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Additional Information from Internet Encyclopedia

The Mitsubishi A6M "Zero" is a long-range fighter aircraft, manufactured by 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 (, rei-shiki-kanj�-sent�ki), or the Mitsubishi A6M Rei-sen. 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 use of the name "Zero" was later commonly adopted by the Allies as well.

When it was introduced early in World War II, the Zero was considered the most capable carrier-based fighter in the world, combining excellent maneuverability and very long range. The Imperial Japanese Navy Air Service ("IJNAS") also frequently used the type as a land-based fighter.

In early combat operations, the Zero gained a legendary reputation as a dogfighter, achieving the outstanding kill ratio of 12 to 1, but by mid-1942 a combination of new tactics and the introduction of better equipment enabled the Allied pilots to engage the Zero on generally equal terms. By 1943, inherent design weaknesses and the failure to develop more powerful aircraft engines meant that the Zero became less effective against newer enemy fighters, which possessed greater firepower, armor, and speed, and approached the Zero's maneuverability. Although the Mitsubishi A6M was outdated by 1944, design delays and production difficulties of newer Japanese aircraft types meant that it continued to serve in a front line role until the end of the war. During the final years of the War in the Pacific, the Zero was also adapted for use in kamikaze operations. During the course of the war, Japan produced more Zeros than any other model of combat aircraft.

The Mitsubishi A5M fighter was just entering service in early 1937, when the Imperial Japanese Navy 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 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 Imperial Japanese Navy sent out updated requirements in October calling for a speed of 600 km/h (370 mph) and a climb to 3,000 m (9,800 ft) in 3.5 min. With drop tanks, they 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 30 kg (66 lb) or 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 maneuverability 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 an aircraft carrier. All this was to be achieved with available engines, a significant design limitation.

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 could be 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 armor was provided for the pilot, engine or other critical points of the aircraft, and self-sealing fuel tanks, which were becoming common at the time, were not used. This made the Zero lighter, more maneuverable, and the longest range single engine fighter of WWII; which made it capable of searching out an enemy hundreds of kilometres (miles) away, bringing them to battle, then returning hundreds of kilometres back to its base or aircraft carrier. However, that trade in weight and construction also made it prone to catching fire and exploding when struck by enemy rounds.

With its low-wing cantilever monoplane layout, retractable, wide-set conventional landing gear and enclosed cockpit, the Zero was one of the most modern aircraft in the world at the time of its introduction. It had a fairly high-lift, low-speed wing with a 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 maneuverability, allowing it to out-turn any Allied fighter of the time. Early models were fitted with servo tabs on the ailerons after pilots complained 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 maneuvers.

It has been claimed that the Zero's design showed clear influence from American fighter aircraft and components exported to Japan in the 1930s, and in particular the Vought V-143 fighter. Chance Vought had sold the prototype for this aircraft and its plans to Japan in 1937. Eugene Wilson, President of Vought, claimed that when shown a captured Zero in 1943, he found that "There on the floor was the Vought V 142 or just the spitting image of it, Japanese-made," while the "power-plant installation was distinctly Chance Vought, the wheel stowage into the wing roots came from Northrop, and the Japanese designers had even copied the Navy inspection stamp from Pratt & Whitney type parts." While the sale of the V-143 was fully legal, Wilson later acknowledged the conflicts of interest that can arise whenever military technology is exported. Counterclaims maintain that there was no significant relationship between the V-143 (which was an unsuccessful design that had been rejected by the U.S. Army Air Corps and several export customers) and the Zero, with only a superficial similarity in layout. Allegations about the Zero being a copy have been mostly discredited.

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.

A6M2 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 currently 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. Reports of the Zero's performance filtered back to the US slowly. There they were dismissed by most military officials, who thought it was impossible for the Japanese to build such an aircraft.

A6M2 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

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 July 15, 1941.

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 back by 185 mm 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 carburetor 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 Type 99 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 sacrifed nearly 1,000 km (620 mi) of range. Nevertheless, the navy accepted the type and it entered production in April 1942.

The shorter wing span led to better roll, and the reduced drag allowed the diving speed to be increased to 670 km/h (420 mph). On the downside, turning and range, which were the strengths of the Model 21, suffered due to smaller ailerons, decreased lift and greater fuel consumption. The shorter range proved a significant limitation during the Solomons Campaign, during which Zeros based at Rabaul had to travel nearly to their maximum range to reach Guadalcanal and return. Consequently, the Model 32 was unsuited to that campaign and was used mainly for shorter range offensive missions and interception.

The appearance of the redesigned A6M3-32 prompted the US to assign the Model 32 a new code name, "Hap". This name was short-lived, as a protest from USAAF Commanding General Henry "Hap" Arnold forced a change to "Hamp". Soon after, it was realized that it was simply a new model of the "Zeke" and was termed "Zeke 32".

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 important, it regained back 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.

According to a theory, the very late production Model 22 might have had wings similar to the shortened, rounded-tip wing of the Model 52. One plane of such arrangement was photographed at Lakunai Airfield ("Rabaul East") in the second half of 1943, and has been published widely in a number of Japanese books. While the engine cowling is the same of previous Model 32 and 22, the theory proposes that the plane is an early production Model 52. However, the available evidence suggest that this "hybrid" type was simply an early production Model 52.

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.

A6M5 Type 0 Model 52

Sometimes considered as the most effective variant, the Model 52 was developed to again shorten the wings to increase speed and dispense with the folding wing mechanism. In addition, ailerons, aileron trim tab and flaps were revised. 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. The first Model 52 is said in the handling manual to have (seiz� bang�, or production number) 3904, which apparently refers to the prototype.

Research by Mr. Bunzo Komine published by Mr. Kenji Miyazaki states that aircraft 3904 through 4103 had the same exhaust system and cowl flaps as on the Model 22. This is partially corroborated by two wrecks researched by Mr. Stan Gajda and Mr. L. G. Halls, production number 4007 and 4043, respectively. (The upper cowling was slightly redesigned from that of the Model 22.)

A new exhaust system provided an increment of thrust by aiming the stacks aft and distributing them around the forward fuselage. The new exhaust system required "notched" cowl flaps and heat shields just aft of the stacks. (Note, however, that the handling manual translation states that the new style of exhaust commenced with number 3904. Whether this is correct, indicates retrofitting intentions, refers to the prototype but not to all subsequent planes, or is in error is not clear.) From production number 4274, the wing fuel tanks received carbon dioxide fire extinguishers. From number 4354, the radio became the Model 3, aerial Mark 1, and at that point it is said the antenna mast was shortened slightly. Through production number 4550, the lowest exhaust stacks were approximately the same length as those immediately above them. This caused hot exhaust to burn the forward edge of the landing gear doors and heat the tires. Therefore, from number 4551 Mitsubishi began to install shorter bottom stacks. Nakajima manufactured the Model 52 at its Koizumi plant in Gunma Prefecture. The A6M5 had a maximum speed of 565 km/h (351 mph)) at 6,000 m (20,000 ft) and reached that altitude in 7:01 minutes.

Subsequent variants included:

• A6M5a, Model 52 (K�, a) - 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. Hence, the bulge in the underside of the wing for each cannon's ammunition drum was deleted and the ejection port for spent cartridge cases was moved. Thicker wing skinning was installed to permit higher diving speeds.
• A6M5b, Model 52 (Otsu, b) - Armament change: The 7.7 mm (.303 in) Type 97 gun (750 m/s muzzle velocity and 600 m/1,970 ft range) in the right forward fuselage was replaced by a 13.2 mm Type 3 Browning-derived gun (790 m/s muzzle velocity and 900 m/2,950 ft range, with a rate of fire of 800 rounds per minute) with 240 rounds. The larger weapon required an enlarged opening, creating a distinctive asymmetric appearance to the top of the cowling, and a revised gas outlet near the windscreen. In addition, each wing cannon received a fairing at the wing leading edge. A plate of armored glass 45 mm thick was fitted to the windscreen. A larger propeller spinner was fitted, suggesting a change to the propeller. The type of ventral drop tank was changed, it now had fins and was suspended on a slanted pipe. The first of this variant was completed in April 1944 and it was produced until October 1944.
• A6M5c, Model 52 (Hei, c) - Armament change: One 13.2 mm (.51 in) Type 3 machine gun was added in each wing outboard of the cannon, and the 7.7 mm gun on the left side of the cowl was deleted. Four racks for rockets or small bombs were installed outboard of the 13 mm gun in each wing. Engine change: Some sources state that the hei had a Sakae 31 engine In addition, a 55 mm thick piece of armored glass was installed at the headrest and a plate of armor was installed behind the seat. The mounting of the central 300L drop tank changed to a four-post design. Wing skin was thickened further. The first of this variant was completed in September 1944. Because of the gain in weight, this variant was used mainly for intercepting B-29s and special attack.
• A6M5-S (A6M5 Yakan Sent�ki) - Armament change: To intercept B-29s and other night-flying aircraft, an air arsenal converted some Model 52s to night fighters. They were armed with one 20 mm Type 99 cannon behind the pilot, aimed upward, similar in intent to the Luftwaffe's Schr�ge Musik installation. However, lack of radar prevented them from being very effective.

Some Model 21 and 52 aircraft were converted to "bakusen" (fighter-bombers) by mounting a bomb rack and 250 kg bomb in place of the centerline drop tank.

Perhaps seven Model 52 planes were ostensibly converted into A6M5-K two-seat trainers. Mass production was contemplated by Hitachi, but not undertaken.