Mitsubishi Zero
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.
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.
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.
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.
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
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.
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.
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.
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