The Mitsubishi A6M Zero was a long-range carrier-based fighter aircraft formerly manufactured by Mitsubishi Aircraft Company, a part of Mitsubishi Heavy Industries, and operated by the Imperial Japanese Navy from 1940 to 1945.
The A6M was designated as the Mitsubishi Navy Type 0 carrier fighter, or the Mitsubishi A6M Reisen.
The A6M was usually referred to by its pilots as the Reisen (zero fighter), “0” being the last digit of the imperial year 2600 (1940) when it entered service with the Imperial Navy.
The official Allied reporting name was “Zeke”, although the name “Zero” (from Type 0) was used colloquially as well.
The Zero is considered to have been the most capable carrier-based fighter in the world when it was introduced early in World War II, combining excellent manoeuvrability and very long range.
The Imperial Japanese Navy Air Service (IJNAS) also frequently used it as a land-based fighter.
In early combat operations, the Zero gained a reputation as a dogfighter, achieving an outstanding kill ratio of 12 to 1, but by mid-1942 a combination of new tactics and the introduction of better equipment enabled Allied pilots to engage the Zero on generally equal terms.
By 1943, the Zero was less effective against newer Allied fighters due to design limitations.
It lacked hydraulic boosting for its ailerons and rudder, rendering it extremely difficult to manoeuvre at high speeds.
By 1944, with Allied fighters approaching the A6M levels of manoeuvrability and consistently exceeding its firepower, armour, and speed, the A6M had largely become outdated as a fighter aircraft.
However, as design delays and production difficulties hampered the introduction of newer Japanese aircraft models, the Zero continued to serve in a front-line role until the end of the war in the Pacific.
During the final phases, it was also adapted for use in kamikaze operations.
Japan produced more Zeros than any other model of combat aircraft during the war.
The Mitsubishi A5M fighter was just entering service in early 1937, when the Imperial Japanese Navy (IJN) started looking for its eventual replacement.
On 5 October 1937, it issued “Planning Requirements for the Prototype 12-shi Carrier-based Fighter”, sending it to Nakajima and Mitsubishi.
Both firms 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 IJN sent out updated requirements in October calling for a speed of 270 kn (310 mph: 500 km/h) at 4,000 m (13,000 ft) and a climb to 3,000 m (9,800 ft) in 9.5 minutes.
With drop tanks, it wanted an endurance of two hours at normal power, or six to eight hours at economical cruising speed.
Armament was to consist of two 20 mm cannons, two 7.7 mm (.303 in) machine guns and two 60 kg (130 lb) bombs.
A complete radio set was to be mounted in all aircraft, along with a radio direction finder for long-range navigation.
The manoeuvrability was to be at least equal to that of the A5M, while the wingspan had to be less than 12 m (39 ft) to allow for use on aircraft carriers.
Nakajima’s team considered the new requirements unachievable and pulled out of the competition in January. Mitsubishi’s chief designer, Jiro Horikoshi, thought that the requirements could be met, but only if the aircraft were made as light as possible.
Every possible weight-saving measure was incorporated into the design.
Most of the aircraft was built of a new top-secret aluminium alloy developed by Sumitomo Metal Industries in 1936. Called “extra super duralumin” (ESD), it was lighter, stronger and more ductile than other alloys (e.g., 24S alloy) used at the time, but was prone to corrosive attack, which made it brittle.
This detrimental effect was countered with an anti-corrosion coating applied after fabrication.
No armour protection was provided for the pilot, engine or other critical points of the aircraft, and self-sealing fuel tanks, which were becoming common among other combatants, were not used.
This made the Zero lighter, more manoeuvrable, and the longest-ranged single-engine fighter of World War II, which made it capable of searching out an enemy hundreds of kilometres away, bringing it to battle, then returning to its base or aircraft carrier.
However, that trade-off in weight and construction also made it prone to catching fire and exploding when struck by enemy fire.
With its low-wing cantilever monoplane layout, retractable, wide-set conventional landing gear and enclosed cockpit, the Zero was one of the most modern carrier-based aircraft in the world at the time of its introduction.
It had a fairly high-lift, low-speed wing with very low wing loading.
This, combined with its light weight, resulted in a very low stalling speed of well below 60 kn (110 km/h; 69 mph).
This was the main reason for its phenomenal manoeuvrability, allowing it to out-turn any Allied fighter of the time.
Early models were fitted with servo tabs on the ailerons after pilots complained that control forces became too heavy at speeds above 300 kilometres per hour (190 mph).
They were discontinued on later models after it was found that the lightened control forces were causing pilots to overstress the wings during vigorous manoeuvres.
A6M1, Type 0 Prototypes
The first two A6M1 prototypes were completed in March 1939, powered by the 580 kW (780 hp) Mitsubishi Zuisei 13 engine with a two-blade propeller.
It first flew on 1 April and passed testing within a remarkably short period.
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.
A6M2a Type 0 Model 11
While the navy was testing the first two prototypes, they suggested that the third be fitted with the 700 kW (940 hp) 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 Zero 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-16s and I-153s that had been such a problem for the A5Ms when in service.
In one encounter, 13 Zeros shot down 27 I-15s and I-16s in under three minutes without loss.
After hearing of these reports, the navy immediately ordered the A6M2 into production as the Type 0 Carrier Fighter, Model 11.
A6M2b Type 0 Model 21
After the delivery of the 65th aircraft, a further change was worked into the production lines, which introduced folding wingtips to allow them to fit on aircraft carriers.
The resulting Model 21 would become one of the most produced versions early in the war.
A feature was the improved range with 520 l (140 US gal) wing tank and 320 l (85 US gal) drop tank.
When the lines switched to updated models, 740 Model 21s had been 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 modified 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
A6M3 Model 32.
In 1941, Nakajima introduced the Sakae 21 engine, which used a two-speed supercharger for better altitude performance, and increased power to 840 kW (1,130 hp).
A prototype Zero with the new engine was first flown on 15 July 1941.
The new Sakae was slightly heavier and somewhat longer due to the larger supercharger, which moved the centre of gravity too far forward on the existing airframe.
To correct for this, the engine mountings were cut back by 185 mm (7.3 in) to move the engine toward the cockpit.
This had the side effect of reducing the size of the main fuselage fuel tank (located between the engine and the cockpit) from 518 l (137 US gal) to 470 l (120 US gal).
The cowling was redesigned to enlarge the cowl flaps, revise the oil cooler air intake, and move the carburettor air intake to the upper half of the cowling.
The wings were redesigned to reduce span, eliminate the folding tips, and square off the wingtips.
The inboard edge of the aileron was moved outboard by one rib, and the wing fuel tanks were enlarged accordingly to 420 l (110 US gal).
The two 20 mm wing cannon were upgraded from the Type 99 Mark l to the Mark II, which required a bulge in the sheet metal of the wing below each cannon.
The wings also included larger ammunition boxes and thus allowing 100 rounds per cannon.
The Sakae 21 engine and other changes increased maximum speed by only 11 km/h (6.8 mph) compared to the Model 21 but sacrificed nearly 1,000 km (620 mi) of range.
Nevertheless, the navy accepted the type, and it entered production in April 1942.
This variant was flown by only a small number of units, and only 343 were built.
A6M3 Type 0 Model 22
In order to correct the deficiencies of the Model 32, a new version with folding wingtips and redesigned wing was introduced.
The fuel tanks were moved to the outer wings, fuel lines for a 330 l (87 US gal) drop tank were installed under each wing and the internal fuel capacity was increased to 570 l (150 US gal).
More importantly, it regained its capabilities for long operating ranges, similar to the previous A6M2 Model 21, which was vastly shortened by the Model 32.
However, before the new design type was accepted formally by the Navy, the A6M3 Model 22 already stood ready for service in December 1942.
Approximately 560 aircraft of the new type had been produced in the meantime by Mitsubishi Jukogyo K.K.
The Model 32, 22, 22 kou, 52, 52 kou and 52 otsu were all powered by the Nakajima (Sakae) 21 engine.
That engine kept its designation in spite of changes in the exhaust system for the Model 52.
A6M4 Type 0 Model 41/42
Some researchers believe “A6M4” was applied to one or two prototype planes fitted with an experimental turbo-supercharged Sakae engine designed for high altitude.
Mitsubishi’s involvement in the project was quite limited, as the unmodified Sakae engine was made by Nakajima.
The design and testing of the turbo-supercharger was the responsibility of the First Naval Air Arsenal.
The prototype engines nevertheless provided useful experience for future engine designs.
A6M5 Type 0 Model 52
Produced first by Mitsubishi, most Model 52s were made by Nakajima.
The prototype was made in June 1943 by modifying an A6M3 and was first flown in August 1943.
Nakajima manufactured the Model 52 at its Koizumi plant in Gunma Prefecture.
Subsequent variants included:
A6M5a, Model 52, Kō, 52a
Starting at Mitsubishi number 4651, an armament change substituted the belt-fed Type 99-2 Mark 4 cannon, with 125 rounds per gun, in place of the drum-fed Type 99-2 Mark 3 cannon that carried 100 rounds per gun.
A6M5b, Model 52, Otsu, 52b
Armament change, The first of this variant was completed in April 1944 and it was produced until October 1944.
A6M5c, Model 52, Hei, 52c
Armament change, the first of this variant was completed in September 1944, it was used mainly for intercepting B-29s and special attack.
A6M5-S, A6M5 Yakan Sentōki
Armament change, to intercept B-29s and other night-flying aircraft, an air arsenal converted some Model 52s to night fighters.
A6M6 Type 0 Model 53
Only one prototype was produced.
A6M7 Type 0 Model 62/63
Entering production in May 1945, the A6M7 was also used in the special attack role.
A6M8 Type 0 Model 64
Two prototypes were completed in April 1945, but the chaotic situation of Japanese industry and the end of the war obstructed the start of the ambitious program of production for 6,300 A6M8s, only the two prototypes being completed and flown.