- A6M5 Type 0 Model 52: This variant, which is regarded as the most effective one, was developed to make wings shorter, in order to increase speed and dispense with the folding wing mechanism. Additionally, ailerons, aileron trim tabs and flaps were also revised. The early machines were manufactured by Mitsubishi but production was soon overtook by Nakajima and a total of 747 aircraft were made.
The prototype was completed in June 1943 by modifying an A6M3 and flew for the first time in August that same year.
The A6M5 featured a new exhaust system which required cowl flaps to be "notched" and heat shields just aft of the stacks. Apparently, early machines differed from the rest of the series in having the same exhaust system as the A6M3 Model 22, however, from a batch onwards, the machines were standardised and they even received carbon dioxide fire extinguishers in the wing fuel tanks. Later on an improved radio was added which required the antenna mast to be slightly shortened. The new arrangement of the exhaust system expelled the heat just under the wing, causing burns on the forward edge of the landing gear doors and heated the tires. Shorter bottom stacks were installed to prevent this. The A6M5 had a maximum speed of 565 km/h (351 mph) at 6.000 m (20.000 ft) high and could reach that altitude in 7.01 minutes.
Many sub-variants were manufactured: - A6M5a Model 52: This variant had its Type 99-2 Mark 3 cannon replaced with a Type 99-2 Mark 4. As those weapons had different ammo feeding system, the bulge created underwing for the ammunition drum was deleted and the ejection port for spent cartridges was moved. Thicker wing skinning was added too to allow higher diving speeds. A total of 391 machines of this sub-variant were manufactured by both Mitsubishi and Nakajima from July 1943 until March 1944.
- A6M5b Model 52: This featured heavier armament as its 7.7 mm (0.303 in) Type 97 machine guns located in the right forward fuselage, was replaced by a 13.2 mm Type 3 Browning-derived machine gun. This larger gun required an enlarged opening creating a distinctive asymmetric appearance to the top of the cowling and a revised gas outlet near the windscreen, where a plate of armoured glass 45 mm (1.8 in) thick was also fitted. Additionally each wing cannon received a fairing at the leading wing edge. A large propeller spinner was also fitted which suggest a new propeller too. The ventral drop tank was also changed as now it had fins and was suspended on a slanted pipe. A total of 470 aircraft were completed from April 1944 (when the prototype was completed) until October 1944.
- A6M5c Model 52: This variant had one 13.2 mm (0.51 in) Type 3 machine gun added in each wing outboard of the cannon and the 7.7 mm machine gun on the left side of the cowl was deleted. Four racks for rockets or small bombs were installed at the outboard of the 13 mm cannon in each wing. It seems that this variant may had been powered by the Nakajima Sakae 31 radial engine. A thicker (55 mm/2.2 in) armoured glass panel was installed at the headrest and an 8 mm (0.31 in) thick plate of armour was placed behind the seat. The mounting of the central 300 L (79 US Gal) drop tank changed to a four-post design. Wing skin was thickened further. The first aircraft of this variant was completed in September 1944 and only 93 machines were completed before the end of the war. Given its extra weight, this variant was used to intercept B-29 bombers and special attack (kamikaze) missions.
- A6M5-S: In order to intercept the B-29 bombers and other night-flying aircraft, the 21st Naval Aviation Workshop at Omura, converted some few (7 machines in total) Model 52 into night-fighters. They were armed with one 20 mm Type 99 cannon placed behind the pilot which was aimed upwards copying the Luftwaffe's Schräge Musik arrangement. However, as they lacked radar, their effectiveness was very limited.
- A6M5-K: Seven machines of the Model 52 were rebuilt into two-seat trainers in February 1945 at the 21st Naval Aviation Workshop in Omura. It was estimated that Hitachi would start mass-producing them, but this didn't happen.
Additionally, some both A6M3 and A6M5 were converted to fighter-bombers by mounting a bomb rack and a 250 kg (550 lb) bomb instead of the central fuel tank. - A6M6 Type 0 Model 53: This variant was developed to be powered by the new Nakajima Sakae 31a engine, which featured water-methanol engine boost and self-sealing fuel tanks. Preliminary tests showed its performance to be unsatisfactory as the extra engine power didn't materialise and the fuel injection system proved to be unreliable. Apparently a single prototype was produced in December 1944 but the end of the war prevented further development.
- A6M7 Type 0 Model 62/63: This was the last variant to see service. It was designed as an answer to a requirement made by the Imperial Japanese Navy Air Service (IJNAS) for a dedicated attack/dive bomber that could operate from smaller aircraft carriers or, according to other sources, replace the obsolete Aichi D3A. This variant had considerable design changes like reinforced vertical stabiliser, a special bomb rack, provision for two 350 L (92 US Gal) drop tanks and the fixed bomb/rocket wing stoppers on the underside of the wings. It was also powered by a new powerplant. A Nakajima Sakae 31 radial engine which yielded 1.130 hp on take-off. Overall it had a general armament layout similar to the A6M5c with the exception of the central bomb rack which was capable of carrying 250 kg or 500 kg bombs.
An unknown number of aircraft of this variant were made in May 1945 by Mitsubishi and most of them were used in Kamikaze attacks. - A6M8 Type Model 64: This variant was similar to the A6M6 but with the Nakajima Sakae engine (which was now out of production) replaced by the Mitsubishi Kinsei 62 radial engine which delivered 1.560 hp of power. This resulted in a modified cowling and nose. Carburettor intake was longer, a long duct like the one of the Nakajima B6N was added and a large spinner, like the one present at the Yokosuka D4Y was mounted. It was armed with two 13.2 mm (0.52 in) Type 3 machine guns and two 20 mm (0.80 in) cannons in the wings. Additionally it was modified to carry two 150 L (40 US Gal) drop tanks on either wing in order to allow the mounting of a 250 Kg bomb under the fuselage. Two prototypes were completed in April 1945 (some sources claim the first one was completed in November 1944 and the second one in June 1945) but the chaotic situation of the Japanese industry during this period of the war prevented the mass-production of this variant of which more than 6.300 machines were expected to be manufactured. Eventually only the two prototypes were completed and flown.
Sources:
1. https://en.wikipedia.org/wiki/Mitsubishi_A6M_Zero
2. https://www.valka.cz/Micubisi-A6M7-63-Reisen-Zeke-Zero-t1281
3. https://www.valka.cz/Micubisi-A6M8-64-Reisen-Zeke-Zero-t27679
4. https://www.valka.cz/Micubisi-A6M6c-53c-Reisen-Zeke-Zero-t35110
5. https://www.valka.cz/Micubisi-A6M5-K-Zeke-Zero-t49190
6. https://www.valka.cz/Micubisi-A6M5a-52A-Reisen-Zeke-Zero-t86308
7. https://www.valka.cz/Micubisi-A6M5b-52B-Reisen-Zeke-Zero-t1280
8. https://www.valka.cz/Micubisi-A6M5c-52C-Reisen-Zeke-Zero-t27682
9. https://www.valka.cz/Micubisi-A6M5d-S-52D-Reisen-Zeke-Zero-t35347
10. Salamander Books - The Complete Book of Fighters
11. AJ Press - Monografie Lotnicze 7 - Mitsubishi A6M Zero (translated)
12. Signal Squadron - Aircraft in Action 59 - Mitsubishi A6M Zero in Action
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