The Terror of the Pacific: the A6M Zero
Mitsubishi A6M Zero in Flight
Welcome back to Brooke In The Air! We’ve covered enough of the Allied warplanes for awhile, it’s time to switch sides, metaphorically, and analyze the Mitsubishi A6M Zero superiority fighter!
We will have analysis of the Hilton Cleveland Downtown and food up next week, so stay tuned for those!
INTRO TO THE ZEKE
The Mitsubishi A6M "Zero" is a long-range carrier-based fighter aircraft formerly manufactured by Mitsubishi Aircraft Company, a part of Mitsubishi Heavy Industries. It was operated by the Imperial Japanese Navy (IJN) from 1940 to 1945.
Zeroes on the flight deck of IJN Akagi, 1941.
Officially, the A6M was designated as the Mitsubishi Navy Type 0 carrier fighter (零式艦上戦闘機, rei-shiki-kanjō-sentōki), or the Mitsubishi A6M Rei-sen.
The A6M was usually referred to by its pilots as the Reisen (零戦, zero fighter), "0" being the last digit of the imperial year 2600 (1940) when it entered service with the Imperial Navy. The official Allied reporting name was "Zeke", although the name "Zero" was used colloquially as well. 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 Nashville, Tennessee (assigned to the Allied Technical Air Intelligence Unit at Eagle Farm Airport in Australia), who wanted quick, distinctive, easy-to-remember names.
The Zero is considered to have been the most capable carrier-based fighter in the world when it was introduced early in World War II, combining excellent maneuverability and very long range. The Imperial Japanese Navy Air Service also frequently used it as a land-based fighter on behalf or for the Imperial Army.
Combat footage of A6Ms in Formation Flight
In early combat operations, the Zero gained a reputation as a dogfighter, achieving an outstanding kill ratio of 12 to 1, but by mid-1942 a combination of new tactics and the introduction of better equipment and well-trained pilots enabled Allied pilots to engage the Zero on generally equal terms. By 1943, the Zero was less effective against newer Allied fighters.
The Zero lacked hydraulic boosting for its ailerons and rudder, rendering it difficult to maneuver at high speeds. Lack of self-sealing fuel tanks also made it more vulnerable than its contemporaries.
By 1944, with Allied fighters approaching the A6M's levels of maneuverability and consistently exceeding its firepower, armor, and speed, the A6M had largely become outdated as a fighter aircraft.
As design delays and production difficulties plus lack of available supplies hampered the introduction of newer Japanese aircraft models, the Zero continued to serve in a front-line role until the end of the war in the Pacific. During the final phases, it was also adapted for use in kamikaze operations. Japan produced more Zeros than any other model of combat aircraft during the war.
DESIGN STAGES
The Mitsubishi A5M fighter was just entering service in early 1937, when the Imperial Japanese Navy started looking for its eventual replacement. On 5 October 1937, it issued "Planning Requirements for the Prototype 12-shi Carrier-based Fighter", sending them to Nakajima and Mitsubishi. Both firms started preliminary design work while awaiting more definitive requirements to come out a few months later.
Based on the experiences of the A5M in China, the IJN sent out updated requirements in October, calling for a speed of 270 kn (310 mph; 500 km/h) at 4,000 m (13,000 ft) and a climb to 3,000 m (9,800 ft) in 9.5 minutes. With drop tanks, the IJN wanted an endurance of two hours at normal power, or six to eight hours at economical cruising speed. Armament was to consist of two 20 mm cannons, two 7.7 mm. machine guns and two 60 kg (130 lb) bombs.
A complete radio set was to be mounted in all aircraft, 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 wingspan had to be less than 12 m (39 ft) to allow for use on aircraft carriers.
While Nakajima's team considered the new requirements unachievable and pulled out of the competition in January, Mitsubishi's chief designer, Jiro Horikoshi, thought that the requirements could be met, but only if the aircraft were made as light as possible. Every possible weight-saving measure was incorporated into the design.
Most of the aircraft was built of a new top-secret aluminium alloy developed by Sumitomo Metal Industries in 1936. Called "extra super duralumin", it was lighter, stronger and more ductile than other alloys used at the time but was prone to corrosive attack, which made it brittle. This detrimental effect was countered with a zinc chromate anti-corrosion coating applied after fabrication.
Zeros ready for Launch, IJN Kaga, 1943
Crucially, no armour protection was provided for the pilot, engine or other critical points of the aircraft, and self-sealing fuel tanks, which were becoming common among other combatants, were not used.
This made the Zero lighter, more maneuverable, and one of the longest-ranged single-engine fighters of World War II, which made it capable of searching out an enemy hundreds of kilometres away, bringing it to battle, then returning to its base or aircraft carrier. However, that tradeoff in weight and construction also made it prone to catching fire and exploding when struck by enemy fire.
With its low-wing cantilever monoplane layout, retractable wide-set conventional landing gear, and enclosed cockpit, the Zero was one of the most modern carrier-based aircraft in the world at the time of its introduction. It had a fairly high-lift, low-speed wing with very low wing loading. Combined with its light weight, this resulted in a very low stalling speed of well below 60 kn (110 km/h; 69 mph). This was the main reason for its phenomenal maneuverability, allowing it to out-turn any Allied fighter of the time. Early models were fitted with servo tabs on the ailerons after pilots complained that control forces became too heavy at speeds above 300 kilometres per hour (190 mph). They were discontinued on later models after it was found that the lightened control forces were causing pilots to overstress the wings during vigorous maneuvers.
OPERATIONS
The first Zeros (pre-series of 15 A6M2) went into operation with the 12th Rengo Kōkūtai in July 1940. On 13 September 1940, the Zeros scored their first air-to-air victories when 13 A6M2s led by Lieutenant Saburo Shindo, escorting 27 G3M "Nell" medium-heavy bombers on a raid of Chongqing, attacked 34 Soviet-built Polikarpov I-15s and I-16s of the Chinese Nationalist Air Force, claimed "all 27" of the Chinese fighters shot down without loss to themselves. However Major Louie Yim-qun had in fact nursed his I-15 riddled with 48 bullet holes back to base, and Lieutenant Gao Youxin claimed to have shot down one Zero, but at most 4 Zeroes sustained some damage in the 1/2 hour-long dogfight over Chongqing. By the time they were redeployed a year later, the Zeros had shot down 99 Chinese aircraft (up to 266 according to other sources).
PsyOps
A6M Remnants in 1945, Zeroes Discarded
At the time of the attack on Pearl Harbor, 521 Zeros were active in the Pacific, 328 in first-line units. The carrier-borne Model 21 was the type encountered by the Americans. Its tremendous range of over 2,600 kilometres (1,600 mi) allowed it to range farther from its carrier than expected, appearing over distant battlefronts and giving Allied commanders the impression that there were several times as many Zeros as actually existed.
The Zero quickly gained a fearsome reputation. Thanks to a combination of unsurpassed maneuverability—compared to contemporary Axis fighters—and excellent firepower, it easily disposed of Allied aircraft sent against it in the Pacific in 1941. It proved a difficult opponent even for the Supermarine Spitfire.
"The RAF pilots were trained in methods that were excellent against German and Italian equipment but suicide against the acrobatic Japs", as Lieutenant General Claire Lee Chennault noted.
Although not as fast as the British fighter, the Zero could out-turn the Spitfire with ease, sustain a climb at a very steep angle, and stay in the air for three times as long.
TACTICS EVALUATION
Allied pilots soon developed tactics to cope with the Zero. Because of its extreme agility, engaging a Zero in a traditional turning dogfight was likely to be fatal. It was better to swoop down from above in a high-speed pass, fire a quick burst, then climb quickly back up to altitude. A short burst of fire from heavy machine guns or cannon was often enough to bring down the fragile Zero. These tactics were regularly employed by Grumman F4F Wildcat fighters during Guadalcanal defense through high-altitude ambush, which was possible with an early warning system consisting of coastwatchers and radar. Such "boom-and-zoom" tactics were also successfully used in the China Burma India Theater by the "Flying Tigers" of the American Volunteer Group (AVG) against similarly maneuverable Japanese Army aircraft such as the Nakajima Ki-27 "Nate" and Nakajima Ki-43 "Oscar". AVG pilots were trained by their commander Claire Chennault to exploit the advantages of their P-40 Warhawks, which were very sturdy, heavily armed, generally faster in a dive, and level flight at low altitude, with a good rate of roll.
Another important maneuver was Lieutenant Commander John S. "Jimmy" Thach's "Thach Weave", in which two fighters would fly about 60 m (200 ft) apart. If a Zero latched onto the tail of one of the fighters, the two aircraft would turn toward each other. If the Zero followed his original target through the turn, he would come into a position to be fired on by the target's wingman. This tactic was first used to good effect during the Battle of Midway and later over the Solomon Islands.
Ultimately, many highly experienced Japanese aviators were lost in combat, resulting in a progressive decline in pilot quality, which became a significant factor in Allied successes. Unexpected heavy losses of pilots at the Battles of the Coral Sea and Midway dealt the Japanese carrier air force a blow from which it never fully recovered.
TESTIMONIES
Throughout the Battle of Midway Allied pilots expressed a high level of dissatisfaction with the F4F Wildcat. Captain Elliott Buckmaster, commanding officer of USS Yorktown notes:
Naval Zeroes on the island of Rabaul, c. 1943.
The fighter pilots are very disappointed with the performance and length of sustained fire power of the F4F-4 airplanes. The Zero fighters could easily outmaneuver and out-climb the F4F-3, and the consensus of fighter pilot opinion is that the F4F-4 is even more sluggish and slow than the F4F-3. It is also felt that it was a mistake to put 6 guns on the F4F-4 and thus to reduce the rounds per gun. Many of our fighters ran out of ammunition even before the Jap dive bombers arrived over our forces; these were experienced pilots, not novices.
They were astounded by the Zero's superiority:
In the Coral Sea, they made all their approaches from the rear or high side and did relatively little damage because of our armor. It also is desired to call attention to the fact that there was an absence of the fancy stunting during pull outs or approaches for attacks. In this battle, the Japs dove in, made the attack and then immediately pulled out, taking advantage of their superior climb and maneuverability. In attacking fighters, the Zeros usually attacked from above rear at high speed and recovered by climbing vertically until they lost some speed and then pulled on through to complete a small loop of high wing over which placed them out of reach and in position for another attack. By reversing the turn sharply after each attack the leader may get a shot at the enemy while he is climbing away or head on into a scissor if the Jap turns to meet it.
In contrast, Allied fighters were designed with ruggedness and pilot protection in mind. The Japanese ace Saburō Sakai described how the toughness of early Grumman aircraft was a factor in preventing the Zero 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.
Zero upon Takeoff from IJN Hiryu, 1942
Allied Analyses
Chinese Opinions
The Japanese deployed the A6M during the Second Sino-Japanese War. Inevitably some aircraft were lost, with at least two falling more-or-less intact into Chinese hands. The first known example, an A6M2 (the 12th of the 15th pre-production aircraft, Serial V-110), fell near Fainan Island. On 18 September 1940 a team, including Western volunteers assisting the Chinese, examined the wreck. It was largely intact, and a detail report was compiled and sent to the U.S. The second, an A6M2-21 (Serial V-173), made a forced landing near Tietsan airfield 17 February 1941. The pilot was shot before he could destroy his plane, the fuel system fixed, and it was taken into Chinese service. The plane was extensively flown and studied by a team which included Gerhard Neumann, and a detailed and illustrated report was sent to Washington. Overall they were impressed with the quality of the aircraft, less so by the performance—although this was later put down to using 85 octane fuel rather than the 100 octane required by the Sakae engine.
American Opinions
The American military discovered many of the A6M's unique attributes when they recovered a largely intact specimen of an A6M2, the Akutan Zero, on Akutan Island in the Aleutians. During an air raid over Dutch Harbor on 4 June 1942, one A6M fighter was hit by ground-based anti-aircraft fire. Losing oil, Flight Petty Officer Tadayoshi Koga attempted an emergency landing on Akutan Island about 20 miles (32 km) northeast of Dutch Harbor, but his Zero flipped over on soft ground in a sudden crash-landing. Koga died instantly of head injuries (his neck was broken by the tremendous impact), but his wingmen hoped he had survived and so went against Japanese doctrine to destroy disabled Zeros. The relatively undamaged fighter was found over a month later by an American salvage team and was shipped to Naval Air Station North Island, where testing flights of the repaired A6M revealed both strengths and deficiencies in design and performance.
The experts who evaluated the captured Zero found that the plane weighed about 2,360 kg (5,200 lb) fully loaded, some 1,260 kg (2,780 lb) lighter than the F4F Wildcat, the standard United States Navy fighter of the time. The A6M's airframe was "built like a fine watch"; the Zero was constructed with flush rivets, and even the guns were flush with the wings. The instrument panel was a "marvel of simplicity… with no superfluities to distract [the pilot]". What most impressed the experts was that the Zero's fuselage and wings were constructed in one piece, unlike the American method that built them separately and joined the two parts together. The Japanese method was much slower but resulted in a very strong structure and improved close maneuverability.
British Opinions
Captain Eric Brown, the chief naval test pilot of the Royal Navy, recalled being impressed by the Zero during tests of captured aircraft. "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."
CULMINATION
Wrecked Zero on Rabaul, 1944.
When the Lockheed P-38 Lightning, armed with four "light barrel" AN/M2 .50 cal. Browning machine guns and one 20 mm autocannon, and the Grumman F6F Hellcat and Vought F4U Corsair, each with six AN/M2 .50 calibre Browning guns, appeared in the Pacific theater, the A6M, with its low-powered engine and lighter armament, was hard-pressed to remain competitive. 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. Nonetheless, in competent hands, the Zero could still be deadly. Because of shortages of high-powered aviation engines and problems with planned successor models, namely the superior Mitsubishi A7M2 Reppū, the Zero remained in production until 1945, with over 10,000 of all variants produced.
VARIANTS
One of Very Few Zeroes Still Flying
A6M1-0, type 0
The first two A6M1 prototypes were 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 within a remarkably short period. 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.
A6M2a, type 0. Model 11
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 Zero well past the original specifications.
A6M2b, type 0. Model 21
After the delivery of the 65th aircraft, 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. A feature was the improved range with 520 L (140 US gal) wing tank and 320 L (85 US gal) drop tank. When the lines switched to updated models, 740 Model 21s had been 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.
A6M3, type 0. Model 32
In 1941, Nakajima introduced the Sakae 21 engine, which used a two-speed supercharger for better altitude performance, and increased power to 831 kW (1,130 hp). A prototype Zero with the new engine was first flown on 15 July 1941.
The new Sakae engine 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 back by 185 mm (7.3 in) to move the engine toward the cockpit. This had the side effect of reducing the size of the main fuselage fuel tank (located between the engine and the cockpit) from 518 L (137 US gal) to 470 L (120 US gal). The cowling was redesigned to enlarge the cowl flaps, revise the oil cooler air intake, and move the carburetor air intake to the upper half of the cowling. Overall this was a disappointment.
This variant was flown by only a small number of units, and only 343 were built. One example survives today, and is on display at the Tachiarai Peace Memorial Museum in Tachiarai, Fukuoka, Japan.
A6M3, type 0. Model 22
In order to correct the deficiencies of the Model 32, a new version with folding wingtips and redesigned wing was introduced. The fuel tanks were moved to the outer wings, fuel lines for a 330 L (87 US gal) drop tank were installed under each wing and the internal fuel capacity was increased to 570 L (150 US gal). More importantly, it regained its capabilities for long operating ranges, similar to the previous A6M2 Model 21, which was vastly shortened by the Model 32.
However, before the new design type was accepted formally by the Navy, the A6M3 Model 22 already stood ready for service in December 1942. Approximately 560 aircraft of the new type had been produced in the meantime by Mitsubishi Jukogyo K.K.
A6M4, type 0. Model 41/42
Mitsubishi is unable to state with certainty that it ever used the designation "A6M4" or model numbers for it. However, "A6M4" does appear in a translation of a captured Japanese memo from a Naval Air Technical Arsenal, titled Quarterly Report on Research Experiments, dated 1 October 1942. It mentions a "cross-section of the A6M4 intercooler" then being designed. Some researchers believe "A6M4" was applied to one or two prototype planes fitted with an experimental turbo-supercharged Sakae engine designed for high altitude. Mitsubishi's involvement in the project was probably quite limited or nil; the unmodified Sakae engine was made by Nakajima. The design and testing of the turbo-supercharger was the responsibility of the First Naval Air - Technical - Arsenal (第一海軍航空廠, Dai Ichi Kaigun Kōkūshō) at Yokosuka. At least one photo of a prototype plane exists. It shows a turbo unit mounted in the forward left fuselage.
A6M5, type 0. Model 52
Sometimes considered as the most effective variant, the Model 52 was developed to again shorten the wings to increase speed and dispense with the folding wing mechanism. In addition, ailerons, aileron trim tab and flaps were revised. Produced first by Mitsubishi, most Model 52s were made by Nakajima. The prototype was made in June 1943 by modifying an A6M3 and was first flown in August 1943. The first Model 52 is said in the handling manual to have production number 3904, which apparently refers to the prototype.
Research by Mr. Bunzo Komine published by Mr. Kenji Miyazaki states that aircraft 3904 through 4103 had the same exhaust system and cowl flaps as on the Model 22. This is partially corroborated by two wrecks researched by Mr. Stan Gajda and Mr. L. G. Halls, production number 4007 and 4043, respectively.
An early production A6M5 Zero with non-separated exhaust. A new exhaust system provided an increment of thrust by aiming the stacks aft and distributing them around the forward fuselage. The new exhaust system required "notched" cowl flaps and heat shields just aft of the stacks. (Please note, however, that the handling manual translation states that the new style of exhaust commenced with number 3904. Whether or not this is correct, indicates retrofitting intentions, refers to the prototype but not to all subsequent planes, or is in error, is unclear.)
Numerous sub-variants were developed and too numerous to go over here.
Over 10,000 examples of the Zero were produced from 1937-1945.
