Mitsubishi A6M Zero

Mitsubishi A6M2 "Zero" Model 21 (cowling removed)

The Mitsubishi A6M was a light-weight carrier-based fighter aircraft employed by the Japanese Navy from 1940 to 1945.

While the official Allied code name was Zeke, it is universally known as Zero from its Japanese Navy designation, Type 0 Carrier Fighter (零式艦上戦闘機), taken from the Imperial year 2600 (1940). It was also known as a Tojo Zero.

A combination of excellent manuverability and very long range made it the best fighter of its era and gained it a legendary reputation, but design weaknesses and lack of more powerful engines eventually doomed it.

History

The Mitsubishi A5M was just starting to enter service in early 1937 when the IJN started looking for its eventual replacement. In May they issued specification 12-Shi for a new carrier based fighter, sending it to Nakajima and Mitsubishi. Both started preliminary design work while they awaited more definitive requirements to be handed over in a few months.

Based on the experiences of the A5M in China, the Navy sent out updated requirements in October. The new requirements called for a speed of 500 km/h at 4000 m, and a climb to 3000 m in 3.5 min. They needed an endurance of 2 hours at normal power, or 6 to 8 hours at economical cruising speed (both with drop tanks). Armament was to consist of two 20 mm cannons and two 7.7 mm machine guns, and two 30 kg or 60 kg bombs. A complete radio set was to be mounted in all planes, along with a radio direction finder for long-range navigation. Finally the maneuverability was to be at least equal to A5M, while the wing span had to be less than 12 m to fit on the carriers.

Nakajima's team thought the new requirements were ridiculous and pulled out of the competition in January. Mitsubishi's chief designer, Jiro Horikoshi, felt that the requirements could be met, but only if the aircraft could be made as light as possible. Every weight saving method was used, and the designers made extensive use of the new duralumin alloy. With its low-wing cantilever monoplane layout, retractable wide-set landing gear and enclosed cockpit, the design was not only much more modern than any the Navy had used in the past, it was one of the most modern in the world.

At the time of Pearl Harbor there were only 420 Zeros active in the Pacific. The carrier borne Model 21 was the type encountered by the Americans, often much further from its carriers than expected, with a mission range of over 1600 miles (2,600 km). They were superior to all current Allied fighters in the Pacific and remained unchallenged until early 1943, although in competent hands the Zero was still deadly at the end of the war. Because of their reputation and ease of manufacture the Zero remained in production until the end, with over 11,000 of all types produced.

Designed for attack the Zero gave precedence to manoeuvrability and fire-power at the expense of protection - most had no self-sealing tanks or armour plate - thus many Zeros were lost too easily in combat. Nevertheless, many Allied pilots died trying to learn how to fight such an agile aircraft.

It was not until new tactics were developed that US pilots were able to fight the Zero with any measure of equality. The correct combat tactic against Zeros was to remain out of range and fight on the dive and climb. By using speed and resisting the deadly error of trying to out-turn the Zero, eventually cannon could be brought to bear and a single burst of fire was usually enough. Another important maneuver was called the "Thatch Weave," named for the man that invented it. It required two planes, a leader and his wingman, to fly about 200 feet apart. When a Zero would latch onto the tail of one of the fighters, the two planes would turn toward each other. If the Zero followed its original target through the turn, it would come into a position to be fired on by his target's wingman. This tactic was used with spectacular results at the Battle of the Coral Sea and at the Battle of Midway, and helped make up for the inferiority of the US planes until new aircraft types were brought into service.

When the US had learned the "secret" of the Zero new aircraft such as the Grumman Hellcat and Vought Corsair were introduced, planes that outperformed the Zero in every way but maneuverability. To correct that shortcoming, US pilots had to apply the correct tactics. The result was that the US Navy's 1:1 kill ratio suddenly jumped to better than 10:1. However Japanese development did not remain static - newer planes like the George were excellent fighters and a match for the later US models.

Variants

A6M1, Type 0 Prototypes

The first A6M1 prototype was completed in March 1939, powered by the 780 hp (580 kW) Mitsubishi Zuisei 13 engine with a two-bladed propeller. It first flew on April 1st, and passed testing in a remarkably short period of time. By September it had already been accepted for Navy testing as the A6M1 Type 0 Carrier Fighter, with the only notable change being a switch to a three-bladed propeller to cure a vibration problem.

A6M2, Type 0 Model 11

While the Navy was testing the first two prototypes, they suggested that the third be fitted with the 940 hp (700 kW) Nakajima Sakae 12 engine instead. Mitsubishi had its own engine of this class in the form of the Kinsei, so they were somewhat reluctant to use the Sakae. Nevertheless when the first A6M2 was completed in January 1940, the Sakae's extra power pushed the performance of the plane well past the original specifications.

The new version was so promising that the Navy had 15 built and shipped to China before they had completed testing. They arrived in Manchuria in July 1940, and first saw combat over Chungking in August. There they proved to be completely untouchable by the Polikarpov I-16's and I-153s that had been such a problem for the A5M's currently in service. In one encounter 13 Zeros shot down 27 I-15 and I-16's in under three minutes without loss. After hearing of these reports the Navy immediately ordered the plane into production as the Type 0 Carrier Fighter, Model 11.

Reports of the Zero's performance filtered back to the US slowly. There they were dismissed by most planners, who felt it was impossible for the Japanese to build such an aircraft. Others were not so sure, and techniques were developed by Butch O'Hare to combat them just in case.

A6M2, Type 0 Model 21

After the delivery of only 65 planes by November 1940, a further change was worked into the production lines, which introduced folding wingtips to allow them to fit on the aircraft carriers. The resulting Model 21 would become one of the most produced versions early in the war. When the lines switched to updated models, 740 Model 21's were completed by Mitsubishi, and another 800 by Nakajima. Two other versions of the Model 21 were built in small numbers, the Nakajima-built A6M2-N "Rufe" floatplane (based on the model 11 with a slightly modifed tail), and the A6M2-K two-seat trainer of which a total of 508 were built by Hitachi and the Sasebo Naval Air Arsenal.

A6M3, Type 0 Model 32

In late 1941 Nakajima introduced the Sakae 21, which used a two speed supercharger for better altitude performance, and increased power to 1,130 hp (840 kW). Plans were made to introduce the new engine into the Zero as soon as possible.

The new Sakae was slightly heavier and somewhat longer due to the larger supercharger, which moved the center of gravity too far forward on the existing airframe. To correct for this the engine mountings were cut down by 8 inches (200 mm), moving the engine back towards the cockpit. This had the side effect of reducing the size of the main fuel tank (located to the rear of the engine) from 518 litres to 470 litres.

The only other major changes were to the wings, which were simplified by removing the Model 21's folding tips. This changed the appearance enough to prompt the US to designate it with a new code name Hamp, before realizing it was simply a new model of the Zeke. The wings also included larger ammunition boxes, allowing for 100 rounds for each of the 20 mm cannon.

The wing changes had much a greater effects on performance than expected. The smaller size led to better roll, and their lower drag allowed the diving speed to be increased to 360 knots (670 km/h). On the downside, manuverability was reduced, and range suffered both due to decreased lift and the smaller fuel tank. Pilots complained about both. The shorter range proved a significant limitation during the Solomons campaign of 1942.

The first Model 32 deliveries began in April 1942, but it remained on the lines only for a short time, with a run of 343 being built.

A6M3, Type 0 Model 22

In order to correct the deficiencies of the Model 32, a new version with the Model 21's folding wings, new in-wing fuel tanks and attachments for a 330 litre drop tank under each wing was introduced. The internal fuel was thereby increased to 570 litres in this model, gaining back all of the lost range.

As the airframe was reverted from the Model 32 and the engine remained the same, this version received the navy designation Model 22, while Mitsubishi called it the A6M3a. The new model started production in December, and 560 were eventually produced.

A6M4

The A6M4 is a subject of some debate. Most sources refer to an experimental turbocharged version of the Zero for high altitude use, but only a single mention of the A6M4 can be found in text and it does not mention much.

A6M5, Type 0 Model 52

The A6M5 was a modest update of A6M3 Model 22, with wings with nonfolding tips and thicker skinning to permit faster diving speeds, plus an improved exhaust system (four pipes on each side) that provided an increment of thrust. Subvariants included the "A6M5a Model 52a", featuring cannon with belt feed instead of drum feed, permitting a bigger ammunition supply; the "A6M5b Model 52b", with an armor glass windscreen, a fuel tank fire extinguisher, and one 7.7 millimeter gun in the cowling replaced by a 13.2 millimeter Browning-pattern gun; and the "A6M5c Model 52c", with but with more armor plate and armament of three 13 millimeter guns (one in the cowling, one in each wing) and twin 20 millimeter guns.

A6M6c

This was similar to A6M5c, but with self-sealing wing tanks and a Nakajima Sakae 31a engine featuring water-methanol engine boost.

A6M7, Type 0 Model 63

Similar to A6M6 but intended for attack or Kamikaze role.

A6M8

Similar to A6M6 but with Mitsubishi Kinsei 62 engine, two prototypes built.

Specifications

General characteristics (A6M2 Model 21)

• Wing span : 39 ft (12 m)
• Length : 29 ft 9 in (9 m)
• Engine : 925 hp (690 kW)
• Max weight : 5,300 lb (2,400 kg)
• Armament : 2 x 7.7 mm MG, 2 x 20 mm cannon; 2 x 66 lb (30 kg) or 1 x 132 lb (60 kg) bombs; 2 fixed 250 kg bombs for kamikaze

Performance

• Max Speed : 336 mph at 20,000 ft (540 km/h at 6,000 m)
• Ceiling : 33,500 ft (10,000 m)

Related content
Related Development	Nakajima A6M2-N
Similar Aircraft	Grumman Wildcat
Designation Series	A3N - A4N - A5M - A6M - A7M
Related Lists	List of military aircraft of Japan - List of fighter aircraft