Mitsubishi A6M Reisen Zero (Zeke, Hamp) was a long-range navy fighter. Original japanese designation: Mitsubishi Navy Type 0 Carrier Fighter (零式艦上戦闘機 rei-shiki-kanjō-sentōki) or Mitsubishi Navy 12-shi carrier fighter. Production: 10939 units.
The A5M Claude had just entered service in early 1937 when the Japanese Imperial Navy began searching for a possible successor. By May, specifications for a new carrier fighter had been drawn up and passed on to Nakajima and Mitsubishi. The two companies began their work while awaiting further information.
Based on the experience of the A5M in China, the Japanese Navy issued additional specifications in October, requiring 500 km/h at 4,000 metres and an climb speed of 6,000 m in 9 min 5 s. They needed a range of 2 hours at normal power, which was to be increased to 6 or 8 hours at economy speed with additional tanks. The armament was to include two 20 mm cannons and two 7.7 mm machine guns, and the aircraft was to be able to carry two 30 or 60 kg bombs. All future Zeros were to be equipped with radio equipment. Finally, manoeuvrability had to be at least as good as with the A5M, while the wingspan had to be less than 12 m to be able to fit on aircraft carriers.
Nakajima found the new requirements impossible to meet, while Mitsubishi’s team leader Jirō Horikoshi, who had already designed the A5M Claude, agreed that they could be met on the sole condition that the aircraft be as light as possible. So, every effort was made to save weight and the designers made extensive use of a new aluminium alloy, Extra Super Duraluminium (ESD) developed by Sumitomo Metals.
The first prototype of the Mitsubishi A6M flew as early as April 1, 1939 and production began in July of the same year.
With excellent manoeuvrability, high firepower (in 1940) and a very long range, the initial superiority of the Zero and its exceptional range would weigh heavily on the balance when the Japanese chose to launch the attack on Pearl Harbor.
In April 1938, the design offices of the Yokosuka Arsenal approved the 12 Shi fighter aircraft project and the construction of two prototypes was assigned to the aircraft producer Mitsubishi. The construction of the two prototypes, called A6M1/12 Shi, began in the summer of 1938. They were each equipped with a Mitsubishi Zuisei 13 engine of 780 hp, driving a two-blade propeller with variable pitch, but the engine did not give full satisfaction and this version, the first of the aircraft, was never produced in series. The Navy then suggested that the brand new 940 hp Nakajima Sakae 12 (NK1C) engine be fitted to two new prototypes. This engine was the equivalent of the Army’s Ha 25. The introduction of the new engine by far met the requirements of the original specification and the A6M2 model was ready for series production.
A6M2 model 11
The first fifteen copies of the pre-series were sent to China in July 1940 for evaluation in real field conditions. The engines of these aircraft tended to overheat. The problem had to be solved. While the aircraft had been designed to be used onboard, this first model was only going to be based on the mainland, so it was manufactured without its tail hook. The result was not long in coming, and the A6M2s swept everything in their path from the sky, so much so that the Chinese carefully avoided fighting the Zeros with their Polikarpov I-15 and I-16s. Westerners, who had the opportunity to take an interest in the Zero, continued to believe in the destitution of Japanese aviation. They were going to regret it.
A6M2 model 21
Because of their wingtips, the wingspan of the models 11 was disturbing for the manoeuvres in the elevators of the aircraft carriers, the first evolution of the Zero consisted thus in modifying the wing so that the wingtips are foldable: it will be the A6M2 model 21 (including 2nd type of airframe, 1st type of engine). Some details will evolve on the model 21, such as the appearance of an aileron counterweight to relieve the effort at high speed, a recurring problem on the Zero that will never really be corrected. This model, and most of the following models, was built with its tailhook. Located under the stabilizer, it was intended to stop the aircraft by hooking a arresting wires when landing on aircraft carriers.
A6M3 model 32 and 22
The A6M3 Model 32 was introduced in the spring of 1942 during the Battle of the Solomon Islands (Guadalcanal). Important modification: the 940 hp Nakajima Sakae 12 engine was replaced by a NK1F Sakae 21 or Ha-35-21, equipped with a two-speed supercharger delivering 1,130 hp at takeoff. This new, longer engine required the firewall to be moved 20 cm (8 inches) at the expense of fuel capacity. The engine cowling changed shape and the supercharger air intake was positioned at the top instead of the “tunnel” at the bottom. The guns had 100 shells each instead of the original 60. But the most noticeable change was the disappearance of the folding wing tips to improve the roll rate but also production. The Americans thought they were dealing with a new plane which they named Hamp instead of Zeke, but they quickly realized their mistake. The maximum speed went from 288 knots to 294 knots.
Production: at least 343 units
In an attempt to achieve a range comparable to the Model 21 following the increase in consumption of the Sakae 21 and the decrease in tank volume, Mitsubishi engineers installed two new 45-litre tanks in each wing. To maintain wing loading equivalent to Type 32, the folding wingtips were restored. Some 22 models received the 20 mm gun type 99 model 2 mark 3 with long barrel and improved rate of fire which one will find on the future versions. Three experimental models based in Rabaul used 30 mm cannons but no continuation will be given.
Production: 560 units
In the end, there was no Series 4, the A6M4 had to use a turbocharger that was never fully developed. The Japanese had a lot of problems with turbochargers throughout the war.
Still unable to develop the A7M Reppu (and especially struggling to make decisions), the Navy asked for an improved aircraft to make a junction that never took place. In August 1943, a Model 22 was modified by increasing the thickness of the wing skins, and reduced wing tip sizes were installed in a fixed position. In addition, the engine received separate exhaust pipes for propulsion. Although 70 kg heavier, the new Model 52 was 11 knots faster in level flight compared to the Model 32, but more importantly, its maximum dive speed was increased to 660 km/h. But these improvements were not enough and the Zero 52s were slaughtered by the Hellcats.
In March 1944, the Model 52 appeared on the front line. The further increase in the thickness of the surface allowed a dive speed of 740 km/h (the Corsair dive at 790 km/h). The mk4 guns received 125 shells each (instead of 100) by replacing the drums with belts.
The 52b model saw an improvement in the ability to take and return fire. A 50 mm armoured windscreen and tank extinguishers were installed. And a 13.2 mm Type 3 machine gun replaced one of the 7.7 mm.
The Model 52c was launched in emergency after the Battle of the Philippines. Despite the obsolescence of the airframe, it was necessary to improve the Zero because the production of the J2M Raiden did not start. The A6M5c incorporated back armour for the pilot, a self-sealing central tank and two 13.2 mm machine guns with 13.2 mm wings on the outside of the guns. The 7.7 mm machine gun on the cowling disappeared. The engineers asked the Navy for the right to install the larger Mitsubishi Kinsei engine to deal with the expected increase in weight. Once again, the Navy, by an incredible inertia, refused again and forced the Sakae 21 until the Sakae 31 was available, whose power had to be increased by injecting water and methanol. The performance collapsed.
A night fighter was developed from the model 52 by adding an angled gun in the fuselage. It was the A6M5d-S, S being the suffix of the night fighters (example J1N1-S Gekko).
Production: model 52: more than 747 units, model 52a: more than 391 units, model 52b: 470 units, model 52c: 93 units.
First training version, two-seater. The airframe was modified so that the cockpit and canopy could house an instructor and an apprentice pilot. The motorization remained the same as that of the other versions of A6M; in the armament, the wing cannons of 20 mm were removed and only the two 7,7 mm machine guns. 60 kg bombs could be carried under the wings during training, but when these aircraft were used as Kamikazes in 1945, the 60 kg bombs were replaced by a 250 kg bomb. The production was divided between 236 units made by Dai-Nijuichi Kaigun Kokusho at Ōmura (Sasebo) between November 1943 and August 1945 and 272 units were made by Hitachi Kokuki K. K. between May 1944 and August 1945. Production: 508 units.
Second training version, of which only seven were made by Hitachi Kokuki K. K. between March and August 1945. Same motorization as the A6M5 and same armament as the previous training version (A6M2-K): two 7.7 mm machine guns and two 60 kg bombs.
The prototype of the A6M6 (Zero 53) flew in November 1944. In addition to the Sakae 31 engine (whose power greater than the 1,130 hp of the Sakae 21 is not mentioned in any book), the 45 l wing tanks received a self-sealing coating. The maximum speed of 300 knots (5 less than the 52), using water injection, was only theoretical, as the quality of engine and airframe manufacture was dangerously low due to the lack of quality raw materials and the lack of skilled labour. Skilled workers were recruited into the army. Moreover, the B-29 Superfortress raids on the engine factories were not going to help.
Production: only one prototype, according to some sources.
The combat units modified the central tank racks to hold a 250 kg bomb on the previous versions. This will be standard on the A6M7 model 63.
Intended to be used as a dive bomber, the Model 63 had a bomb holder and attachment points for two 350-litre outer wing tanks and a tailplane with a thickened skin to resist stress. Production began in May 1945.
As Nakajima was concentrating on producing the powerful 2,000 hp 18-cylinder Nakajima Homare engine, which had become a priority, production of the Nakajima Sakae had to be stopped slowly. Mitsubishi was then finally allowed to use the reliable and powerful 14-cylinder MK8P Mitsubishi Kinsei 62 [Ha-33]-62 engine with 1,560 hp.
This proven powerplant had been efficiently adapted to the Air Force Ki-100 and the Navy D4Y (from D4Y3 onwards). As the Kinsei was larger, it required a new cowling and the cowling machine gun disappeared. Since the beginning of the program, the power-to-weight ratio finally increased. The first prototype was finished in April 1945 and the encouraging results led the Navy to order no less than 6,300 A6M8s! However, none of them would see combat because the stagnation caused by the bombings and the shortage of materials had totally disrupted production. Prototypes of the A6M8 used 52c airframes, hence the name Zero 54, but the production models had to use the model 63 airframe, hence the name Zero 64.
Production: 6,300 planned, no production copies, 2 prototypes.
Seaplane fighter plane. A float with an extra fuel tank was added under the fuselage, and each wing carried a smaller one under its underside. The Rufe, as it was code-named by the Allies, had the same armament as the other variants: two 7.7 mm machine guns on the cowling and two 20 mm guns, one in each wing.
Production: 327 units
Designed for attack, the Zero was a model of maneuverability and firepower and had a great autonomy in flight, an essential asset for the Japanese naval forces during the conquest phase and in the hands of the over-trained pilots at the beginning of the war it was very effective. But like many Japanese aircraft, its most important weaknesses were the lack of protection for the pilot and the self-sealing tanks, which increased the losses and then was an insurmountable handicap for the hastily trained pilots who found themselves in the front line as early as the autumn of 1942 following the losses of the Battle of Midway and the Guadalcanal campaign. On the last two versions, however, it benefited from some improvements but the results, due to a lack of mastery, were disappointing.
Many Zeros were also lost in battle as soon as the Allies abandoned dogfighting for the “yoyo” or “Thach Weave”, a tactic created by John Thach (horizontal or vertical maneuver, consisting of two aircraft to move away and then return, thus protecting the teammate by promoting the destruction of his pursuer) and the dive and zoom – dive attack then return – favorable to the American aircraft heavier by their armor and more powerful engines.
When the Americans mastered the Zero attack techniques, thanks in part to Akutan’s Zero, the ratio of 1 Japanese plane shot down for 1 American plane increased to 10 to 1.
However, the Japanese did not stay passive and launched new aircraft such as the Kawanishi N1K1-J Shiden (Purple Lightning) “George” and especially the excellent Nakajima Ki-84 Hayate “Frank”.
The first being a land-based version of a seaplane and the second, an Air Force fighter, they were the last symbols of the change of strategy in favour of ground-based aircraft, due to the lack of aircraft carriers.
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