Mitsubishi A6M Zero Fighter

A6M1

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.

A6M2

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.

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.

A6M2-N "Rufe"

In the autumn of 1940, anticipating the possibility of a Pacific war against the United States, the Japanese Navy issued a 15-Shi specification for a single-seat fighter seaplane that would be capable of providing air cover for offensive amphibious operations in far-flung places where land bases were not yet available. At that time, the Japanese Army's Corps of Engineers was quite small and was ill-equipped for the task of building airfields in newly-conquered territories in a hurry.

The Kawanishi Kokuki K.K. (Kawanishi Aircraft Co Ltd) began work on their N1K1 project to meet this requirement, but it soon became obvious that this ambitious aircraft would not be ready in time for the upcoming war with the USA. As a temporary alternative, the Japanese Navy ordered the Nakajima Hikoki K.K. (Nakajima Aeroplane Co Ltd) to begin work on a seaplane adaptation of the Mitsubishi A6M2 Reisen (Zero Fighter) that Nakajima was also building.

Work on the project began in February of 1941. The A6M2 Model 11 with the non-folding wingtips was used as the basis. The retractable landing gear was removed and the wheel wells were faired over. A large central float was mounted, attached to the belly of the fuselage by means of a forward-sloping pylon and an aft V-strut. Two stabilizing cantilever floats were fitted underneath the outboard wings. The standard powerplant and armament of the A6M2 were retained. In order to provide the additional aerodynamic stability required by the presence of the large float, the area of the vertical tail surfaces had to be increased and a small ventral fin was added. Because the main pylon had taken up the space previously reserved for the ventral drop tank, an auxiliary fuel tank was installed in the float itself. The aircraft was designated A6M2-N.

The first prototype A6M2-N was flown on December 7, 1941, the first day of the Pacific War. Production was ordered under the designation Navy Type 2 Floatplane Fighter Model 11.

The first production A6M2-N was delivered in April of 1942. The A6M2-N first appeared in combat in the Solomons. The A6M2-N was given the Allied code name RUFE under Capt Frank McCoy's system of assigning hillbilly names to Japanese aircraft. A6M2-Ns were initially deployed to Tulagi, but were caught in the raids leading up to the American landings on Guadalcanal. Although they inflicted some serious damage on the B-17s of the 11th Bombardment Group, these A6M2-Ns were soon destroyed.

The A6M2-N was also used in the Aleutian campaign. In spite of the weight and drag of the float, the A6M2-N was actually quite fast and maneuverable, and could even out-maneuver many Allied fighters if they were unwise enough to try and dog-fight with this floatplane. On several occasions, they succeeded in scoring kills against aircraft as formidable as the P-38 Lightning.

As the war in the Pacific progressed, the A6M2-N was encountered just about everywhere. However, by this time the Japanese Navy had been thrown back onto the defensive, and in this mode the A6M2-N was no match for the Allied land-based fighters which opposed it. In spite of its obsolescence, the A6M2-N was still in service at Lake Biwa on the Japanese island of Honshu, being used primarily to train pilots for Kawanishi N1K1 Kyofu floatplane fighters, but occasionally being called up to act as an interceptor in the defense of central Honshu.

A total of 327 A6M2-N floatplane fighters were built by Nakajima at the Koizumi plant between December 1941 and September 1943.

Specification of Nakajima A6M2-N Navy Type 2 Floatplane Fighter Model 11:

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

Performance: Maximum speed 271 mph at 16,405 feet. Cruising speed 184 mph. Climb to 16.685 feet in 6 minutes 43 seconds. Service

ceiling 32,810 feet. Norma range 715 miles, maximum range 1110 miles. Dimensions: Wingspan 39 feet 4 7/16 inches, length 33 feet 1 5/8 inches, height 14 feet 1 5/16 inches, wing area 241.54 square feet. Weights: 4235 pounds empty, 5423 pounds loaded, 6349 pounds maximum. Armament: Two 7.7-mm Type 97 machine guns in upper fuselage decking and two 20-mm Type 99 cannon in the wings. Two 132-pound bombs could be carried on external racks.

A6M2-K two-seat trainer

The A6M2-K was a two-seat training version of the A6M2 Zero Fighter.

The 21st Naval Air Arsenal at Sasebo converted a single A6M2 under a 17-Shi specification by fitting a two-seat cockpit, with student pilot forward and instructor behind. An enlarged canopy was fitted, which for some reason did not fully enclose the student's seat. The fuselage fuel tank was removed, and the two 20-mm wing guns were removed. Small horizontal fins were fitted on the side of the fuselage ahead of the stabilizers for added stability. The main wheel fairings were eliminated. The aircraft was designated A6M2-K.

Following naval evaluation, it was ordered into production as the A6M2-K Zero-Rensen (Zero Fighter Trainer). Starting in November 1943, 236 A6M2-Ks were built by the 21st Naval Air Arsenal, and a further 272 were built from May 1944 at Hitachi's Chiba plant.

The A6M2-K two-seaters were extensively operated in Japan and Formosa as advanced trainers. They were also modified as target tugs by the removal of the tail cone and the installation of a cable container underneath each wing. Many were expended in kamikaze attacks in the last few months of the war.

Specification of A6M2-K:

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

Performance: Maximum speed 296 mph at 13,125 feet. Cruising speed 214 mph. Climb to 19,685 feet in 7 minutes 56 seconds. Service ceiling 33,400 feet. Normal range 860 miles.

Dimensions: Wingspan 39 feet 4 7/16 inches, length 30 feet 0 1/4 inches, height 11 feet 7 3/16 inches, wing area 241.54 square feet. Weights: 4010 pounds empty, 5146 pounds loaded, 5792 pounds maximum. Fuel capacity: 83.6 Imp gall carried internally. Drop tank not carried.

Armament: Two 7.7-mm Type 97 machine guns in upper fuselage decking. Two 132-pound bombs could be carried on underwing racks.

A6M3 "Hap"

In mid-1941, work began on a new version of the Zero Fighter, the A6M3 powered by a 1130 hp Sakae 21. This engine was equipped with a two-speed supercharger instead of a single-speed unit as used on the earlier Sakae 12. The new engine required that the firewall be moved 8 inches further aft, which reduced the fuselage fuel capacity from 21.6 Imp gall to 13.2 Imp gall. The shape of the engine cowling had to be changed in order to incorporate the supercharger air intake in its upper lip.

The first A6M3 flew in June of 1941. Although the aircraft performed satisfactorily, the flight trials of the A6M3 were somewhat disappointing since performance figures fell below the calculated values. In addition, production had to be delayed until sufficient numbers of Sakae 21 engines became available.

The type was placed in production as the Navy Type 0 Carrier Fighter Model 32. Beginning with the fourth aircraft, the ammunition supply for the wing-mounted 20-mm cannon was increased from 60 rpg to 100 rpg. Soon thereafter, in order to simplify production and maintenance, the folding wingtips and the tab balances were removed, reducing the wingspan to 36 feet 1 1/16 inches and wing area to 231.75 square feet. This resulted in a slight increase in the level speed with little adverse effect in the overall maneuverability. Japanese pilots did find that both the maneuverability and climb rate of the new clipped-wing Zero Fighter were slightly poorer than those of the earlier A6M2, but the aircraft was considerably faster in a dive, the ailerons were more effective, and the roll rate was better at high speed.

343 A6M3s were built by Mitsubishi, with an unspecified number also being built by Nakajima at Koizumi.

Following limited service in Japan, the A6M3s were deployed to the New Guinea/Solomons area in the late spring of 1942 in preparation for the invasion of Australia. Initially, the Allies thought that the A6M3 was an entirely new fighter because of its squared-off wingtips, and Capt. Frank McCoy's team at the Directorate of Intelligence of the Allied Air Forces, Southwest Pacific Area, assigned it the code name HAP, after the nickname of General Henry Arnold, the USAAF's Chief of Staff. The General was not amused, and had Capt. McCoy called onto the carpet to explain just what he was up to. Capt McCoy seems to have survived this particular episode, but the code name of the new square-winged fighter was quietly changed to HAMP. When Allied intelligence finally recognized that the aircraft was not a new design but was actually a modified version of the ZEKE, it was renamed ZEKE 32.

Following the American landing at Guadalcanal, the A6M3 were forced to operate from bases 560 nautical miles away from the landing force. During this operation, a large number of A6M3s were lost because they had insufficient range. The Sakae 21 engine of the A6M3 had a higher fuel consumption rate than the Sakae 12, and this, acting in concert with the reduced fuel capacity resulting from the installation of the two-speed supercharger, had an adverse effect on range, which had been one of the strong points of the A6M2. In order to increase the range, a 9.9 Imp gall fuel tank was fitted in each wing outboard of the cannon. The folding wingtips were restored. This new version was still known under the short designation A6M3, but bore the new designation of Navy Type 0 Carrier Fighter Model 22. It could be externally distinguished from earlier A6M3 models by the rounded-off wingtips. The aircraft was known as the Navy Type 0 Carrier Fighter Model 22A when long-barreled 20-mm Type 99 Model 2 Mk 3 cannon were installed. The rounded-wingtip Model 22 became the prime carrier fighter of the A6M3 series, some 560 being built by Mitsubishi.

Specification of A6M3 Navy Type 0 Carrier Fighter Model 32:

One Nakajima NK1F Sakae 21 fourteen cylinder air-cooled radial, rated at 1130 hp for takeoff, 1100 hp at 9350 feet, 980 hp at 19,685 feet.

Performance: Maximum speed 338 mph at 19,685 feet. Cruising speed 230 mph. Initial climb rate 4500 feet per minute. Radius of turn with entry speed at 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 6.02 seconds, with an exit speed from the turn of 189 mph. At slower speed, the radius of turn was 629 feet. Climb to 19,685 feet in 7 minutes 19 seconds. Service ceiling 36,250 feet. Maximum range 1477 miles.

Dimensions: Wingspan 36 feet 1 1/16 inches, length 29 feet 8 11/16 inches, height 11 feet 6 5/32 inches, wing area 231.75 square feet. Weights: 3984 pounds empty, 5609 pounds loaded.

Armament: Two 7.7-mm Type 97 machine guns in the upper fuselage decking and two 20-mm Type 99 cannon in the wings. A 72.6-Imp gall drop tank could be carried underneath the fuselage.

A6M4

By late 1942 and early 1943, the Zero Fighter was beginning to be confronted with newer, more-capable Allied fighters. At high altitude, the A6M2 and A6M3 were hopelessly outclassed by newer Allied fighters such as the P-38 Lightning and the F4U Corsair. In an attempt to correct this deficiency, two A6M2s were modified by Dai-Ichi Kaigun Koku Gijitsusho at Yokosuka to take an experimental turbosupercharged Sakae engine. The short designation A6M4 was assigned to this project.

However, major teething troubles were encounted with the A6M4, and no production order was placed. As a substitute, the A6M5 interim version was introduced pending availability of the A7M Reppu.

A6M5

By early 1943, the war was beginning to go badly for the Japanese, and new, more capable Allied fighters such as the Lockheed P-38 Lightning and the Vought F4U Corsair had begun to appear. The Lockheed P-38 Lightning was introduced into combat in the Aleutian theatre in August of 1942 and in the New Guinea theatre in the autumn of 1942. The P-38 had an excellent high-altitude performance, a high diving speed, and heavy armament. The US Navy introduced the Vought F4U Corsair in combat on February 13, 1943 during a raid on Bougainville. This fighter had high top speed, good diving performances, rugged construction, heavy armament, and good protection for the pilot and fuel tank. With these two American fighters committed to combat in large quantities, the Zero began to lose control of the air.

One of the primary weaknesses of the early Reisen was its insufficient diving speed, with less-maneuverable Allied fighters often being able to engage the Zero successfully in a diving encounter or else being able to escape destruction by diving to safety, the Zero being unable to follow. This forced the Japanese Navy to consider the development of an improved version of the Reisen, since the hoped-for generation of new fighter aircraft had yet to materialize. The A6M5 Model 52 was the result.

In the pursuit of better combat capability (especially a higher diving speed), the 904th Reisen (an A6M3) was converted as a prototype for what was to become the A6M5 series. This project was supervised by engineer Mijiro Takahashi, who had taken over development of the Zero from Jiro Horikoshi so that the latter could concentrate on the J2M Raiden interceptor. The converted aircraft was fitted with a new set of wings with heavier gauge skin and with redesigned, non-folding rounded wingtips. The wingspan was reduced to 36 feet 1 1/16 inches and wing area to 229.3 square feet. The standard A6M3 armament of two 20-mm cannon and two 7.7-mm machine guns was retained, as were the two wing tanks and the Sakae 21 engine. However, new individual exhaust stacks were fitted to the cylinder heads, which added some residual thrust.

The first A6M5 flew in August of 1943. In spite of an increase in all-up weight of 440 pounds, the A6M5 was faster than the A6M3 Model 32, and could reach a maximum level speed of 351 mph at 19,685 feet.

More important, it could now be dived at speeds of up to 410 mph. It was rushed into production as the Navy Type 0 Carrier Fighter Model 52.

The Model 52 began to reach front line units in the autumn of 1943. It was immediately confronted by the new Grumman F6F Hellcat, which was slightly less maneuverable but which was much more strongly built, heavier armed, and better protected.

The A6M5 saw its first major action in June of 1944 with the Allied invasions of the Marianas. On June 19, 1944, a fleet of dive bombers and torpedo bombers escorted by 108 A6M5s attempted to attack Admiral Raymond A. Spruance's Task Force 58. The attacking force was decimated by intercepting F6F Hellcats, and those planes that managed to get through found it almost impossible to penetrate the heavy screen of anti-aircraft fire. The Japanese attack force lost some 300 aircraft that day in what was later to be known as the "Marianas Turkey Shoot". Losses were so devastating that the Japanese navy was never able again to mount any sort of sizable offensive air action.

Despite the fact that the Zero Fighter was by now outclassed by Allied fighters such as the Grumman F6F Hellcat and the Vought F4U Corsair, the A6M5 became numerically the most important Japanese fighter and was the version of the Reisen built in the largest numbers. Since Japanese industry was unable to come up with sufficient numbers of higher-performing replacements, the manufacture of the A6M5 series continued until the end of the Pacific War. Mitsubishi built 747 Model 52s. Nakajama also built the the Model 52 during 1943-44 --- the exact number is not known --- and Hitachi was also scheduled to build the A6M5, but production snags prevented that company from completing even a single example before the war ended in August of 1945.

Among the field modifications carried out to A6M5s was the addition of a 20-mm cannon mounted to fire obliquely upward at an angle of 30 degrees from a position behind the pilot's cockpit. These fighters were intended as B-29 Superfortress interceptors.

Some A6M5s were converted to dive bombers by replacing the centerline drop tank by a rack for a single 550-pound bomb. Unfortunately, the rack was mechanically unreliable, and frequently failed to release its bomb when commanded to do so by the pilot. Consequently, many Zero dive bombers were forced to fly back to their bases with their bombs still attached, and many were forced to ditch at sea and were lost.

This was of course not a problem for those A6M5s that were used for kamikaze attacks. Modified Zeros assigned to Air Group 201 based in the Philippines carried out the first suicide missions against American naval units. The first such attack was carried out on October 25, 1944, led by Lt Yukio Seki. These suicide aircraft were at first primarily modified obsolete A6M2s, but modified A6M5s were later used as well. These attacks were an outstanding success, and other Kamikaze units were formed, primarily equipped with Zero fighters modified to carry 500-lb bombs underneath their fuselages. In ten months of use, suicide aircraft accounted for nearly half of all US warships damaged. Nevertheless, the desperate Kamikaze attacks were not able to stop the relentless American advance across the Pacific to Japan.

Specification of A6M5 Navy Type 0 Carrier Fighter Model 52:

One Mitsubishi NK1F Sakae 21 fourteen cylinder air-cooled radial, rated at 1130 hp for takeoff, 1100 hp at 9350 feet, 980 hp at 19,685 feet.

Performance: Maximum speed 351 mph at 19,685 feet. Cruising speed 230 mph. Climb to 19.685 feet in 7 minutes 1 second. Service ceiling 38,520 feet. Maximum range 1171 miles at a cruising speed of 230 mph.

Dimensions: Wingspan 36 feet 1 1/16 inches, length 29 feet 11 3/32 inches, height 11 feet 6 5/32 inches, wing area 229.27 square feet. Weights: 4136 pounds empty, 6025 pounds loaded.

Armament: Two 7.7-mm Type 97 machine guns in the upper fuselage decking and two 20-mm Type 99 cannon in the wings. Two 132-lb bombs could be carried on underwing racks.

A6M5a

In response to a need for heavier firepower and even better diving performance, the A6M5a version of the Zero Fighter was produced. The A6M5a Model 52A appeared in late 1943 and began rolling off the production lines at Mitsubishi and Nakajima in March of 1944. It had still heavier gauge wing skin which enable a further increase in diving speed to 460 mph, bringing it almost up to Western standards. This was to be the highest diving speed attained by any Reisen variant. Armament was improved by replacing the drum fed Type 99 Model 2 Mk3 cannon with 100 rpg with belt-fed 20-mm Type 99 Model 2 Mk4 cannon with 125 rpg.

Delivery of the Model 52A began in March of 1944. Mitsubishi built 391 Model 52As. Nakajima also produced the type, but I don't know the actual number built.

Specification of A6M5a Navy Type 0 Carrier Fighter Model 52a:

One Mitsubishi NK1F Sakae 21 fourteen cylinder air-cooled radial, rated at 1130 hp for takeoff, 1100 hp at 9350 feet, 980 hp at 19,685 feet.

Performance: Maximum speed 348 mph at 19,685 feet. Cruising speed 230 mph. Climb to 19.685 feet in 7 minutes 1 second. Service ceiling 38,520 feet. Maximum range 1195 miles at a cruising speed of 230 mph. Dimensions: Wingspan 36 feet 1 1/16 inches, length 29 feet 11 3/32 inches, height 11 feet 6 5/32 inches, wing area 229.27 square feet. Weights: 4167 pounds empty, 6047 pounds loaded.

Armament: Two 7.7-mm Type 97 machine guns in the upper fuselage decking and two 20-mm Type 99 cannon in the wings. Two 132-lb bombs could be carried on underwing racks.

A6M5b

Since the J2M Raiden interceptor and the A7M Reppu carrier-based fighter programs had run into delays, the Japanese Navy had no alternative but to continue with progressive developments of the Reisen, which was by now thoroughly outclassed by more modern Allied warplanes.

One of the weaknesses of the Zero Fighter was its lack of any protection for its fuel tanks, which made it prone to catching fire even when only superficially damaged in combat. In addition, the excellent maneuverability and good climbing performance of the Zero Fighter had been achieved to a certain extent at the expense of the omission of armor protection for the pilot, which became more and more of a serious problem as the war continued.

The A6M5b Model 52B originated as a private venture jointly developed by Mitsubishi and Dai-Ichi Kaigun Kokusho to carry additional armament and to provide some fire protection for the fuel tanks and some armor protection for the pilot. Armored glass was provided for the windshield, which consisted of two layers of plastic mounted between glass outer-sections. The total armored windshield was two inches thick. The fuel tanks were provided with automatic CO2-type fire extinguishers. One of the fuselage-mounted 7.7-mm Type 97 machine guns was replaced by a 13.2-mm Type 3 machine gun.

Production of the Model 52B began at Mitsubishi's 3rd airframe plant in April of 1944, and 470 fighters of this type were built. This version was perhaps the best version of the Reisen to see active duty. The Model 52B was available in time for the US Navy's amphibious operations to capture the Marianas in preparation for the B-29 offensive against Japan. However, the Model 52B was no match for the F6F Hellcat, and dozens were lost on June 19, 1944 during what came to be known as the "Marianas Turkey Shoot".

Mitsubishi built 470 Model 52Bs.

Specification of A6M5b Navy Type 0 Carrier Fighter Model 52B:

One Mitsubishi NK1F Sakae 21 fourteen cylinder air-cooled radial, rated at 1130 hp for takeoff, 1100 hp at 9350 feet, 980 hp at 19,685 feet.

Dimensions: Wingspan 36 feet 1 1/16 inches, length 29 feet 11 3/32 inches, height 11 feet 6 5/32 inches, wing area 229.27 square feet. Armament: One 7.7-mm Type 97 machine gun and one 13.2-mm Type 3 machine gun in the upper fuselage decking and two 20-mm Type 99 cannon in the wings. Two 132-lb bombs could be carried on underwing racks.

A6M5c

Despite the obsolescence of the basic design, development of the Reisen continued into the summer of 1944. About a month after the Marianas disaster, on July 23, 1944, the Japanese Navy issued another Zero Fighter improvement order. This time the Navy demanded Zero Fighters with even more armor, armament, fuel tankage, and bomb delivery capability. The A6M5c was the result.

Design engineer Eitaro Sano headed up the Mitsubishi team. The A6M5c Model 52C differed from earlier Zero Fighters in having two additional 13.2-mm machine guns installed in the wings outboard of the cannon. The fuselage-mounted 13.2-mm machine gun was retained, but the smaller-calibre 7.7-mm fuselage-mounted gun was deleted. An armor plate was mounted behind the pilot's seat to provide some protection against attacks from the rear, and a 30.8 Imp gall self-sealing fuel tank was installed behind the cockpit. Wing racks were provided for unguided air-to-air rockets.

The Zero Fighter was now beginning to suffer from the disease which had affected lots of other fighters --- a steady increase in the weight caused by the addition of more fuel, armament, and armor without a corresponding increase in engine power. Sano now felt that the Sakae radial would be insufficiently powerful, and recommended that the Sakae engine be replaced by the more powerful Mitsubishi Kinsei 62 engine. However, the Navy refused to allow this and ordered Mitsubishi to retain the Sakae radial. Nevertheless, they did allow Mitsubishi to use the improved Sakae 31 with water-methanol injection in the A6M5c. However, this engine was not available in time for installation in production A6M5c fighters, and so they had to rely on the Sakae 21 engine.

The first A6M5c was obtained by modifying an A6M5 airframe, and took off on its flrst flight in September of 1944. During flight testing, it was found necessary to increase the thickness of the wing covering in the region of the gun bays in order to achieve the desired diving performance. The design was put into production as the Navy Type 0 Carrier Fighter Model 52C.

The self-sealing tanks planed for the Model 52C were not actually fitted to production aircraft because of the lack of experience of ground crews in dealing with this type of fuel tank. As expected, the increased weight proved to be too much for the power available from the Sakae 21, and the performance of the A6M5c was disappointing. Consequently, production of the Model 52C was terminated after the delivery of only 93 machines.

Specification of A6M5c Navy Type 0 Carrier Fighter Model 52C:

One Mitsubishi NK1F Sakae 21 fourteen cylinder air-cooled radial, rated at 1130 hp for takeoff, 1100 hp at 9350 feet, 980 hp at 19,685 feet.

Performance: Maximum speed 348 mph at 19,685 feet. Cruising speed 230 mph. Climb to 16,405 feet in 5 minutes 50 seconds. Service ceiling 36,255 feet. Maximum range 1314 miles at a cruising speed of 230 mph.

Dimensions: Wingspan 36 feet 1 1/16 inches, length 29 feet 11 3/32 inches, height 11 feet 6 5/32 inches, wing area 229.27 square feet. Weights: 4751 pounds empty, 6945 pounds loaded.

Armament: one 13.2-mm Type 3 machine gun in the upper fuselage decking, two wing-mounted 13.2-mm Type 3 machine guns and two wing-mounted 20-mm Type 99 cannon.

A6M5-K two-seat trainer

The A6M5-K Model 22 was a two-seat tandem advanced fighter trainer version of the basic A6M5. It was similar to the A6M2-K, a two-seat adaptation of the earlier A6M2.

The Sasebo Naval Air Arsenal undertook the project design, and work on the prototypes began in August of 1944. Production was to be carried out by Hitachi, but only a small experimental batch of seven A6M5-Ks were built in March of 1945. By this time, the deteriorating course of the Pacific War had placed emphasis on combat aircraft, and no more two-seat A6M5-Ks were built.

A6M6c

The A6M6c was the next variant of the Zero Fighter. The A6M6c was powered by the water-methanol boosted Sakae 31 engine, which finally became available in November of 1944. The Sakae 31 had the same rated horsepower as the Sakae 21, but had a water-methanol injection system for short bursts of speed. The aircraft was otherwise similar to the A6M5c, but it did have self-sealing wing tanks substituted for the previously-unprotected tanks.

One prototype of the A6M6c was built by Mitsubishi in late 1944, but the production of the A6M6c Model 53C was assigned to Nakajima at the Koizuma plant. A small quantity of A6M6c fighters were turned out by Nakajima, the exact number being unknown.

Although a maximum speed of 346 mph could be achieved with the Sakae 31 engine, the actual performance was usually below this because of poor quality control in the manufacture of the engine and airframe. In addition, the Sakae 31 engine did not produced the expected boosted power and the injection system was troublesome and difficult to maintain.

Specification of A6M6c Navy Type 0 Carrier Fighter Model 52C:

One Mitsubishi NK1F Sakae 31 fourteen cylinder air-cooled radial, rated at 1130 hp for takeoff, 1100 hp at 9350 feet, 980 hp at 19,685 feet.

Performance: Maximum speed 337 mph at 21,000 feet. Cruising speed 230 mph. Climb to 26,250 feet in 9 minutes 53 seconds. Service ceiling 33,300 feet. Maximum range 956 miles at a cruising speed of 230 mph.

Dimensions: Wingspan 36 feet 1 1/16 inches, length 29 feet 11 3/32 inches, height 11 feet 6 5/32 inches, wing area 229.27 square feet. Weights: 4519 pounds empty, 6614 pounds loaded.

Armament: One 13.2-mm Type 3 machine gun in the upper fuselage decking, two wing-mounted 13.2-mm Type 3 machine guns and two wing-mounted 20-mm Type 99 cannon. Eight 22-lb rockets or two 132-lb rockets could be carried underneath the wing.

A6M7 dive bomber

By late 1944, most of the larger Japanese aircraft carriers had been sunk, and the Japanese Navy instructed Mitsubishi to begin development of a version of the Reisen capable of being used as a dive bomber operating from smaller aircraft carriers. The A6M7 was designed to meet this requirement.

The A6M7 differed from the A6M6c in having the under-fuselage drop tank installation replaced by a special bomb rack capable of carrying a single 551 pound or 1100 pound bomb. A strengthened and reinforced tailplane was provided to accommodate the stresses of dive bombing. In place of the centerline drop tank, provisions were made for two 77 Imp gall drop tanks to be attached underneath the wings outboard of the 13.2-mm machine guns.

Production of the A6M7 began as the Model 63 in May of 1945. It was hastily produced both by Mitsubishi and Nakajima and issued to Navy dive-bomber units. The exact numbers built by either company is not known. The bomb-release mechanism proved to be more reliable than the makeshift racks fitted in the field to earlier Zero Fighters that often failed to release their bombs. This problem did not of course affect the Zeros that were expended in Kamikaze attacks. Some of the A6M7s were also expended in this fashion in the closing months of the Pacific War.

Specification of A6M7 Navy Type 0 Carrier Fighter Model 63:

One Mitsubishi NK1F Sakae 31 fourteen cylinder air-cooled radial, rated at 1130 hp for takeoff, 1100 hp at 9350 feet, 980 hp at 19,685 feet.

Dimensions: Wingspan 36 feet 1 1/16 inches, length 29 feet 11 3/32 inches, height 11 feet 6 5/32 inches, wing area 229.27 square feet. Weights: 6945 pounds loaded.

Armament: One 13.2-mm Type 3 machine gun in the upper fuselage decking, two wing-mounted 13.2-mm Type 3 machine guns and two wing-mounted 20-mm Type 99 cannon. One 551-lb or 1102-lb bomb could be carried underneath the fuselage centerline. Two 77-Imp gall droptanks could be carried underneath the wings.

A6M8

The A6M8 was the last production version of the Reisen. Bomb damage to the Nakajima engine plants (as well as Nakajima's decision to decrease Sakae production in preparation for the production of the 18-cylinder Homare radial) had resulted in a shortage of the Sakae radial engines which had previously powered the Zero Fighter. Consequently, the Navy finally accepted Mitsubishi's proposal to use their more powerful MK8K Kinsei 62 (Ha-33/62) fourteen-cylinder air-cooled radial engine.

Manufacture of the Kinsei-powered A6M8 prototypes was finally approved in November 1944. The forward fuselage was completely redesigned to accommodate the 1560 hp Mitsubishi MK8P Kinsei 62, which had a larger diameter than the Sakae, requiring that the fuselage-mounted gun be removed. At the same time, the fuel tank fire-extinguishing system was improved, and additional fuel tankage was added. The fuselage centerline could carry a single 1100-lb bomb, and a pair of 77-Imp gall drop tanks could be carried underneath the wings.

The first A6M8 was completed in April of 1945. Flight tests turned up a number of faults in the fuel and oil systems, plus a tendency to overheat, and the machine had to be returned to the factory for these to be corrected. By enlarging the oil tank, revising the pipe lines, and by fitting engine cooling baffles, these snags were eliminated. At high altitudes, the tendency for the fuel pressure to drop was overcome by altering the fuel regulating valve.

After completion of service trials at Aomori, on May 25, 1945 the A6M8 was approved for manufacture as the Navy Type 0 Carrier Fighter Model 64. A second prototype was accepted in June, and both were turned over to the Yokosuka Experimental Air Corps Proving Division throughout July.

Production of the A6M8 was assigned to dispersed Mitsubishi and Nakajima factories, with as many as 6300 machines being ordered. However, owing to the chaotic conditions prevailing in Japanese industry in the closing months of the war, none were actually delivered.

Specification of A6M8 Navy Type 0 Carrier Fighter Model 64:

One Mitsubishi MK8P Kinsei 62 fourteen cylinder air-cooled radial, rated at 1560 hp for takeoff, 1340 hp at 6890 feet, 1180 hp at 19,030 feet.

Performance: Maximum speed 356 mph at 19,685 feet. Climb to 16.685 feet in 6 minutes 50 seconds. Service ceiling 37,075 feet. Dimensions: Wingspan 36 feet 1 1/16 inches, length 30 feet 3 21/32 inches, height 11 feet 11 7/32 inches, wing area 229.27 square feet. Weights: 4740 pounds empty, 6945 pounds loaded.

Armament: Two 13.2-mm Type 3 machine guns and two 20-mm Type 99 cannon in the wings. A single 1100-lb bomb could be carried underneath the fuselage centerline. An additional two 132-lb bombs could be carried underneath the wings.

Sources:

· Japanese Aircraft of the Pacific War, Rene J. Francillon, Naval Institute Press, 1979.

· Famous Fighters of the Second World War, William Green, Doubleday, 1967.

· Zero Fighter, Martin Caidin, Ballantine, 1970.

· War Planes of the Second World War, Fighters, Volume 3, William Green, Doubleday 1964.

· The Mitsubishi A6M2 Zero-Sen, Rene J. Francillon, Aircraft in Profile, Doubleday, 1969.

· Mitsubishi A6M5 to A6M8 Zero-Sen, M.C. Richards and Donald S. Smith, Aircraft in Profile, Doubleday, 1974.

Joe Baugher
jfb@ihgp.ih.att.com