Mitsubishi A6M Zero A6M5c Modelo 52 Hei

The A6M5c, known to the Imperial Japanese Navy as the Type 0 Carrier Fighter Model 52 Hei (零戦五二丙型), was the third and heaviest sub-variant of the Model 52 and the last Zero built in large numbers. It was born of the emergency that followed the Battle of the Philippine Sea in June 1944: Japanese naval aviation had been cut to pieces by the Grumman F6F Hellcat, and the fighter meant to replace the Zero, the Mitsubishi J2M Raiden, was still not reaching series production. With no alternative in hand, the Navy ordered yet another squeeze of an airframe it already regarded as obsolete, this time betting on firepower and pilot protection rather than the lightness that had defined the aircraft.

The most visible change was the armament. The surviving 7.7 mm Type 97 machine gun on the left side of the cowling was deleted, leaving in the fuselage only the 13.2 mm Type 3 gun introduced on the Model 52 Otsu. Two further Type 3 guns were added, one in each wing outboard of the 20 mm Type 99 cannon, each firing at 800 rounds per minute. The combination of three 13.2 mm guns and two 20 mm cannon made the Hei the best-armed Zero ever to reach the units, and outboard of the new machine guns each wing received four rails for air-to-air rockets or light bombs, intended above all for attacks on bomber formations.

Protection received attention unprecedented in the series. A 55 mm slab of armoured glass was fitted behind the headrest and an 8 mm steel plate behind the seat; the centre fuel tank became self-sealing and the wing skinning was thickened further, with local reinforcement that allowed higher diving speeds. The mounting of the 300-litre ventral drop tank changed to a four-post design. The first example of the sub-variant was completed in September 1944.

The engine was the problem. All these improvements were piled onto the same 1,130 hp Nakajima Sakae 21 that had powered the Model 52 since 1943. Mitsubishi's engineers had asked for the larger and more powerful Mitsubishi Kinsei to offset the predictable growth in weight, but the Navy refused once again and insisted on keeping the Sakae 21 until the water-methanol-injected Sakae 31 became available. Acceptance testing of that engine was interrupted in the autumn of 1944, when the naval inspectors had to turn to fixing a weakness in the Sakae 21's reduction gear on some 300 Model 52-series Zeros, and with the Philippines campaign under way the Hei went into mass production with the old engine. The outcome, as Japanese historiography describes it, was an aircraft whose loaded weight approached 3,000 kg, which gained in diving speed but lost at once the manoeuvrability and climb that had been the Zero's hallmarks. Western literature records that some sources credit this sub-variant with the Sakae 31, but Japanese records and the standard technical references assign that engine to the A6M6c and A6M7, not to the Hei.

Because of that burden the Model 52 Hei was used mainly in two roles: intercepting Boeing B-29s over the home islands and special attack. Well-known photographs show A6M5cs preparing for kamikaze sorties in Kyushu in early 1945, and the Fuyō night-fighter unit under Tadashi Minobe was issued these "heavily armed and armoured" machines even though it lacked any real night-fighting equipment. The Hei nevertheless fought in the air to the very end: on 3 August 1945 Lieutenant Hiroshi Morioka, an ace of the 302nd Kōkūtai who flew with a prosthetic left hand, led a section of four Zeros from the cockpit of a 52 Hei and shot down a P-51 Mustang over Sagami Bay, and on 15 August, the morning of the surrender itself, the Zeros of the 302nd and 252nd Kōkūtai fought their last action against Allied carrier aircraft.

Production was shared between Mitsubishi and Nakajima, the latter also building the sub-variant alongside the later Model 62; sources differ widely on the total, and the figure of 93 aircraft given in French literature sits awkwardly beside the "mass-produced" of the Japanese record. Some remains survive: the Chiran Peace Museum for Kamikaze Pilots displays, essentially as raised from the sea in 1980, the forward section of 52 Hei ヨD-127 (Nakajima c/n 62343), lost in May 1945 off Koshiki Island, and a Hei fuselage recovered from Kinkō Bay was used to rebuild the Model 52 Ko displayed at Kanoya air base. In design terms the A6M5c was also the direct foundation of the Zero's final line: from the Hei came the A6M6c Model 53 prototype with the Sakae 31, the A6M7 Model 62/63 attack variant with identical armament, and the first prototype of the Kinsei-engined A6M8 Model 54.