A6M "Zero", Japanese Carrier Fighter

Mitsubishi A6M2 Reisen "Zero" or "Zeke"

Specifications:

The legendary Zero was the terror of the Pacific for the first year or so of the war. Accepted by the Navy in July 1940, it was just coming into mass production in 1941, and the available Zeros (roughly 400 in number) were assigned to 1 Air Fleet for the Pearl Harbor raid and to Tainan Air Group to cover the Philippines invasion. Its range and low-speed maneuverability were phenomenal, and it was faster and had a better climb rate and service ceiling than most first-generation Allied fighters. Flown by superbly trained pilots, the Zero quickly acquired an aura of invincibility in the eyes of Allied airmen.

The aircraft was designed in response to a very demanding set of requirements published by the Naval Aviation Department in the spring of 1937. It needed the performance and firepower to be an effective interceptor, the maneuverability to engage enemy fighters, and the range to escort the G3M "Nell" on long missions. To meet these conflicting requirements, the Mitsubishi design team, led by Horikoshi Jirō, deliberately reduced the safety factors on many structural components and made use of the new "Super Ultra Duralumin", an aluminum-zinc alloy with remarkable strength. Every effort was made to reduce drag, by using flush riveting, retractable landing gear, a full canopy, and a "washout" wing tip configuration.

Other notable features of the design included unusually large ailerons and an integral wing. The wing was a single unit, divided into left and right fuel tanks whose large volume gave the aircraft its remarkable range. The upper surface of the center of the wing  was the floor of the cockpit. This integral design contributed structural strength and made the aircraft easy to assemble and disassemble. Its low wing loading gave it the smallest turn radius of any aircraft then in production, and its large ailerons gave it an excellent roll rate. It was one of the first aircraft to be equipped with a drop tank.

Although the Zero first saw combat over Chungking on 19 August 1940, production was initially slow. Some of the internal opposition to the Pearl Harbor operation was based on the fear that only 150 of the aircraft would be available by October 1941, which was not enough for both Tainan Air Group and 1 Air Fleet. One bottleneck was the limited availability of 20mm cannon, and some of the early training was conducted with Zeros armed with only a single 20mm cannon.

Considerable information on the Zero was available to the Allies well before war broke out in the Pacific. Claire Chennault had studied the fighter in China, filed a report with Marshall in December 1940 that was passed on to Short at Oahu, and in July 1941 Chennault lectured a spellbound audience of Hawaiian Air Force pilots for three hours on the flight characteristics of the new Japanese fighter. Lieutenant Stephen Jurika, an assistant naval attaché, actually managed to get into the cockpit of a Zero on exhibition in Tokyo and later filed a detailed report with the Office of Naval Intelligence. However, the reports seem not to have been widely believed.

Disheartened survivors of combat with Zeros reported that the aircraft engaged in elaborate acrobatics in the middle of dogfights, as if taunting the Allied fliers. These acrobatics may actually have been a means of communication or, more likely, the unorthodox hineri-komi combat maneuver taught to Imperial Navy pilots. Or they could have been exactly what the Allied pilots thought they were. Bergerud quotes Jack Fletcher:

... at that time the Japanese Zeroes all wore Seven League Boots and our aviators gave them a lot of ... respect.

However, the Zero had a number of weaknesses that became evident only after several months of combat. It was fragile, with several single-point failure points where one hit could destroy the entire aircraft. It lacked self-sealing fuel tanks, making it a firetrap. As one American flier observed, it was easily destroyed once you had it in your sights; the trick was getting it into your sights.

Other weaknesses were discovered after the Allies captured an intact Zero in the Aleutians in the summer of 1942 and performed extensive flight testing. It was found that the Zero could not maintain a steep dive, and it lost maneuverability at speeds over 260 mph (418 km/h) or at altitudes above 15,000 feet (4600m). The Zero’s large propeller generated high torque, so that its roll rate was much slower to the right than the left. Allied pilots were instructed that they could shake a Zero off their tail with a split-S to the right. Likewise, the recommended attack procedure was a diving attack followed by a sharp turn to the right. The U.S. Navy developed cooperative tactics such as the Thatch Weave that took advantage of the better radio communications gear carried by Allied fighters. (The Zero was equipped with a very poor radio telephone, the Type 96, that was often removed by its pilots to save weight.)

Horikoshi believed that the greatest flaw in his design was its use of a relatively low-power aircraft engine, the 950hp (708 kW) Nakajima Sakae. But this could not be helped. Japan's limited access to alloying metals caused a shortage of the high-tensile steel used in more powerful American aircraft engines, and in any case a larger engine would simply have torn the fragile Zero apart.

The Zero’s armament was better on paper than in practice. Although the 20mm cannon shells packed a lot of punch, the guns had a rather low muzzle velocity, reducing their accuracy. They also had a rather low rate of fire. Perhaps this was just as well, given the ammunition load of just 60 rounds per gun. Bergerud quotes Sakai Saburo, the second highest scoring Japanese ace to survive the war:

Our 20mm cannons were big, heavy and slow firing. It was extremely hard to hit a moving target. Shooting down an enemy aircraft was like hitting a dragonfly with a rifle! It was never easy to score ... our opponents were tough.

Another veteran, Fujita Iyozō, believed that an inexperienced pilot could get just two bursts out the 20mm cannon before running out of ammunition, while more experienced pilots could get five or six bursts.

The 0.303 machine guns in the engine cowling were often ineffective against sturdy Allied aircraft.  The Zero had an ammunition select switch that permitted its pilots to find the range with the 0.303s, then switching on the cannon to make the kill. However, this was problematic, because the 0.303 rounds and the 20mm rounds had very different ballistics. The Japanese quickly became aware of the weakness of the original armament, and the A6M3 used a more powerful 20mm cannon whose ballistics better matched those of the 0.303 machine guns. Later models (beginning with late production versions of the A6M5) increased the 20mm ammunition loadout and replaced the light machine guns with more effective heavy machine guns.

Operational units improvised a bomb rack for the Zero that allowed it to carry a 250 kg bomb in place of the drop tank. This fighter-bomber concept was taken up by the manufacturer as the A6M7, which had a center bomb rack and fittings for two drop tanks outboard of the wing armament.

The Zero remained in production throughout the war, and was produced in greater numbers than any other Japanese fighter. However, the Zero was not a match for second-generation Allied fighters, such as the Hellcat, in spite of various design refinements. The replacement A7M Reppu "Sam" suffered from the same flawed design philosophy as the Zero and experienced repeated production delays that prevented it from ever entering combat. By mid-1944 the Japanese were experimenting with skip bombing using Zeroes armed with 250 kg (551 lb) bombs, but the experiments were abandoned in favor of kamikaze attack.

The Zero required an overhaul every 150 hours of flight time, but the Japanese often stretched this to 200 hours or more, with unhappy results.

The official Allied code name for this fighter was "Zeke," but Allied pilots usually referred to it as the "Zero," which was the Japanese name for the aircraft (Reisen). However, there was some tendency for Allied soldiers, sailors, and airmen to call any single-seat radial-engine Japanese monoplane aircraft a "Zero."

Zero recognition training film

Photo Gallery

NARA	U.S. Navy	NMUSAF	U.S. Navy	U.S. Navy
Wikimedia Commons	Wikimedia Commons	U.S. Army	U.S. Army	NMUSAF

References

Bergerud (2000)

Francillon (1979)

Inoguchi, Nakajima, and Pineau (1958)

Okumiya et al. (1956)
Peattie (2001)

Peattie et al. (2011)

Prange (1982)

Sakai et al. (1957)

Werneth (2008)

Wilson (1998)

Zimm (2011)

The Pacific War Online Encyclopedia © 2007-2009, 2013-2015 by Kent G. Budge. Index

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