|
The Mitsubishi A6M was a light-weight naval fighter aircraft employed by
the Japanese from 1940-45. More widely known by its Navy designation, Type 0
Carrier Fighter, or Zero, the plane gained a legendary reputation. A
combination of excellent manuverability and very long range made it the best
fighter of its era, but design weaknesses and lack of more powerful engines
eventually doomed it.
Background
The Mitsubishi A5M was just starting to enter service in early 1937 when
the IJN 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 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. The new requirements called for a speed of 500km/h
at 4000m, and a climb to 3000m in 3.5min. They needed an endurance of 2
hours at normal power, or 6 to 8 hrs at economical cruising speed (both with
drop tanks). Armament was to consist of two 20mm cannons and two 7.7mm
machine guns, and two 30kg or 60kg bombs. A complete radio set was to be
mounted in all planes, along with a radio direction finder for long-range
navigation. Finally the maneuverability was to be at least equal to A5M,
while the wing span had to be less than 12m to fit on the carriers.
Nakajima's team thought the new requirements were ridiculous 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, and
the designers made extensive use of the new duralumin alloy. With its
low-wing cantilever monoplane layout, retractable wide-set landing and
enclosed cockpit, the design was not only much more modern than any the Navy
had used in the past, it was one of the most modern in the world.
A6M1, Type 0 Prototypes
The first A6M1 prototype was completed in March 1939, powered by the
780hp Mitsubishi Zuisei 13 engine with a two-bladed propeller. It first flew
on April 1st, 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.
A6M2, Type 0 Model 11
While the Navy was testing the first two prototypes, they suggested that
the third be fitted with the 940hp 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-16's and I-153's that had
been such a problem for the A5M's currently in service. In one encounter 13
Zeros shot down 27 I-15 and I-16's 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 planners, who felt it was impossible for the
Japanese to build such an aircraft. Others were not so sure, and techniques
were developed by Butch O'Hare to combat them just in case.
A6M2, Type 0 Model 21
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 the 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 21's were completed by Mitsubishi, and
another 800 by Nakajima. Two other versions of the Model 21 were built in
small numbers, the A6M2-N "Rufe" floatplane and A6M2-K two-seat trainer.
Model 21 Wing span 39ft Length 29ft 9in Engine 925hp Max Speed 336mph (
at 20000ft ) Ceiling 33500ft Max weight 5300lb Armament 2 x 7.7mm MG, 2 x
20mm cannon; 2 x 66lb or 1 x 132lb bombs; 2 fixed 250kg bombs for kamikaze
A6M3, Type 0 Model 32
In late 1941 Nakajima introduced the Sakae 21, which used a two speed
supercharger for better altitude performance, and increased power to
1,130hp. 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
8 inches, 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 litres to 470 litres.
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 Hamp, before realizing it
was simply a new model of the Zeke. The wings also included larger
ammunition boxes, allowing for 100 rounds for each of the 20mm cannon.
The wing changes had much a 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 360kts. On the downside, manuverability was
reduced, and range suffered both due to 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.
A6M3, Type 0 Model 22
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 litre drop tank under each wing was introduced. The internal fuel was
thereby increased to 570 litres in this model, gaining back all of the lost
range.
In an example of somewhat odd naming, the Navy referred to this version
as the Model 22, while Mitsubishi called it the A6M3a. The new model started
production in December, and 560 were eventually produced.
A6M4
The A6M4 is a subject of some debate. Most sources refer to an
experimental turbocharged version of the Zero for high altitude use, but
only a single mention of the A6M4 can be found in text and it does not
mention much.
At the time of Pearl Harbor there were only 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 1600 miles. They were superior to all current Allied
fighters in the Pacific and remained unchallenged until early 1943, although
in competent hands the Zero was deadly until the end of the war. Because of
their reputation and ease of manufacture the Zero remained in production
until the end, with over 11,000 of all types produced.
Designed for attack the Zero gave precedence to manoeuvrability and
fire-power at the expense of protection - most had no self-sealing tanks or
armour plate - thus many Zeros were lost too easily in combat. Nevertheless,
many Allied pilots died trying to learn how to fight such an agile aircraft.
The correct combat tactic against Zeros 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 could be brought to bear
and a single burst of fire was usually enough.
When the US had learned the "secret" of the Zero new aircraft such as the
Gruman Hellcat and Vought Corsair were introduced, planes that outperformed
the Zero in every way but maneuverability. To correct for that shortcoming,
US pilots simply had to remember the correct tactics. The result was that
the Model 22s were swept from the skies in huge numbers, and the US Navy's
1:1 kill ratio suddenly jumped to better than 10:1. However Japanese
development did not remain static - newer planes like the George were
excellent fighters and a match for the later US models.
|
