determined, it was thought that a wing spar might have failed. Consequently, beginning with the 22nd A6M2, a reinforcement of the rear wing spar was introduced.

Beginning with the 65th aircraft, manually upward-folding wingtips (about 20 inches long) were incorporated so that the Reisen could fit the deck elevators of the Imperial Navy's aircraft carriers. This modification resulted in a change of designation to Navy Type 0 Carrier Fighter Model 21.

The next modification affected the aileron tab balance. Beginning with the 128th Reisen, the aileron tab balance was linked to the landing gear retraction mechanism to improve high-speed control by reducing stick forces.

In order to correct an aileron flutter problem, a modified aileron tab balance was incorporated on the 192nd and subsequent A6M2.

In November 1941 the Nakajima Hikoki K.K. was instructed to begin producing the Model 21 at its Koizumi plant. This must have been especially irritating for the Nakajima company, since less than three years earlier it had thought that the Zero Fighter had been impossible to design.

When the Pacific War began on December 7, 1941, The Japanese Navy had over four hundred Zeros in service, most of them Model 21s. At Pearl Harbor, Zero Fighters flying off the carriers escorted the B5N2 torpedo bombers and D3A1 dive bombers in the first strike, and they strafed military airfields, anti-aircraft positions, and other ground installations. The Zeros caused considerable havoc on the ground at Pearl Harbor, while destroying four US aircraft in the air. Eight A6M2 fighters were lost during the raid, most of them to anti-aircraft fire.

During the first year of the Pacific War, the standard shipboard fighter serving with the US Navy was the Grumman F4F Wildcat. The A6M2 was superior to the F4F Wildcat in speed, climb rate, and maneuverability, but the Wildcat had better firepower and was more robust. In a dive the two aircraft were fairly equal, but the turning circle of the Zero Fighter was very much smaller than that of the Wildcat by virtue of its lower wing loadings.

In the first Japanese attack on Wake Island on December 8, eight Wildcats were destroyed on the ground. The remaining Wildcats fought courageously for two weeks, breaking up a number of air attacks and turning back one seaborne invasion attempt. However, they were overwhelmed by superior Japanese forces and the last two Wildcats were destroyed on December 22.

By the time of the Battle of Midway in June 1942, Wildcat pilots had evolved tactics to deal with the superior performance of the Zero. One of these was the "Thatch Weave", named for LtCmdr John S. Thatch, commander of VF-3. In this maneuver, two Wildcats would criss-cross back and forth, each one alternately covering the other's tail. Whenever possible Wildcat pilots tried to get above their opponents, so that they could then dive through the enemy formation in a firing pass, continuing their dive until they were able to zoom-climb back up to a favorable altitude for another attack. Efforts were made to avoid close-in dogfights, where the Zero clearly had the advantage.

The initial attack on the Philippines was staged by bombers and fighters based in southern Formosa. The range performance of the Zero was such that the attacking planes must have come from aircraft carriers. On December 8, 54 G4M1s and 54 G3M2s escorted by 84 A6M2s staged a raid on Clark Field. Even though Pearl Harbor had been attacked the day before, the American aircraft were still not yet dispersed and few American fighters were up in the air. Total surprise was achieved and 15 US aircraft were destroyed in the air and fifty aircraft destroyed on the ground, essentially crippling US air power in the Philippines in a single day. The first US aircraft shot down over the Philippines was a Curtiss P-40, destroyed that day by a Zero flown by Petty Officer Saboro Sakai. This was his third kill, Sakai having gotten two aircraft in China. Sakai show down the first B-17 two days later. By December 13, the US air forces were essentially gone, and the A6M2s reverted to strafing and ground support. The Zero had established air superiority in only three days.

The Zero Fighter achieved perhaps its greatest success in the Duch East Indies campaign. In about three months, a force of 200 A6M2s defeated all comers, including Brewster Model 339 Buffaloes, Curtiss-Wright CW-21Bs, Curtiss Hawk 75A-7s, and Curtiss P-40s that were thrown against it by the Dutch, British, American, and Australian forces. These fighters were no match for the Reisens, and on March 8, 1942 the Dutch were forced to capitulate.

The Zeros then turned towards New Guinea and the Solomons. During this campaign, the Reisen consistently mastered the Curtiss P-40s and the Bell P-39s and P-400s that the Allies threw against them. The Airacobra was no match for the Zero in air-to-air combat, and Saburo Sakai regarded the P-39 as a relatively easy "kill" for a pilot of any experience.

The only bright spot during these dark days was the American Volunteer Group (AVG), better known as the Flying Tigers. They were first in battle on December 20, 1941 during a Japanese raid on Kunming. The P-40s flown by the AVG were faster than the Zero in level flight, but were much less maneuverable. It was soon concluded that it was suicide to try and out-maneuver a Zero, and AVG pilots found that they were able to take advantage of the superior diving speed and ruggedness of their P-40s. The tactics that most often achieved success were to first make sure the P-40s had a height advantage, dive down on the Zeroes, shoot, and then run as fast as you could. By the time that the AVG was absorbed into the 14th Air Force in early July of 1942, they had been credited with 286 Japanese aircraft destroyed in the air as against 13 pilots killed in aerial action

The Zero Fighter was given the code name ZEKE by Capt Frank McCoy's air intelligence team in July of 1942. However, faulty identification and lack of cooperation between various intelligence officers in the CBI theatre resulted in duplicate names being assigned to the Zero Fighter, namely BEN and RAY. However, these were soon dropped in favor of ZEKE. Nevertheless, since the Reisen's official Japanese designation was known by the Allies quite early in the war, the ZEKE code name was not often used, and the Reisen was still referred to as the Zero by Allied pilots who were still trying to figure out a counter for this outstanding warplane.

In June of 1942, a Japanese task force launched a strike against the Aleutians in an attempt to draw American forces away from the intended target of Midway. On June 3, Petty Officer Tadayoshi Koga flying from the aircraft carrier Ryujo took off in his A6M2 for an inconclusive strike against Dutch Harbor. On the way back to his carrier, he found that a couple of bullet holes had pierced his fuel tanks, and told his commanding officer that he intended to attempt an emergency landing on the bleak marshes of Akutan Island. Unfortunately, the plane flipped over on its back during the landing. Although the aircraft was only slightly damaged, Petty Officer Koga's neck was broken and he was killed. Five weeks later an American naval scouting party found the Japanese fighter upside down in the marsh, the pilot still hanging dead in his straps.

Petty Officer Koga's A6M2 was only slightly damaged, and was packed up and shipped back to the USA. This was one of the greatest intelligence finds of the Pacific War, since it enabled American intelligence to make a detailed study of the Zero which was still running wild all throughout the Pacific. Koga's Zero was repaired and reflown, and went through an exhaustive series of tests in order to gain information about its strengths and weaknesses. The tests revealed the fighter's faults and finally shattered the aura of myth which had surrounded it.

Information from these tests in the United States was quickly passed along to operational units in the Pacific which were able to improve their tactics against the nimble Zero which had ruled the Pacific skies for the first six months of the Pacific War. The tests confirmed that the Zero Fighter had an excellent climb rate, and could easily outclimb both the F4F Wildcat and the Curtiss P-40. Its range of more than 1200 miles was far superior to that of any other Allied fighter then available. The tests also confirmed that the Zero was indeed the most maneuverable carrier-based fighter in the world, and that it was suicide to try and out-maneuver it, especially at low speed. However, the maneuverability of the Zero deteriorated rapidly as the speed increased. At high speeds, the ailerons stiffened and became extremely difficult to move. In addition, tests revealed that the wings had structural problems which prevented the Zero from being dived at high speeds. In combat, a pursuing Zero could often be escaped by diving at the maximum possible speed and by rolling either right or left, the Zero being unable to follow. The rule for an Allied pilot was to keep his speed as high as possible during combat and never, never try to out-maneuver a Zero while at low speed. The Zero Fighter lacked any armor protection for the pilot, did not have any self-sealing fuel tanks, and had no onboard fire extinguishing equipment. A superficial hit would often cause the aircraft to catch fire.

The final air battles fought by the A6M2 were on October 26, 1942 during the Battle of Santa Cruz. After that time, the A6M2 was superseded by the A6M3 version of the Reisen, and A6M2s were relegated to second-line units and training outfits. Many of these obsolete A6M2s were brought back to operational status and expended in kamikaze attacks in the last year of the war.

Specification of A6M2 Navy Type 0 Carrier Fighter Model 21:

One Nakajima NK1C Sakae 12 fourteen cylinder air-cooled radial, rated at 940 hp for takeoff, 950 hp at 13,780 feet.

Performance: Maximum speed 331 mph at 14,930 feet. Cruising speed 207 mph. Initial climb rate 4517 feet per minute. Climb to 19,685 feet in 7 minutes 27 seconds. Service ceiling 32,810 feet. Normal range 1160 miles. Maximum range 1930 miles. Radius of turn with entry speed of 230 mph was 1118 feet. Entering a 180 degree steep turn with an entry speed of 230 mph, the fighter could complete the turn in 5.62 seconds, with an exit speed from the turn of 189 mph. At slower speeds, the turning radius was 612 feet. Normal positive g-load factor was 7g, with a safety factor of an additional 1.8g. Normal negative g-load factor was 3.5g, with a safety factor of an extra 1.8g.

Dimensions: Wingspan 39 feet 4 7/16 inches, length 29 feet 8 11/16 inches, height 10 feet 0 1/16 inches, wing area 241.5 square feet. Weights: 3704 pounds empty, 5313 pounds loaded, 6164 pounds maximum. Fuel capacity: Internal fuel capacity was 114 Imp gall. One 72.6 Imp. gall drop tank could be carried underneath the fuselage. Armament: Two 7.7-mm Type 97 machine guns in the fuselage decking and two 20-mm Type 99 cannon in the wings. Two 132-pound bombs could be carried on underwing racks.