Mitsubishi A6M Zero (1939)

Popularly known as the ‘Zero’, the Mitsubishi A6M was the world’s most capable carrier-based fighter at the time of its appearance, out-performing all land-based contemporaries. Latterly outclassed, it remained in service until the end of the war. This A6M2 was on strength with the 2nd Sentai, 1st Koku Kentai and was operating from the carrier Hiryu during the Battle of Midway in June 1942. In the course of the battle, the IJN put up large formations of Zero fighters for protection, but these could not prevent the loss of four Japanese carriers by the U.S. Pacific Fleet.

The brainchild of prolific designer Jiro Horikoshi, the Mitsubishi A6M (Allied reporting name ‘Zeke’) was schemed as a replacement for the same company’s A5M carrier fighter. A cantilever low-wing monoplane, the A6M1 prototype completed its maiden flight in April 1939 and in this form was powered by a Mitsubishi Zuisei 13 radial engine. In production form, the A6M2 of early 1940 introduced a new Nakajima Sakae 12 powerplant and was armed with a pair of wing-mounted 20mm (0.79in) cannon, plus two machine guns in the nose. The new engine was a result of early testing, in which the A6M1 had demonstrated excellent performance with the exception of maximum speed, which had failed to meet the original specification.

The Japanese attack on Rabaul in January 1942 was typical of the whirlwind successes in which the A6M was pitched in the initial phase of the war in the Pacific. Air power on Rabaul, the key strategic base on the island of New Britain, was provided by Australian Hudson light bombers and Wirraway reconnaissance aircraft, but there was no genuine fighter cover. On 20 January, a force of 120 A6M2s, Aichi D3A1s and Nakajima B5Ns took off from the carriers Zuikaku, Shokaku, Kaga and Akagi, attacking installations at Rabaul. Slicing through gallant opposition put up by the Wirraways, the IJN aircraft paved the way for a task force of 5300 men that landed at Simpson Harbour on 23 January, securing the port and the airfield at Kavieng. After capturing Rabaul, Japan established a major base and proceeded to land on mainland New Guinea, advancing towards Port Moresby and Australia.

As early as 1937 the Imperial Japanese Navy began searching for a craft to replace its A5M carrier-based fighters. That year it issued specifications so stringent that only Mitsubishi was willing to hazard a design. Specifically, the navy wanted a fighter of prodigious range and maneuverability, one able to defeat bigger land-based opponents. A design team headed by Jiro Horikoshi originated a prototype in 1939. The A6M was a study in aerodynamic cleanliness despite its bulky radial engine. It had widetrack undercarriage for easy landing and was heavily armed with two cannons and two machine guns. Tests proved it possessed phenomenal climbing and turning ability, so it entered production in 1940, the Japanese year 5700. Henceforth, the new fighter was known officially as the Type 0, but it passed into history as the Reisen, or Zero.

A small production batch of 30 Zeroes was sent to China in the summer of 1940 for evaluation, and they literally swept the sky of Chinese opposition. The official military designation for the new warplane was Navy Type 0 Carrier Fighter and in 1940 initial combat trials were undertaken in China by a preproduction batch. The antiquated Polikarpov fighters flown by the Chinese proved to be no match for the Zero. It was in the course of these operational trials that the Zero recorded its first aerial victory, in September 1940. By the end of that year, the Zero detachment had claimed 59 victories without loss.

Such prowess was duly noted by Claire L. Chennault, future commander of the famed Flying Tigers, but his warnings were ignored. Zeroes subsequently spearheaded the Japanese attack on Pearl Harbor in December 1941, and over the next six months they ran roughshod over all Allied opposition.

Once entering combat in World War II, the highly agile A6M2 proved itself an immediate success, quickly gaining aerial supremacy during the Imperial Japanese Navy’s campaigns in the East Indies and Southeast Asia. The A6M2 was the IJN’s premier fighter during the raid on Pearl Harbor in December 1941, in which eight Zero fighters were lost from a total of 105 involved in the surprise attack on the U.S. Navy fleet. The A6M remained the service’s pre-eminent fighter in theatre as fighting extended to Malaya, the Philippines and Burma. Along the way, it demonstrated its superiority against lesser Allied types in theatre, including the Brewster Buffalo, Curtiss P-36 and P-40 and Hawker Hurricane fighters. Japan’s leading ace of the Pacific war, Saburo Sakai, flew a Zero, who is believed to have achieved 64 aerial kills.

An improved A6M3 entered service in spring 1942, now powered by a Sakae 21 with two-stage supercharger. Not only supremely manoeuvrable, the Zero was also well equipped for fighting at the extended ranges encountered in the Pacific theatre. The aircraft could carry a fuel tank under the fuselage to increase the endurance of its long-range fighter patrols. Even before the arrival of the powerful Hellcat, however, the A6M had begun to suffer at the hands of the Grumman F4F Wildcat, which, although inferior in terms of performance and agility, was better able to withstand battle damage and possessed heavier-hitting armament, self-sealing tanks and armour protection for the pilot. While the Zero was always fast, it was also underpowered, and as a result the design stressed lightweight construction. This, in turn, led to a fighter that was vulnerable to even machine gun fire, and had little in the way of armour protection.

However, following the Japanese defeat at Midway in June 1942, the fabled fighter lost much of its ascendancy to new Allied fighters and a growing shortage of experienced pilots. New and more powerful versions of the Zero were introduced to stem the tide, but relatively weak construction could not withstand mounting Allied firepower. Furthermore, the additional weight of new weapons and equipment eroded its famous powers of maneuver.

Changing Fortunes

The Battle of Midway of June 1942 represented a watershed for the Zero, and thereafter the Japanese fighter began to be increasingly outclassed by U.S. opposition, in particular the U.S. Navy’s Grumman F6F Hellcat, which proved to be faster than the Zero at all altitudes. While the A6M3 version had helped to offset the appearance of the Wildcat, it could do little in the face of the Hellcat.

In an effort to wring additional performance out of the basic airframe, the IJN introduced the A6M5, with Sakae 21 and an improved exhaust system. This version was actually slower than the A6M2, but enjoyed a superior rate of climb and was faster in the dive. It was also built in greater numbers than any of the other Zero models. As the tide of the war turned against the Japanese, the Zero was also used for kamikaze raids, and in one action, five A6M5s sunk the U.S. Navy carrier St Lo and damaged three others in October 1944.

The last models in the Zero line comprised the A6M6 of late 1944, with a water-methanol boosted Sakae 31, and the A6M7 fighter/dive-bomber of mid-1945 with a rack under the fuselage for the carriage of a single 250kg (551lb) bomb. In total, in excess of 10,000 Zero fighters were completed, including a floatplane version built by Nakajima as the A6M2N (Allied reporting name ‘Rufe’). As such, it was the most prolific Japanese fighter of all time.

Although the A6M’s vulnerability to the Hellcat in particular was clear by the time of the Battles of the Philippines and Leyte Gulf in 1944, the lack of an adequate replacement meant the Zero was forced to soldier on in IJN service until the bitter end.

By 1945 most A6Ms had been converted into kamikazes in a futile attempt to halt the Allied surge toward the homeland. A total of 10,964 were constructed.

The legendary A6M (the dreaded Zero) was the first carrier-based fighter in history to outperform land-based equivalents, and it arrived in greater quantities than any other Japanese aircraft. Despite the Zero’s aura of invincibility, better Allied machines gradually rendered it obsolete.

A6M5c Type 0 Model 52

Considered the most effective variant, the Model 52 was developed to face the powerful American Hellcat and Corsair, superior mostly for engine power and armament. The variant was a modest update of the A6M3 Model 22, with non-folding wing tips and thicker wing skinning to permit faster diving speeds, plus an improved exhaust system. The latter used four ejector exhaust stacks, providing an increment of thrust, projecting along each side of the forward fuselage. The new exhaust system required modified “notched” cowl flaps and small rectangular plates which were riveted to the fuselage, just aft of the exhausts. Two smaller exhaust stacks exited via small cowling flaps immediately forward of and just below each of the wing leading edges. The improved roll-rate of the clipped-wing A6M3 was now built in.

Sub-variants included:

* “A6M5a Model 52a «Kou»,” featuring Type 99-II cannon with belt feed of the Mk 4 instead of drum feed Mk 3 (100 rpg), permitting a bigger ammunition supply (125 rpg)

* “A6M5b Model 52b «Otsu»,” with an armor glass windscreen, a fuel tank fire extinguisher and the 7.7 mm (.303 in) Type 97 gun (750 m/s muzzle velocity and 600 m/1,970 ft range) in the left forward fuselage was replaced by a 13.2 mm/.51 in Type 3 Browning-derived gun (790 m/s muzzle velocity and 900 m/2,950 ft range) with 240 rounds. The larger weapon required an enlarged cowling opening, creating a distinctive asymmetric appearance to the top of the cowling.

* “A6M5c Model 52c «Hei»” with more armor plate on the cabin’s windshield (5.5 cm/2.2 in) and behind the pilot’s seat. The wing skinning was further thickened in localised areas to allow for a further increase in dive speed. This version also had a modified armament fit of three 13.2 mm (.51 in) guns (one in the forward fuselage, and one in each wing with a rate of fire of 800 rpm), twin 20 mm Type 99-II guns and an additional fuel tank with a capacity of 367 L (97 US gal), often replaced by a 250 kg bomb.

The A6M5 had a maximum speed of 540 km/h (340 mph) and reached a height of 8,000 m (26,250 ft) in nine minutes, 57 seconds. Other variants were the night fighter A6M5d-S (modified for night combat, armed with one 20 mm Type 99 cannon, inclined back to the pilot’s cockpit) and A6M5-K “Zero-Reisen”(model l22) tandem trainer version, also manufactured by Mitsubishi.

Early War Japanese Air Supremacy – the “Zero”

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