A6M3 "Hap"

In mid-1941, work began on a new version of the Zero Fighter, the A6M3 powered by a 1130 hp Sakae 21. This engine was equipped with a two-speed supercharger instead of a single-speed unit as used on the earlier Sakae 12. The new engine required that the firewall be moved 8 inches further aft, which reduced the fuselage fuel capacity from 21.6 Imp gall to 13.2 Imp gall. The shape of the engine cowling had to be changed in order to incorporate the supercharger air intake in its upper lip.

The first A6M3 flew in June of 1941. Although the aircraft performed satisfactorily, the flight trials of the A6M3 were somewhat disappointing since performance figures fell below the calculated values. In addition, production had to be delayed until sufficient numbers of Sakae 21 engines became available.

The type was placed in production as the Navy Type 0 Carrier Fighter Model 32. Beginning with the fourth aircraft, the ammunition supply for the wing-mounted 20-mm cannon was increased from 60 rpg to 100 rpg. Soon thereafter, 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.

343 A6M3s were built by Mitsubishi, with an unspecified number also being built by Nakajima at Koizumi.

Following limited service in Japan, the A6M3s were deployed to the New Guinea/Solomons area in the late spring of 1942 in preparation for the invasion of Australia. Initially, the Allies thought that the A6M3 was an entirely new fighter because of its squared-off wingtips, and Capt. Frank McCoy's team at the Directorate of Intelligence of the Allied Air Forces, Southwest Pacific Area, assigned it the code name HAP, after the nickname of General Henry Arnold, the USAAF's Chief of Staff. The General was not amused, and had Capt. McCoy called onto the carpet to explain just what he was up to. Capt McCoy seems to have survived this particular episode, but the code name of the new square-winged fighter was quietly changed to HAMP. When Allied intelligence finally recognized that the aircraft was not a new design but was actually a modified version of the ZEKE, it was renamed ZEKE 32.

Following the American landing at Guadalcanal, the A6M3 were forced to operate from bases 560 nautical miles away from the landing force. During this operation, a large number of A6M3s were lost because they had insufficient range. The Sakae 21 engine of the A6M3 had a higher fuel consumption rate than the Sakae 12, and this, acting in concert with the reduced fuel capacity resulting from the installation of the two-speed supercharger, had an adverse effect on range, which had been one of the strong points of the A6M2. In order to increase the range, a 9.9 Imp gall fuel tank was fitted in each wing outboard of the cannon. The folding wingtips were restored. This new version was still known under the short designation A6M3, but bore the new designation of Navy Type 0 Carrier Fighter Model 22. It could be externally distinguished from earlier A6M3 models by the rounded-off wingtips. The aircraft was known as the Navy Type 0 Carrier Fighter Model 22A when long-barreled 20-mm Type 99 Model 2 Mk 3 cannon were installed. The rounded-wingtip Model 22 became the prime carrier fighter of the A6M3 series, some 560 being built by Mitsubishi.

Specification of A6M3 Navy Type 0 Carrier Fighter Model 32:

One Nakajima NK1F Sakae 21 fourteen cylinder air-cooled radial, rated at 1130 hp for takeoff, 1100 hp at 9350 feet, 980 hp at 19,685 feet.

Performance: Maximum speed 338 mph at 19,685 feet. Cruising speed 230 mph. Initial climb rate 4500 feet per minute. Radius of turn with entry speed at 230 mph was 1118 feet. Entering a 180 degree steep turn with an entry speed of 230 mph, the fighter could complete

the turn in 6.02 seconds, with an exit speed from the turn of 189 mph. At slower speed, the radius of turn was 629 feet. Climb to 19,685 feet in 7 minutes 19 seconds. Service ceiling 36,250 feet. Maximum range 1477 miles.

Dimensions: Wingspan 36 feet 1 1/16 inches, length 29 feet 8 11/16 inches, height 11 feet 6 5/32 inches, wing area 231.75 square feet. Weights: 3984 pounds empty, 5609 pounds loaded.

Armament: Two 7.7-mm Type 97 machine guns in the upper fuselage decking and two 20-mm Type 99 cannon in the wings. A 72.6-Imp gall drop tank could be carried underneath the fuselage.