Mitsubishi A6M Zero A6M5 Tipo 0 Modelo 52

By 1943 the Zero's edge was fading. The P-38 Lightning, F6F Hellcat and F4U Corsair outclassed the A6M in speed, protection and firepower, and the intended successor, the A7M Reppu, was nowhere near ready. The Japanese Navy asked for an improved version as a stopgap. Mitsubishi produced it in June 1943 by modifying an A6M3; the provisional designation was "Model 22 Kai" (modified 22). The wing was shortened again to the 11.0 m of the Model 32, but this time with rounded tips and no folding mechanism, and the ailerons, trim tab and flaps were revised. The prototype flew in August 1943, and that same month a Navy Ministry order adopted it as the Zero Model 52. Sources differ on the detail: the technical table of the Japanese Wikipedia dates completion of the prototype to April 1943, whereas English-language sources speak of the conversion in June and a first flight in August.

The most recognisable external feature of the Model 52 is its exhaust system: instead of a common collector ring, each cylinder discharges through its own rearward-facing stack distributed around the forward fuselage, so that the exhaust jet adds thrust. The new stacks required notched cowl flaps and heat shields behind each pipe. The effect was substantial: with the same Sakae 21 as the Model 32 and nearly 200 kg more loaded weight, the 52 gained about 20 km/h and climbed better. The very first aircraft, however, still left the factory with the Model 22 collector and cowl flaps: research by Bunzo Komine, published by Kenji Miyazaki, places that arrangement on production numbers 3904 to 4103, partly corroborated by two wrecks numbered 4007 and 4043. According to the handling manual, 3904 was the first Model 52, probably the prototype itself. The system also had a drawback: the lower stacks, the same length as those above them up to aircraft 4550, scorched the landing-gear doors and heated the tyres, so from 4551 Mitsubishi fitted shorter bottom stacks and added protective plates.

The Model 52 evolved as production went on. From number 4274 the wing tanks received automatic carbon dioxide fire extinguishers, the first serious protective measure on a fighter that had made lightness its trademark; the lessons study of Operation I-Gō in April 1943 had already admitted that most losses were due to fire and that preventing it would multiply combat capability. From 4354 the radio became the Type 3 Kū-1 set, with a slightly shorter antenna mast. Wing skinning was thickened compared with earlier models, raising the diving limit. Production began at Mitsubishi in August 1943 and Nakajima took it up as well, at its Koizumi plant in Gunma Prefecture, from December 1943; most Model 52s actually came from Nakajima.

With 1,130 hp for take-off, the Model 52 reached 565 km/h at 6,000 m and climbed to that altitude in 7 minutes 1 second; service ceiling was 11,740 m and the diving limit 666.7 km/h. It was 9.121 m long and 3.57 m high, with a wing area of 21.30 m²; empty weight was 1,876 kg and normal loaded weight 2,607 kg according to the Nozawa compilation (3,007 kg overloaded), or 2,733 kg according to the variants table. With 60 L in the fuselage and 430 L in the wings the normal range was 1,921 km, and with a 320 L ventral tank and the wings at 520 L it reached 3,360 km. Armament was two 20 mm Type 99 Model 2 cannon with 100 rounds per gun and two 7.7 mm Type 97 machine guns with 700 rounds each, plus two 30 kg or 60 kg bombs.

From the 52 came the 52 Kō (belt-fed cannon), the 52 Otsu (13.2 mm machine gun and armoured windscreen) and the 52 Hei (three 13.2 mm guns, more armour and rocket rails), as well as conversions to night fighter with an oblique cannon, to fighter-bomber with a 250 kg bomb in place of the ventral tank, and to the two-seat A6M5-K trainer. Counting those subvariants, the 52 series was the most numerous of all Zeros, at about 6,000 aircraft. At the Battle of the Philippine Sea in June 1944 it equipped the front-line units; yet veterans such as Iyozō Fujita recalled that novices flew better in the nimble Model 21 and that in interception fights the ones shot down were often the veterans at the controls of the 52. After Leyte, the 52 became the archetypal kamikaze aircraft. Airframe 61-120 is today the only Zero flying with an original Sakae engine, and the A6M5 captured on Saipan and preserved at the National Air and Space Museum in Washington is one of the museum references for the variant.