Designation:
A: carrier fighter (capable of flying off an aircraft carrier)
6: the sixth carrier fighter ordered
M: Mitsubishi
52: model variant
A6M1
Special attention was paid to weight savings, and a new special aluminium alloy developed by Sumimoto was adopted. Powered by a Mitsubishi Zuisei 13 (Auspicious Star) fourteen-cylinder, twin-row air-cooled radial engine, rated at 780 hp for take off and 875 hp at 11,810 feet.
Two 7.7 mm Type 97 machine guns in the upper fuselage decking
Two wing-mounted 20-mm Type 99 cannon
Three-bladed constant speed propeller
Speed was 305 mph at 12,470 feet – slightly below requirement
A6M2
Re-engineered with a Nakajima NK1C Sakae 12 (Prosperity) engine
Manually upward-folding wingtips (about 20 inches long) were incorporated so that the plane could fit the deck elevators of the Imperial Navy’s aircraft carriers. This modification resulted in a change of designation to Navy Type 0 Carrier Fighter Model 21.
During the first year of the Pacific War, the standard shipboard fighter serving with the US Navy was the Grumman F4F Wildcat. The A6M2 was superior to the F4F Wildcat in speed, climb rate, and maneuverability, but the Wildcat had better firepower and was more robust. In a dive the two aircraft were fairly equal, but the turning circle of the Zero Fighter was very much smaller than that of the Wildcat by virtue of its lower wing loadings.
A6M2-N “Rufe”
A seaplane adaptation of the Mitsubishi A6M2 Zero Fighter
The A6M2 Model 11 with the non-folding wingtips was used as the basis.
The retractable landing gear was removed and the wheel wells were faired over. A large central float was mounted and two stabilizing cantilever floats were fitted underneath the outboard wings.
A6M3”Hap”
Powered by a 1130 hp Sakae 21 equipped with a two-speed supercharger instead of a single-speed unit as used on the earlier Sakae 12.
The ammunition supply for the wing-mounted 20-mm cannon was increased from 60 rpg to 100 rpg. In order to simplify production and maintenance, the folding wingtips and the tab balances were removed, reducing the wingspan to 36 feet 1 1/16 inches and wing area to 231.75 square feet. This resulted in a slight increase in the level speed with little adverse effect in the overall maneuverability. Japanese pilots did find that both the maneuverability and climb rate of the new clipped-wing Zero Fighter were slightly poorer than those of the earlier A6M2, but the aircraft was considerably faster in a dive, the ailerons were more effective, and the roll rate was better at high speed.
A6M4
Modified to take an experimental turbo supercharged Sakae engine. However, major teething troubles were encountered with the A6M4, and no production order was placed.
A6M5
The converted A6M3 aircraft was fitted with a new set of wings with heavier gauge skin and with redesigned, non-folding rounded wingtips. The wingspan was reduced to 36 feet 1 1/16 inches
The A6M5 was faster than the A6M3 Model 32. More important, it could now be dived at speeds of up to 410 mph. It was rushed into production as the Navy Type 0 Carrier Fighter Model 52.
The Model 52 began to reach front line units in the autumn of 1943. It was immediately confronted by the new Grumman F6F Hellcat, which was slightly less maneuverable but which was much more strongly built, heavier armed, and better protected.
A6M5a
Heavier gauge wing skin which enabled a further increase in diving speed to 460 mph, bringing it almost up to Western standards. This was to be the highest diving speed attained by any Zero variant. Armament was improved by replacing the drum fed Type 99 Model 2 Mk3 cannon with 100 rpg with belt-fed 20-mm Type 99 Model 2 Mk4 cannon with 125 rpg.
A6M5b
Additional armament, some fire protection for the fuel tanks and some armor protection for the pilot. One of the fuselage-mounted 7.7-mm Type 97 machine guns was replaced by a 13.2-mm Type 3 machine gun.
A6M5c
Two additional 13.2-mm machine guns were installed in the wings outboard of the cannon. The fuselage-mounted 13.2-mm machine gun was retained, but the smaller-caliber 7.7-mm fuselage-mounted gun was deleted. An armor plate was mounted behind the pilot’s seat to provide some protection against attacks from the rear. Wing racks were provided for unguided air-to-air rockets.
A6M6c
Powered by the water-methanol boosted Sakae 31 engine
A6M7 dive bomber
The under-fuselage drop tank installation was replaced by a special bomb rack capable of carrying a single 551 pound or 1100 pound bomb.
A6M8
The A6M8 was the last production version of the Zero.
The forward fuselage was completely redesigned to accommodate the 1560 hp Mitsubishi MK8P Kinsei 62, which had a larger diameter than the Sakae, requiring that the fuselage-mounted gun be removed. At the same time, the fuel tank fire-extinguishing system was improved, and additional fuel tankage was added. The fuselage center line could carry a single 1100-lb bomb, and a pair of 77-Imp gall drop tanks could be carried underneath the wings.
Six thousand three hundred machines were ordered. However, owing to the chaotic conditions prevailing in Japanese industry in the closing months of the war, none were actually delivered.
Source: https://www.fighter-planes.com/info/a6m.htm