The Mitsubishi A6M Zero

v1.3.7 / 01 feb 17 / greg goebel

* The Japanese began World War II with a number of excellent weapons that gave them a decisive advantage during their first half-year's rampage across the Pacific. One of them was a superbly maneuverable, well-armed naval fighter designated the "A6M", better known simply as the "Zero". In the hands of well-trained Japanese pilots, the Zero gave the Imperial Japan Navy air superiority in its wave of conquests. In reality, although the Zero had a number of advantages, it had significant limitations as well, and as Allied pilots took its measure, it slowly declined from a master of the skies to, literally, a suicide craft. This document describes the rise and fall of the Zero fighter.

Mitsubishi A6M Zero

[1] A5M

[1] A5M

* In 1932, the Imperial Japanese Navy (IJN) issued a requirement for a new naval carrier fighter. In response a Mitsubishi design team under Horikoshi Jirou developed the "1MF10" fighter, which had a strong resemblance to the American Boeing P-26 "Peashooter", being a low-wing monoplane, with a metal fuselage and fabric-covered wings; an open cockpit; an air-cooled radial engine, driving a two-bladed fixed wooden propeller; fixed landing gear; twin 7.7-millimeter (0.303-caliber) machine guns in the upper lip of the engine cowling; and a telescopic tube gunsight.

The first of two prototypes performed its initial flight in March 1933. The second prototype followed shortly after and differed from the first by replacing the strut-braced main landing gear with main gear in spats. The 1MF10 was an unlucky aircraft. It failed to meet IJN performance requirements, and both prototypes were lost in crashes. It did, however, give Horikoshi and Mitsubishi a basis for further work.

In 1934, the IJN issued another request for a carrier fighter, and Mitsubishi and Horikoshi came up with a new design, the "Ka-14", with the same overall configuration as the 1MF10 but cleaner, featuring all-metal construction, an inverted gull wing, and a Nakajima Kotobuki 5 nine-cylinder radial providing 410 kW (550 HP). The initial prototype performed its first flight on 4 February 1935. The prototype exceeded its speed requirements, but it had a number of handling problems.

As a result, the inverted gull wing was replaced in the second prototype by a flat wing with a slight outboard dihedral. The second prototype also featured an uprated Kotobuki 3 radial with 475 kW (640 HP). Four more prototypes were built that were similar to the second prototype, differing in small details and being used to evaluate a variety of engine fits. Following successful trials, the IJN approved production of the type as the "A5M1" or "Type 96 Carrier Fighter Model 1", powered by a Kotobuki-2-KAI-1 engine with 430 kW (580 HP).

The Imperial Japanese Army (IJA) also found the Ka-14 interesting, ordering a "Ki-18" prototype similar to the second Ka-14 prototype. The Ka-18 flew in the summer of 1935 and led to two prototypes of an improved "Ki-33" that first flew in the spring of 1936. However, the IJA did not order the Ki-33 into production.

* The first A5M1s were delivered to the IJN in early 1937, with the type going into combat service over China, where it quickly obtained air superiority over Chinese forces. It was followed by the"A5M2a", with an uprated Kotobuki 2-KAI-3A engine, and then the "A5M2b" with a Kotobuki 3 radial engine, improved cowling design, a three-bladed fixed prop, and a sliding canopy. The sliding canopy would prove unsatisfactory and was deleted in late production.

Two experimental "A5M3a" prototypes were built, fitted with an imported water-cooled Hispano-Suiza inline vee-12 engine, with a Hispano-Suiza 20-millimeter cannon mounted between the cylinders. Use of a water-cooled engine was a extraordinary departure for Mitsubishi, and this variant would not go into production.

Mistubishi A5M4

The final and definitive "A5M4" variant was basically much like the late-production A5M2b, but with a further uprated Kotobuki 41 radial and a centerline external tank with a capacity of 160 liters (42 US gallons). Initial deliveries of the A5M4 were in early 1938.

   _____________________   _________________   _______________________
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                11 meters           36 feet 1 inch
   wing area               17.8 sq_meters      191.6 sq_feet   
   length                  7.56 meters         24 feet 10 inches
   height                  3.27 meters         10 feet 9 inches

   empty weight            1,216 kilograms     2,681 pounds
   loaded weight           1,671 kilograms     3,684 pounds

   max speed at altitude   435 KPH             270 MPH / 235 KT
   service ceiling         9,800 meters        32,150 feet
   range                   1,200 kilometers    746 MI / 648 NMI
   _____________________   _________________   _______________________

The last A5M4 fighters were rolled out in early 1940, but a little over a hundred tandem seat trainer versions with the designation "A5M4-K" were built into 1943. Almost 1,100 A5Ms of all versions were built. The tandem-seat trainers and such A5M single-seaters as survived spent most of the Pacific War serving in the advanced fighter trainer role, with some used as "Kamikaze (Wind Of The Gods)" suicide-attack aircraft in defense of the Japanese home islands late in the war.



* Although the A5M was a first-class fighter when it was introduced, aircraft design was advancing very rapidly at the time, and in 1937, even as Mitsubishi was ramping up production of the A5M, the IJN was looking for a successor with the same high agility, but with improved speed, range, and firepower.

On 19 May 1937, the IJN issued a request for the new fighter, dictating performance specifications; armament of two 7.7-millimeter machine guns and twin 20-millimeter cannon, plus two 60 kilogram (132 pound) bombs; and state-of-the-art radio gear. The performance specifications were raised in October, in light of experience obtained in fighting in China that year. The specifications were so aggressive that many thought that Japanese aircraft manufacturers could not meet them.

Both Nakajima and Mitsubishi entered the competition, but Nakajima decided to drop out, feeling the specifications really were impossible to meet. Mitsubishi assigned Jirou Horikoshi the task of designing the new fighter. The result was the "A6M1", or "Naval Fighter, Mitsubishi Design Number Six, Variant 1". It first flew on 1 April 1939, with test pilot Shima Katsuzo at the controls.

The initial prototype was fitted with the Mitsubishi Zuisei 13 engine, with 580 kW (780 HP). Top speed was 490 KPH (305 MPH), which was under specification, but the aircraft was otherwise satisfactory. A second A6M1 was flown in October 1939, though it was lost in March 1940 when it exploded in mid-air, killing the test pilot. The cause of the accident was never determined. However, a third prototype had already been flown in January 1940, with the designation "A6M2". This aircraft was fitted with the more powerful Nakajima NK1C Sakae 12 radial, with 690 kW (925 HP). The new engine gave the fighter a top speed of 535 KPH (332 MPH), which exceeded specification.

Mitsubishi A6M1/A6M2 Zero

Service trials were conducted through the first half of 1940, leading to combat trials in China and initial production. In service, the A6M2 was more formally designated the "Type 0 Carrier Fighter (Rei Shiki Kanjo Sentoku) Model 11". The aircraft became informally known as the "Zero Sentoku (Fighter)" or simply "Zero-sen". Since the Japanese use both the imported word "zero" and the more traditional native word "rei" for the number "0", this is also sometimes rendered as "Rei-sen" -- though apparently that wasn't normal usage.

* The Zero was a low-wing design, constructed of a lightweight aluminum alloy named "Extra-Super Duraluminum (ESD)", with the exception of fabric-covered rudder and elevators. The aircraft's lightweight construction helped it achieve the performance goals specified by the IJN. However, the severe limits on weight ensured that the new fighter also lacked armor and self-sealing fuel tanks.

Although a two-blade propeller was initially fitted to the first A6M1 prototype, it led to vibration problems and was replaced by a three-blade variable-pitch Hamilton Standard propeller, built under license by Sumitomo. The aircraft had taildragger landing gear, with main landing gear hinged in the wings and retracting towards the fuselage, giving the Zero a comfortably wide stance on the ground. The tailwheel retracted into a nock under the tail, and a "stinger" type arresting hook was fitted just forward of the tailwheel.

The sliding canopy gave excellent all-round vision, though it featured a "greenhouse" style bracing structure that imposed some visual obstruction. Along with a radio for communications, the Zero carried a radio compass for long range ocean navigation, with the radio direction finding antenna fitted in the cockpit behind the pilot's headrest.

The two Type 97 7.7-millimeter machine guns, a license-built British Vickers design, were fitted in the cowling and fired through the propeller using synchronizing gear. One Type 99 Model 1 20-millimeter cannon, an Oerlikon cannon built under license, was fitted in each wing, for a total of four guns. That was heavy armament for a fighter of that era. An external fuel tank could be fitted under the aircraft's centerline, while one 60-kilogram (132-pound) bomb could be carried under each wing. Some Zero variants were said to have racks for a total of ten 32-kilogram (70.5-pound) bombs, though it is unclear if this was a standard feature in all types of the Zero.



* Another A6M2 prototype was completed, followed by 15 pre-production and 48 production aircraft. The pre-production aircraft were rushed into combat in China in July 1940. The Zero flew its first combat mission on 19 August 1940, escorting a bomb raid on Chungking, but encountered no aerial opposition. The first air combat with Chinese fighters was on 13 September, when Zeroes shot down a force of 27 Soviet-built Polikarpov I-15 biplanes and I-16 monoplanes, which were very maneuverable themselves but not as fast. In its first year of combat, the Zero was credited with destroying 44 Chinese aircraft in the air against the loss of only two Zeroes, both of which were lost to anti-aircraft fire.

In the meantime, Mitsubishi was improving the breed. The second variant of the A6M2 was the "Model 21", which featured manually folding wingtips. This odd feature was added to improve the clearance of the fighter on aircraft carrier elevators. 740 Model 21s were built. Other small changes were made during A6M2 production, such as reinforcement of the wing spar and a few minor aerodynamic tweaks.

* The Model 21 was followed by a major new variant, the "A6M3", which flew for the first time in June 1941. It featured a new engine, the Nakajima NK1F Sakae 21, with a two-speed instead of a single-speed supercharger and 845 kW (1,130 HP); a wider propeller; ammunition supply for the 20-millimeter cannon increased from 60 to 100 rounds per gun (RPG); and clipped wings with no folding wingtips, reducing the wingspan by a meter (3 feet 4 inches). The wingtips were removed to improve manufacturability and maintainability. Early A6M3 production had featured the folding wingtips, but pilots suggested that they could do without them, and so they were deleted.

Aside from the clipped wings, the A6M3 was difficult to distinguish from the A6M2, the most visible difference being that the A6M2 had the supercharger air intake in the lower lip of the cowling, while in the A6M3 the intake was moved to the upper lip. The initial A6M3 variant was designated the "Model 32", and 343 were built.

Integral wing tanks were fitted in the "Model 22". The Sakae 21 engine used in the A6M3 was larger and thirstier than the Sakae 12 used in the A6M2, and led to reduced fuel tankage and range. This resulted in losses of planes and pilots during the battle for Guadalcanal, when aircraft simply ran out of fuel during the long flight down and back up the Solomons chain. The wing tanks gave the A6M3 Model 22 the longest range of all Zero variants. The folding wingtips were restored to reduce wing loading, which had been increasing due to "weight creep" as improvements were added to the Zero.

At least three A6M3 Model 22s were fitted with 30-millimeter cannon in place of the 20-millimeter guns and tested under combat conditions, but nothing came of the exercise. A final variant of the A6M3, the "Model 22a", featured Type 99 Model 2 20-millimeter cannon with longer barrels, higher muzzle velocity, and greater rate of fire. A total of 560 Model 22s and Model 22a's was built by Mitsubishi to summer 1943, and a number were built by Nakajima as well.

* When the Pacific War broke out, there were 328 Zeroes in operational service. The IJN felt with good reason that they had a superior fighter aircraft, and in fact some sources claim that the Japanese would have been much more reluctant to go to war if they hadn't had the Zero. Many IJN pilots thought their Zeroes were invincible, and in fact Japanese intelligence judged one Zero, by no means unreasonably, to be worth two to five contemporary enemy fighters. Cooler heads realized that new fighter designs then being designed and fielded by the enemy would reduce the fighter's margin of superiority in due time; they also realized that, over the longer term, Japan's industrial capability was no match for the USA's.

As the Japanese struck at Pearl Harbor and then swept downward to Southeast Asia, over the Philippines, into the South Pacific, and across the Central Pacific, the Zero proved a complete shock to the Allies, completely overwhelming all resistance in the air. Japanese distrust of all "gaijin", or "foreign people", had ensured that the Zero had remained mostly secret. Although General Claire Chennault, who had been working with the Chinese Nationalists to fight the Japanese, had sent reports to the US on the Zero in 1940, they had been filed and forgotten.

Even the Japanese were (pleasantly) surprised at the Allies' obvious ignorance of the Zero's capabilities. Allied pilots could not cope with the Zero's speed, maneuverability, and firepower. It also had remarkable range for a carrier fighter, with an endurance of up to twelve hours when fitted with a centerline external tank. For the first six months of the Pacific War, the Zero was lord of the air.

Skilled Japanese Navy pilots racked up impressive scores in the Zero. Petty Officer Sakai Saburou ultimately claimed 64 Allied aircraft, while Warrant Officer Nishizawa Hiroyoshi, known as "the Devil", claimed 87. Sakai survived the war, but Nishizawa was killed in action over the Philippines when the Japanese Army bomber he was riding on as a passenger was shot down by US Navy Grumman Hellcat fighters.



* The Zero became the most prominent Japanese fighter, so much so that in the popular American press any radial-engine fighter with red "meatballs" on its wings was often called a "Zero". The Allies were thoroughly intimidated by the Zero. However, although the Grumman F4F Wildcat fighter was inferior to the Zero in maneuverability and in almost all aspects of performance, the ruggedly built Grumman could easily take ten times more punishment than the lightly-built Zero, and could also escape a Zero by going into a dive. After suffering through a nasty learning curve, US Navy and Marine Wildcat pilots learned tactics to allow them to more or less hold their own against the Zero.

Allied pilots were particularly helped when a Zero fighter fell into American hands. On 4 June 1942, Japanese aircraft attacked the American military base at Dutch Harbor in the Aleutians. One Zero fighter was hit during the raid, severing its oil line. The pilot of the damaged Zero, 19-year-old Flight Petty Officer Koga Tadayoshi, knew he couldn't make it back to his carrier, the RYUUJOU, and decided to land his aircraft on the island of Akutan, 40 kilometers (25 miles) away.

Akutan had been designated for emergency landings, with a Japanese submarine standing off the island to assist pilots who were forced down. Koga attempted to land on what he thought was a grassy meadow while two of his wingmates watched on. The grassy meadow turned out to be a marsh, and when Koga touched down, the Zero's main gear dug into the mud and the aircraft flipped over on its back. Koga's two wingmates had orders to prevent a Zero from being captured, but as they were not certain Koga was dead, they were reluctant to shoot up the overturned Zero and destroy it. Koga did not emerge, and his wingmates finally had to depart in order to make it back to the RYUUJOU.

In fact, Koga was dead. His neck had been broken when the aircraft flipped over. On 10 July 1942, a US Navy Consolidated PBY Catalina flying boat on patrol spotted the Zero, then setting down on the waves so the crew could go ashore and examine the downed fighter. They excitedly reported their find to their superiors and an expedition was sent to recover the downed aircraft. Navy workers laboriously dragged the Zero onto a skid and pulled out of the bog with a tractor, put the aircraft on a barge, and brought it to Dutch Harbor. Koga's body was buried on Akutan, to be repatriated back to Japan after the war.

Koga's Zero

At Dutch Harbor, the Zero -- which was still on its back -- was righted, cleaned up, and put in a crate for shipment to San Diego. The Zero's wings could not be detached in any convenient way, and so the crate was very big and clumsy. The inability to remove the wings was a nuisance for the Japanese as well, but adding such a feature would have increased the aircraft's weight.

After arrival in San Diego, the Zero, which turned out to be an A6M2 Model 21 with a manufacturing date stamp of 19 February 1942, was repaired. One problem was that the propeller was damaged beyond repair, but that was easy to fix, since the Sumitomo design was a straight copy of a readily available Hamilton Standard propeller. Flight evaluations of the captured aircraft began in late September 1942, and demonstrated the performance capabilities and limitations of the type.

While the Zero was supremely maneuverable at low speeds, its controls became heavy at high speeds, and it rolled left much more easily than it rolled right. Also, due to its float-type carburetor it tended to stall under negative gees, as would be encountered if the Zero was climbing and then had to bob back downward while remaining upright. An American fighter could escape the Zero by bobbing up, diving while the Zero's engine stalled, and then rolling to the right. Japanese writer Okumiya Masatake, author of the classic book ZERO, claimed that the loss of Koga's Zero was no less serious than the Japanese defeat at Midway. That was clearly an exaggeration; the Allies would have got its measure sooner or later, but it was still lucky they managed to capture one in the first year of the war in the Pacific.

* With the introduction of more advanced fighters like the Lockheed P-38 Lightning, the Grumman F6F Hellcat, and the Vought F4U Corsair, which were not only more powerful and robust aircraft, but were built in numbers the Japanese could not hope to match, the Zero lost the advantage. The Japanese fighter still held an edge in maneuverability, but American pilots generally knew better than to get suckered into a turning contest and made the most of their superior speed, ruggedness, and firepower.

The Zero became a second-rate fighter. To make matters much worse, combat attrition was steadily eliminating the Japanese Navy's best pilots, and the Japanese could not provide adequate training to the needed volume of replacements. Japanese pilots, once experienced and confident, were becoming second-rate as well, and increasingly outmatched by Allied pilots who had learned the trade the hard way, as well as increasingly effective anti-aircraft fire.

death of a Zero

The Japanese aircraft industry attempted to design and produce improved fighters to replace the Zero, but Japan simply did not have the engineering and manufacturing capability to keep pace. The Japanese had no choice but to keep on building Zero fighters. Attempts to improve the type's performance didn't work out.

Two "A6M4s" were converted from A6M2s by fitting them with a turbocharged Sakae engine, but the new engine could not be made to work reliably and the A6M4 was abandoned. In fact, some air historians have wondered if there ever was an A6M4 in the first place. The Japanese tend to avoid use of the number 4, since in Japanese it can be spoken as "shi", which also means "death", making the number unlucky. Skipping a designation such as A6M4 would have a definite basis, but postwar examination of records showed that the variant did actually exist.

* A more modest update, the "A6M5" or "Model 52", began life as an A6M3 with new wings to permit faster dives, featuring a thicker skin and rounded, non-folding wingtips, as well as a new exhaust system that provided a slight amount of additional speed from exhaust thrust. The A6M5, or "Type 0 Carrier Fighter Model 52", went into production in the fall of 1943, and demonstrated a noticeable improvement in performance.

   _____________________   _________________   _______________________
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                11 meters           36 feet 1 inch
   wing area               21.3 sq_meters      229.27 sq_feet   
   length                  9.12 meters         29 feet 11 inches
   height                  3.51 meters         11 feet 6 inches

   empty weight            1,875 kilograms     4,135 pounds
   max loaded weight       2,733 kilograms     6,025 pounds

   maximum speed           565 KPH             350 MPH / 305 KT
   service ceiling         11,050 meters       36,250 feet
   range                   1,920 kilometers    1,195 MI / 1,040 NMI
   _____________________   _________________   _______________________

Two sub-variants followed. The "A6M5a", or "Model 52a", had even thicker wing skinning, and cannon with belt feed instead of drum feed in the wings. The belt feed allowed the ammunition for the cannons to be increased from 100 to 125 RPG.

The "A6M5b", or "Model 52b", incorporated an armor glass windscreen and a fuel-tank fire extinguisher to reduce the aircraft's inclination to immediately burst into flames when hit. The A6M5b also replaced one of the 7.7-millimeter guns in the cowling with a 13.2-millimeter Type 3 machine gun, a license-built Browning.

The "A6M5C" or "Model 52c" added armor plate and larger fuel tanks with self-sealing, and featured one 13.2-millimeter gun in the cowling, plus a 20-millimeter and 13.2-millimeter gun in each wing, for a total of five guns. The A6M5c first flew in September 1944. The A6M5 series machines were the most heavily produced Zero variants, with at least 5,000 built.

The A6M5c was just an interim fit until the more powerful Sakae 31A engine, which featured water-methanol power boost, was ready for service. The first Zero with such an uprated engine, the "A6M6c" or "Model 53c", performed its initial flight in November 1944. It was similar to the A6M5c except for the new engine and self-sealing wing tanks. Production was performed by Nakajima. The Sakae 31A engine provided noticeably improved performance, when it worked properly, but under the pressures of war Japanese manufacturing quality was in steep decline.

kamikaze grazes USS MISSOURI

* By this time the Zero's most important mission was Kamikaze suicide attack, with the aircraft fitted with a 250-kilogram (550-pound) bomb for attacks on Allied vessels. Although many Kamikazes were shot down, many got through American defenses and inflicted great damage on US Navy warships. Zeroes were also used for home defense against American bomber raids, and apparently some A6M5s were field-modified with a single upward-firing 20-millimeter cannon to operate as ineffectual night fighters.

Mitsubishi did manage to design two final variants of the Zero. The first was the "A6M7" or "Model 63", which had the Sakae 31a engine and five-gun armament, and could carry a 500-kilogram (1,100-pound) or a 250-kilogram (550-pound) bomb under the centerline, along with two underwing tanks. It first flew in May 1945, and was intended for the attack or Kamikaze role.

Mitsubishi A6M3 & A6M8

The second was the "A6M8", which was to be fitted with a Mitsubishi Kinsei 62 engine with 1,000 kW (1,340 HP), giving it a top speed of almost 575 KPH (360 MPH). Ironically, Horikoshi had wanted to use the Kinsei engine from the beginning, but the IJN had regarded it as too powerful. The larger engine dictated elimination of the 13.2-millimeter gun mounted in the cowling, with the four guns in the wings retained, and an improved fuel-tank fire extinguishing system was fitted. Two new-build prototypes were flown in the summer of 1945, but by that time it was a case of "much too little and far too late." It did not enter production before the war ended in August, after almost 10,500 Zeroes of all types had been produced.



* During the war, a number of combatants mounted floats on fighters in the belief that such aircraft might be useful in island-fighting campaigns. The Americans produced a floatplane Grumman Wildcat and the British developed a floatplane Spitfire.

The Japanese were the most enthusiastic about the concept. Well before Pearl Harbor, in the fall of 1940, Kawanishi had received a contract for an advanced floatplane fighter, the "N1K1 Kyofu (Mighty Wind)", but development proved troublesome and the Japanese decided to acquire an interim floatplane fighter, based on the A6M2.

Nakajima performed second-source production of the Zero, and in fact eventually built more than Mitsubishi, with a total of a over 6,500 Zeros built by Nakajima and a little under 4,000 built by Mitsubishi. Nakajima accordingly designed the floatplane variant of the Zero, with this variant first flying on the day Pearl Harbor was attacked, 7 December 1941.

The "A6M2-N" or "Type 2 Floatplane Fighter Model 11" as it was known, was basically a standard A6M2 with the undercarriage replaced by a centerline float, plus an outrigger float on each wing, and provided with a larger tailfin plus a small "strake" underneath the tail to compensate for aerodynamic clutter of the float system. While it couldn't carry a centerline drop tank, an additional fuel tank was installed in the central float itself.

Nakajima A6M2-N

Nakajima produced 327 A6M2-Ns through September 1943. Although the floats did reduce performance, it was fast for a floatplane and retained much of the A6M2's maneuverability, allowing it to surprise overconfident Allied pilots on occasion. However, it was still outclassed and had little impact on the war.

   _____________________   _________________   _______________________
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                12 meters           39 feet 5 inch
   wing area               22.44 sq_meters     241.54 sq_feet   
   length                  10.1 meters         33 feet 2 inches
   height                  4.3 meters          14 feet 1 inches

   empty weight            1,912 kilograms     4,235 pounds
   loaded weight           2,460 kilograms     5,423 pounds

   max speed at altitude   435 KPH             270 MPH / 235 KT
   service ceiling         10,000 meters       32,800 feet
   range                   1,775 kilometers    1,100 MI / 960 NMI
   _____________________   _________________   _______________________

The Kawanishi N1K1 Kyofu did reach production in mid-1943, but by that time Japanese priorities had changed greatly. Only a handful of Kyofus were built, with production focusing on the "N1K1-J Shiden (Violet Lightning)", a version of the Kyofu with normal retractable undercarriage, and the largely redesigned "N1K2-J Shiden-kai".

* Another footnote to the Zero story was the development of a tandem two-seat dual-control trainer, the "A6M2-K", intended for the advanced trainer role. The wing cannon and the fuselage fuel tank were deleted to reduce weight and permit installations of the two-seat cockpit. The wheel covers were also deleted, and small strakes were fitted ahead of the tailplane to compensate for the revised aerodynamics caused by the long cockpit. The first A6M2-K was completed in November 1943.

236 A6M2-Ks were built by the Naval Air Arsenal at Sasebo and 272 were built by Hitachi, for a total of 508 machines. Seven experimental trainer variants of the A6M5, of course designated "A6M5-K", were built as well, raising the total production of Zero trainers to 515. Some of the trainers were used as target tugs, and unsurprisingly, as Kamikazes.



* The fact that the Zero was not a miraculous design is emphasized by the fact that in the late 1930s, the British designed and flew a fighter that was strikingly similar to the Zero.

Gloster F.5/34

The Zero look-alike was built by Gloster in response to the British Air Ministry requirement "F.5/34", which also produced the Hawker Hurricane and the Supermarine Spitfire. Like the Zero, the Gloster F.5/34 contender was a low-wing all-metal monoplane with an air-cooled radial engine. The engine was the nine-cylinder Mercury IX with 625 kW (840 HP). The aircraft was to be armed with eight 7.7-millimeter (0.303-caliber) Browning machine guns.

   GLOSTER F.5/34:
   _____________________   _________________   _______________________
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                11.63 meters        38 feet 2 inches
   wing area               21.36 sq_meters     230 sq_feet   
   length                  9.76 meters         32 feet
   height                  3.09 meters         10 feet 2 inches

   empty weight            1,900 kilograms     4,190 pounds
   loaded weight           2,450 kilograms     5,400 pounds
   max speed at altitude   508 KPH             316 MPH / 275 KT
   _____________________   _________________   _______________________

Gloster put no great effort into the design, and in fact never even gave it a name or designation besides the F.5/34 requirement code. One prototype flew in December 1937, with a second following in March 1938. Gloster then dropped out of the competition and filed the work away.

Performance of the Gloster F.5/34 was comparable to that of early model Zeros, and the dimensions were remarkably close to that of the Zero, though the British aircraft was slightly heavier, had a shorter wingspan, and a longer fuselage. Exactly how the F.5/34 stacked up against the Zero would take a comparative evaluation that was never performed, and is now beyond useful speculation.

* Although the Gloster F.5/34 flew well before the first flight of the Zero, that does not imply that the Zero was a derivative of a British design. The Gloster aircraft was obscure and it is unlikely the Japanese knew much about it, and besides, the two machines were entirely different in detail.

In fact, during the war, Allied intelligence repeatedly suggested that the Zero was a copy of various other types of foreign aircraft, such as the Howard Hughes 1935 air racer and particularly the Vought 143, a one-off prototype fighter that the Japanese purchased. That was a stretch, since the Vought 143 really didn't look that much like a Zero and was a detestable aircraft in the first place; the idea that a fine machine like the Zero was a copy of it strained all logic. According to Horikoshi, the influence of the Vought 143 on the Zero was limited to the design of the landing gear.

The idea that the Zero was a copy of a Western aircraft appears to have been mostly chauvinism, based on the preconception, which still persists today, that the Japanese are only capable of copying other people's ideas. In fact, although the Japanese pragmatically do not hesitate to copy good ideas developed elsewhere, the Zero proved they could make their own contributions as well. In the case of the Zero, Horikoshi later provided an articulate and detailed argument to reject that it was a copy of any foreign aircraft. True, the engine was derived from the Pratt & Whitney Twin Wasp, the propeller was a Hamilton Standard design, the flight instruments were copies or license builds of foreign designs, and the guns were all basically licensed foreign designs as well -- but such technology trading was common in the design of aircraft of other nations.

The Zero was a Japanese design and had significant merits, representing a clever compromise between capability and limited engine power. It had a time of glory when it ruled the skies. If it did not prove to be a miracle machine over the long run, much the same could be said of fighters of other combatants that served on long after they were obsolete.



* Zero variants include:



* A number of other Zeros were captured by the Americans after the recovery of Koga's Zero in the summer of 1942, including a dozen A6M5s obtained after the fall of Saipan. A Grumman test pilot named Corwin H. "Corky" Meyer flew an A6M5a in October 1944 at a conference where the latest American, British, and captured enemy fighters were evaluated by test pilots in attendance.

Much later, Meyer wrote an interesting memoir of his flights. Meyer said the Zero looked "every bit the fighter" and regarded it as the "best looking fighter at the meet." He found it a delight to fly, and was surprised at the quality of manufacture, since in America at the time, and indeed well into the 1960s, "made in Japan" was the same as saying "junk". "The workmanship was superb and comparable to American quality. This was most amazing in light of the prewar Japanese products with which most of us had come in contact."

Meyer noticed that the Sakae 21 engine announced its Pratt & Whitney ancestry by conscientiously displaying the Pratt & Whitney logo with an eagle on it and the English term "Quality & Reliability", along with the Nakajima name in Japanese. Although Meyer was 190 centimeters (6 foot 3 inches) tall, taller than any Japanese pilot, he found the cockpit surprisingly comfortable, though his feet felt tucked under him. He found one detail particularly interesting:


Another un-American feature that must have given Japanese pilots mixed emotions was the protrusion of the 7.7-millimeter-type (0.303-caliber) gun butts six inches [15 centimeters] into the cockpit on either side of the instrument panel. I'm sure they gave a very macho feeling to the pilots when firing, with the racket, the nearness of the action, and the ability to unsort guns manually. With all the cordite fumes, I do hope the Japanese pilots had good 100% oxygen masks. Also, the gun butts must have been most disconcerting and disfiguring in a crash.


It is thought that Charles Lindbergh also flew a captured Zero. Some of the captured Zeroes ended up in US air museums after the war, but Koga's Zero wasn't among them. In February 1945, while the Zero was being taxied, a Curtiss Helldiver dive-bomber ran into it and thoroughly chopped it up with its propeller, the pilot of the Zero narrowly escaping injury. Given the bad reputation of the SB2C Helldiver, also known as "Beast" and "Son of a Bitch Second Class", somehow such a clumsy act seems unsurprising.

* Only about 16 Zeroes survive today, and only a few of them are in flying condition. Restoring a Zero is troublesome because the lightweight ESD alloy heavily used in its construction tended to crystallize over time, losing its structural strength. Of course, the Zero's specifications never stated that the aircraft was to remain flightworthy into the next century. Only one of the flight-worthy machines actually is fitted with the Sakae engine; the others use a Pratt & Whitney R-1830 engine.

A number of flyable Zero replicas exist. These were modified from North American AT-6 Texans for the 1969 movie "TORA TORA TORA", about the Japanese attack on Pearl Harbor. The replicas are surprisingly convincing, though they are still clearly fakes, since the Texan is a chubbier aircraft than the slender Zero. 25 of these bogus Zeroes were built; how many remain flying is unclear.

* Actual production quantities of the various models of Zeroes appears to be very difficult to nail down, with some sources claiming that relevant Japanese government and industry documentation is inconsistent on the matter, which seems very believable. While "official" documentation has to be regarded as more or less the definitive word on such subjects, it is worthwhile to remember that the official word isn't always correct either.

Another comment is that Japanese aircraft are often referred to in literature by their Allied codenames, with the A5M4 known as "Claude"; the Zero generally known as "Zeke", except for the A6M3, which was sometimes called "Hamp"; and the Nakajima floatplane Zero known as "Rufe". That is not wrong, the only problem is that the naming scheme didn't catch on until late in 1943, and it's unclear if it was universally used after that. It appears that the codenames are more important in memory than they were at the time; German aircraft were also given codenames, but they didn't stick. Instead of fussing with the issue, it seemed wiser just to mention that the names existed and leave it at that.

Mitsubishi A6M Zero

Two final comments:

* As concerns copyrights and permissions for this document, all illustrations and images credited to me are public domain. I reserve all rights to my writings. However, if anyone does want to make use of my writings, just contact me, and we can chat about it. I'm lenient in giving permissions, usually on the basis of being properly credited.

* Sources include:

The old Profile documents by Dr. Francillon were very interesting, partly because he had consulted with Horikoshi Jirou in their production. One interesting detail was that when Francillon asked Horikoshi about the A6M4, he couldn't remember what it was at first, though he was eventually able to come up with some relevant documentation.

This illustrates the principle that even an amateur historian quickly learns: history is not so much about the past as it is about records of the past, that may or may not reflect what really happened. Even when written down, there is no guarantee that the realities of things were recorded accurately, or even that the documentation wasn't written to conceal the truth instead of record it.

* Revision history:

   v1.0   / 01 may 00
   v1.1   / 01 oct 00 / Review & polish.
   v1.2   / 01 feb 01 / Review & polish.
   v1.3.0 / 01 aug 03 / Added variant list, more A5M comments, ETC.
   v1.3.1 / 01 aug 05 / Review & polish.
   v1.3.2 / 01 jul 07 / Review & polish.
   v1.3.3 / 01 jun 09 / Review & polish.
   v1.3.4 / 01 may 11 / Review & polish.
   v1.3.5 / 01 apr 13 / Review & polish.
   v1.3.6 / 01 mar 15 / Review & polish.
   v1.3.7 / 01 mar 15 / Review & polish.