|Japanese A6M5 Type 0 Model 52|
|Designed by||Jiro Horikoshi|
|First flight||1 April 1939|
The Mitsubishi A6M Zero was a long range fighter aircraft operated by the Imperial Japanese Navy Air Service (IJNAS) from 1940 to 1945. The A6M was usually referred to by the Allies as the "Zero"—a name that was frequently misapplied to other Japanese fighters, such as the Nakajima Ki-43—as well as other codenames and nicknames, including "Zeke", "Hamp" and "Hap".
When it was introduced early in World War II, the Zero was the best carrier-based fighter in the world, combining excellent maneuverability and very long range. In early combat operations, the Zero gained a legendary reputation as a "dogfighter", gaining the outstanding kill ratio of 12 to 1,[3 ] but by 1942, a combination of new tactics and the introduction of better equipment enabled the Allied pilots to engage the Zero on more equal terms. The Imperial Japanese Naval Air Service (IJNAS) also frequently used the type as a land-based fighter. By 1943, inherent design weaknesses and the increasing lack of more powerful aircraft engines meant that the Zero became less effective against newer enemy fighters that possessed greater firepower, armor, speed, and approached the Zero's maneuverability. Although the Mitsubishi A6M was outdated by 1944, it was never totally supplanted by the newer Japanese aircraft types. During the final years of the War in the Pacific, the Zero was used in kamikaze operations.
The Mitsubishi A5M fighter was just starting to enter service in early 1937 when the Imperial Japanese Navy started looking for its eventual replacement. In May they issued specification 12-Shi for a new carrier-based fighter, sending it to Nakajima and Mitsubishi. Both firms started preliminary design work while they awaited more definitive requirements to be handed over in a few months.
Based on the experiences of the A5M in China, the Navy sent out updated requirements in October calling for a speed of 500 km/h (310 mph) at 4,000 m (13,120 ft) and a climb to 3,000 m (9,840 ft) in 3.5 min. They needed an endurance of two hours at normal power, or six to eight hours at economical cruising speed (both with drop tanks). Armament was to consist of two 20 mm cannon, two 7.7 mm (.303 in) machine guns and two 30 kg (70 lb) or 60 kg (130 lb) bombs. A complete radio set was to be mounted in all airplanes, along with a radio direction finder for long-range navigation. The maneuverability was to be at least equal to that of the A5M, while the wing span had to be less than 12 m (39 ft) to fit on the carriers. All this was to be achieved with such engines as were available at the time, which was another limitation (the Zero's power plant seldom reached 1,000 horsepower in any of its variants).
Nakajima's team considered the new requirements unachievable and pulled out of the competition in January. Mitsubishi's chief designer, Jiro Horikoshi, felt that the requirements could be met, but only if the aircraft could be made as light as possible. Every weight-saving method was used. Most of the airplane was built of T-7178 aluminum, a top-secret aluminum alloy developed by the Japanese just for this aircraft. It was lighter and stronger than the normal aluminum used at the time, but more brittle. In addition, no armor was carried for the pilot, engine or other critical points of the aircraft, and the self-sealing fuel tanks that were becoming common at the time were also left off. This made the Zero lighter and more agile than most other aircraft at the start of the war, but that also made it prone to catching fire and exploding when struck by enemy rounds.
With its low-wing cantilever monoplane layout, retractable wide-set landing gear and enclosed cockpit, the design was one of the most modern in the world. The Zero had a fairly high-lift, low-speed wing with a very low wing loading; combined with the light weight this gave it a very low stalling speed of well below 60 kn (110 km/h; 69 mph). This is the reason for the phenomenal turning ability of the airplane, allowing it to turn more sharply than any Allied fighter of the time. Roll rate is enhanced by servo tabs on the ailerons which deflect opposite to the ailerons and make the control force much lighter. The disadvantage is that they reduce the maximum roll effect at full travel. At 160 mph (260 km/h) the A6M2 had a roll rate of 56° per second. Because of wing flexibility, roll effectiveness dropped to near zero at about 483 km/h (300 mph) indicated airspeed.
The A6M is universally known as the Zero from its Japanese Navy type designation, Type 0 Carrier Fighter (Rei shiki Kanjō sentōki, 零式艦上戦闘機), taken from the last digit of the Imperial year 2600 (1940), when it entered service. In Japan it was unofficially referred to as both Rei-sen and Zero-sen; Japanese pilots most commonly called their plane Zero-sen.
The official Allied code name was "Zeke" in keeping with the practice of giving male names to Japanese fighters, female names to bombers, bird names to gliders and tree names to trainers."Zeke" was part of the first batch of "hillbilly" code names assigned by Captain Frank T. McCoy, of Tennessee, who wanted quick, distinctive, easy to remember names. When in 1942 the Allied code for Japanese aircraft was introduced, he logically chose "Zeke" for the "Zero." Later, two variants of the fighter, not immediately identified as such, received their own code names: the A6M2-N (floatplane version of the Zero) was called Rufe and the A6M3-32 variant was initially called Hap. After objections from General "Hap" Arnold, C/O of the USAAF, the name was changed to Hamp.
The first Zero (pre-series A6M2) were operative in July 1940. On 13 September 1940, the Zeros scored their first air-to-air victories when 13 A6M2s led by Lieutenant Saburo Shindo attacked 27 Soviet-built Polikarpov I-15s and I-16s of the Chinese Nationalist Air Force, shooting down all the fighters for no losses. Before they were redeployed a year later, the Zeros had shot down 99 Chinese aircraft (266 according to other sources).
At the time of Pearl Harbor, there were 420 Zeros active in the Pacific. The carrier-borne Model 21 was the type encountered by the Americans, often much further from its carriers than expected, with a mission range of over 2,600 km (1,600 mi). Thanks to a combination of excellent maneuverability and firepower, the Zero easily disposed of the motley collection of Allied aircraft sent against it in the Pacific in 1941, while its tremendous range allowed it to appear over distant battlefronts and give Allied commanders the belief there must be several times as many Zeros as there actually were. So the Zero quickly gained a great reputation. However, the Zero failed to achieve complete air superiority due to the development of suitable tactics and new aircraft by the Allies. During World War II, the Zero destroyed at least 1,550 American aircraft.
The Japanese ace Saburo Sakai described how the resilience of early Allied aircraft was a factor in preventing the Zeros from attaining total domination:
|“||I had full confidence in my ability to destroy the Grumman and decided to finish off the enemy fighter with only my 7.7 mm machine guns. I turned the 20mm. cannon switch to the 'off' position, and closed in. For some strange reason, even after I had poured about five or six hundred rounds of ammunition directly into the Grumman, the airplane did not fall, but kept on flying. I thought this very odd—it had never happened before—and closed the distance between the two airplanes until I could almost reach out and touch the Grumman. To my surprise, the Grumman's rudder and tail were torn to shreds, looking like an old torn piece of rag. With his plane in such condition, no wonder the pilot was unable to continue fighting! A Zero which had taken that many bullets would have been a ball of fire by now.||”|
Designed for attack, the Zero gave precedence to long range, maneuverability, and firepower at the expense of protection—most had no self-sealing tanks or armor plate—thus many Zeros and their pilots were too easily lost in combat. During the initial phases of the Pacific conflict, the Japanese trained their aviators far more strenuously than their Allied counterparts. Thus, unexpectedly heavy pilot losses at the Coral Sea and Midway made them difficult to replace.
With the extreme agility of the Zero, the Allied pilots found that the appropriate combat tactic against it was to remain out of range and fight on the dive and climb. By using speed and resisting the deadly error of trying to out-turn the Zero, eventually cannon or heavy machine guns (.50 caliber) could be brought to bear and a single burst of fire was usually enough to down it. Such "boom-and-zoom" tactics were successful in the China Burma India Theater (CBI) against similarly maneuverable Japanese Army aircraft such as the Nakajima Ki-27 and Ki-43 by the "Flying Tigers" of the American Volunteer Group (AVG). AVG pilots were trained to exploit the advantages of their P-40s; very sturdy, heavily armed, generally faster in a dive and in level flight at low altitude, with a good rate of roll.
Another important maneuver was then-Lieutenant Commander John S. "Jimmy" Thach's "Thach Weave", in which two fighters would fly about 60 m (200 ft) apart. When a Zero latched onto the tail of one of the fighters, the two planes would turn toward each other. If the Zero followed its original target through the turn, it would come into a position to be fired on by his target's wingman. This tactic was used to good effect at the Battle of the Coral Sea, at the Battle of Midway, and over the Solomon Islands.
The American military discovered many of the A6M's unique attributes when they recovered the Akutan Zero—a mostly-intact specimen on Akutan Island in the Aleutians. Flight Petty Officer Tadayoshi Koga was losing oil and attempted an emergency landing, but the Zero flipped over in soft ground and the pilot died of head wounds. The relatively undamaged fighter was shipped to North Air Station, North Island, San Diego. Subsequent testing of the repaired A6M revealed not only its strengths, but also its deficiencies in design and performance.
When the powerful P-38 Lightning, F6F Hellcat, and F4U Corsair appeared in the Pacific theater, the A6M, with its low-powered engine, lost its competitiveness. In combat with an F6F or F4U, the only positive thing that could be said of the Zero at this stage of the war was that in the hands of a skillful pilot it could maneuver as well as most of its opponents. But the ever-decreasing number of experienced Japanese aviators became a significant factor in Allied successes.
Nonetheless, until the end of the war, in competent hands, the Zero could still be deadly. Due to the scarcity of high-powered aviation engines and problems with planned successor models, the Zero remained in production until 1945, with over 11,000 of all variants produced.
Capt. Eric Brown, CBE, DSC, AFC, RN, Chief Naval Test Pilot and C.O. Captured Enemy Aircraft Flight recalls how he was impressed when they tested the plane. “I don’t think I have ever flown a fighter that could match the rate of turn of the Zero. The Zero had ruled the roost totally and was the finest fighter in the world until mid-1943 [3 ]
The first A6M1 prototype was completed in March 1939, powered by the 580 kW (780 hp) Mitsubishi Zuisei 13 engine with a two-blade propeller. It first flew on 1 April, and passed testing in a remarkably short period of time. By September, it had already been accepted for Navy testing as the A6M1 Type 0 Carrier Fighter, with the only notable change being a switch to a three-bladed propeller to cure a vibration problem.
While the Navy was testing the first two prototypes, they suggested that the third be fitted with the 700 kW (940 hp) Nakajima Sakae 12 engine instead. Mitsubishi had its own engine of this class in the form of the Kinsei, so they were somewhat reluctant to use the Sakae. Nevertheless when the first A6M2 was completed in January 1940, the Sakae's extra power pushed the performance of the plane well past the original specifications.
The new version was so promising that the Navy had 15 built and shipped to China before they had completed testing. They arrived in Manchuria in July 1940, and first saw combat over Chungking in August. There they proved to be completely untouchable by the Polikarpov I-16s and I-153s that had been such a problem for the A5Ms currently in service. In one encounter, 13 Zeros shot down 27 I-15s and I-16s in under three minutes without loss. After hearing of these reports the Navy immediately ordered the plane into production as the Type 0 Carrier Fighter, Model 11. Reports of the Zero's performance filtered back to the US slowly. There they were dismissed by most military officials, who felt it was impossible for the Japanese to build such an aircraft.
After the delivery of only 65 planes by November 1940, a further change was worked into the production lines, which introduced folding wingtips to allow them to fit on aircraft carriers. The resulting Model 21 would become one of the most produced versions early in the war. When the lines switched to updated models, 740 Model 21s were completed by Mitsubishi, and another 800 by Nakajima. Two other versions of the Model 21 were built in small numbers, the Nakajima-built A6M2-N "Rufe" floatplane (based on the model 11 with a slightly modified tail), and the A6M2-K two-seat trainer of which a total of 508 were built by Hitachi and the Sasebo Naval Air Arsenal.
In late 1941, Nakajima introduced the Sakae 21, which used a two-speed supercharger for better altitude performance, and increased power to 840 kW (1,130 hp). Plans were made to introduce the new engine into the Zero as soon as possible.
The new Sakae was slightly heavier and somewhat longer due to the larger supercharger, which moved the center of gravity too far forward on the existing airframe. To correct for this the engine mountings were cut down by 20 cm (8 in), moving the engine back towards the cockpit. This had the side effect of reducing the size of the main fuel tank (located to the rear of the engine) from 518 L (137 US gal) to 470 L (120 US gal).
The only other major changes were to the wings, which were simplified by removing the Model 21's folding tips. This changed the appearance enough to prompt the US to designate it with a new code name, Hap. This name was short-lived, as a protest from USAAF commander General Henry "Hap" Arnold forced a change to "Hamp". Soon after, it was realized that it was simply a new model of the "Zeke". The wings also included larger ammunition boxes, allowing for 100 rounds for each of the 20 mm cannon.
The wing changes had much greater effects on performance than expected. The smaller size led to better roll, and their lower drag allowed the diving speed to be increased to 670 km/h (420 mph). On the downside, maneuverability was reduced, and range suffered due to both decreased lift and the smaller fuel tank. Pilots complained about both. The shorter range proved a significant limitation during the Solomons campaign of 1942.
The first Model 32 deliveries began in April 1942, but it remained on the lines only for a short time, with a run of 343 being built.
In order to correct the deficiencies of the Model 32, a new version with the Model 21's folding wings, new in-wing fuel tanks and attachments for a 330 L (90 US gal) drop tank under each wing were introduced. The internal fuel was thereby increased to 570 L (137 US gal) in this model, regaining all of the lost range.
As the airframe was reverted from the Model 32 and the engine remained the same, this version received the navy designation Model 22, while Mitsubishi called it the A6M3a. The new model started production in December, and 560 were eventually produced. This company constructed some examples for evaluation, armed with 30 mm Type 5 Cannon, under denomination of A6M3b (model 22b).
The A6M4 designation was applied to two A6M2s fitted with an experimental turbo-supercharged Sakae engine designed for high-altitude use. The design, modification and testing of these two prototypes was the responsibility of the First Naval Air Technical Arsenal (第一海軍航空廠) at Yokosuka and took place in 1943. Lack of suitable alloys for use in the manufacture of the turbo-supercharger and its related ducting caused numerous ruptures of the ducting resulting in fires and poor performance. Consequently, further development of the A6M4 was cancelled. The program still provided useful data for future aircraft designs and, consequently, the manufacture of the more conventional A6M5, already under development by Mitsubishi Jukogyo K.K., was accelerated. 
Considered the most effective variant, the Model 52 was developed to face the powerful American Hellcat and Corsair, superior mostly for engine power and armament.  The variant was a modest update of the A6M3 Model 22, with non-folding wing tips and thicker wing skinning to permit faster diving speeds, plus an improved exhaust system. The latter used four ejector exhaust stacks, providing an increment of thrust, projecting along each side of the forward fuselage. The new exhaust system required modified "notched" cowl flaps and small rectangular plates which were riveted to the fuselage, just aft of the exhausts. Two smaller exhaust stacks exited via small cowling flaps immediately forward of and just below each of the wing leading edges. The improved roll-rate of the clipped-wing A6M3 was now built in.
The A6M5 had a maximum speed of 540 km/h (340 mph) and reach a height of 8,000 m (26,250 ft) in nine minutes, 57 seconds. Other variants were the night fighter A6M5d-S (modified for night combat, armed with one 20 mm Type 99 cannon, inclined back to the pilot's cockpit) and A6M5-K "Zero-Reisen"(model l22) tandem trainer version, also manufactured by Mitsubishi.
This was similar to the A6M5c, but with self-sealing wing tanks and a Nakajima Sakae 31a engine featuring water-methanol engine boost.
Similar to the A6M6 but intended for attack or Kamikaze role.
Similar to the A6M6 but with the Sakae (now out of production) replaced by the Mitsubishi Kinsei 62 engine with 1,560 hp (1,164 kW), 60% more powerful than the engine of the A6M2. This resulted in an extensively modified cowling and nose for the aircraft. The carburetor intake was much larger, a long duct like that on the Nakajima B6N Tenzan was added, and a large spinner—like that on the Yokosuka D4Y Suisei with the Kinsei 62—was mounted. The larger cowling meant deletion of the fuselage mounted machine gun, but armament was otherwise unchanged from the Model 52 Hei (20 mm cannon x 2; 13 mm/.51 in MG x 2). In addition, the Model 64 was modified to carry two 150 L (40 US gal) drop tanks on either wing in order to permit the mounting of a 250 kg (550 lb) bomb on the underside of the fuselage. Two prototypes were completed in April 1945 but the chaotic situation of Japanese industry and the end of the war obstructed the start of the ambitious program of production for 6,300 machines, none being completed. 
Several Zero fighters survived the war and are on display in Japan (in Aichi, Tokyo's Science Museum, Hiroshima, Hamamatsu, MCAS Iwakuni, and Shizuoka), China (in Beijing), United States (at the National Air and Space Museum, National Museum of the United States Air Force, the National Museum of Naval Aviation, the Pacific Aviation Museum, the San Diego Air and Space Museum), and the UK (Duxford) as well as the Auckland War Memorial Museum in New Zealand. A restored A6M2-21 (V-173 retrieved as a wreck after the war, and later found to have been flown by Saburo Sakai at Lae) is on display at the Australian War Memorial in Canberra.
A number of flyable Zero airframes exist; most have had their engines replaced with similar American units; only one, the Planes of Fame Museum's example, bearing tail number "61-120" (see external link below) has the original Sakae engine. Although not truly a survivor, the "Blayd" Zero is a reconstruction based on templating original Zero components recovered from the South Pacific. In order to be considered a "restoration," the builders used a small fraction of parts from original Zero landing gear in the reconstruction. The aircraft is now on display at the Fargo Air Museum in Fargo, North Dakota.
The rarity of flyable Zeros accounts for the use of single-seat T-6 Texans, modified externally and painted in Japanese markings, to stand in for the fighter in the films Tora! Tora! Tora!, The Final Countdown, and many other television and film depictions of the aircraft. One Model 52 was used during the production of Pearl Harbor.
Data from The Great Book of Fighters