Mitsubishi A6M Reisen
'Zero'
Aircraft Series
Introduction
Genesis and Development
War Prize
The Lean Years
Aircraft Identity
Colour Schemes
Power Plant
Armament
Avionics
Zero and its Opponents
Preserved Zeros
Links
References & Acknowledgments
Home
Royal
Thai Air Force Museum
e-mail
All text material on this site is
© Peter Lewis
1985, 1999
unless otherwise acknowledged
|
|
Development of the A6M Series
The Japanese Navy were among the pioneers in the use
of carrier-borne fighter aircraft, launching the world's first true
aircraft carrier in November 1921, preceding the British HMS Argus by
several months. To equip this vessel, Mitsubishi developed the Type
10 fighter, the first designed specifically for carrier operation -
naval aircraft of other nations at that time were adaptations of existing
land-based fighters. The Type 10 served until 1929, when replaced by
the Type 3 fighter, which was a Nakajima-built adaptation of the British
Gloster Gambet. This aircraft was re-designated the A1N1 while in service,
'A' signifies carrier-based fighter, and 'N' denotes Nakajima manufacture.
The A1N1 was followed by the 1931 Nakajima Type 90 (A2N) biplane and
the 1935 Type 95 (A4N) which was faster but less agile. Mitsubishi then
reclaimed the market from Nakajima with the Type 96 (A5N)
all-metal monoplane fighter. Replacing the earlier A2N and A4N biplanes,
they were superior to all opposition aircraft encountered in the escalating
war over the Chinese mainland. Equally as important, the Type 96 gave
Japanese designers, engineers and craftsmen experience with techniques
such as minimising drag, flush riveting, weight saving, and the installation
of radial engines into high-speed airframes.
Even as the Type 96 was put into service in 1937, it was realised that
the Navy required a fighter of much greater range for deep penetration
escort duties in China, and that the Type 96 would soon be obsolete
compared to American and European equipment, which was already being
fitted with retractable landing gear and much heavier firepower.
Coupled with this realisation of the limitations of the over-land performance
of the Type 96, was a shift in the beliefs held by the Japanese Naval
Command on the theory and practice of naval aviation. Tradition held
that naval aircraft were an adjunct to the big gun; useful for reconnaissance,
defence, spotting and hindering the enemy until the battleships could
be bought to bear on him. This viewpoint, which had been destroyed in
respect to land-based aviation by World War 1, was prevalent among other
Naval powers until well into World War 2. By adopting the philosophy
of the naval air force as an independent arm - fighting and securing
superiority well beyond the reach of naval artillery - the Japanese
were several years ahead of other nations in producing a series of specialised
aircraft well suited to specific tasks. This was at variance with the
multirole aircraft concept adopted by other naval powers, a concept
that led to such machines as the Fairey Swordfish.
As a result of these experiences and discussions, the Imperial Navy
in 1937 issued specifications for the 12-Shi (12th year since Emperor
Hirohito's reign started in 1926) carrier-borne fighter. These specifications
demanded speed, rate of climb and armament equal to the highest levels
in the world, coupled with unheard of range and exceptional maneuverability.
Mitsubishi formed a design team under Jiro Horikoshi to study the proposal.
Nakajima decided that the Navy's demands were impossible, and told them
that they were withdrawing from the competition.
Horikoshi, having retained and strengthened the Type 96 design team,
had the project formulated by January 1938. Yoshitoshi Sone and Teruo
Tojo performed the calculations, Sone and Yoshio Yoshikawa did the structural
work, Denichiro Inoue and Shotaro Tanaka designed the powerplant installation,
Yoshimi Hatakenaka handled armament and ancillary equipment, and Sadahiko
Kato and Takeyoshi Mori were responsible for landing gear and related
equipment. The Mitsubishi MK2 Zuisei 13 of 875hp was selected, and advanced
techniques utilising extra-super duralumin to ensure lightness, simplicity
and utility were employed. As the specification called only for attack
- and Japanese military philosophy reinforced this viewpoint - safety
devices such as pilot armour and self-sealing fuel tanks were ignored.
Armament was to be a pair of licence-built Oerlikon 20mm cannon (Type
99) in the wings and two 7.7mm machine guns (Type 97 ) in the fuselage.
Construction of the first prototype began later that year and was completed
in March 1939. With no provision for armour, lightness of airframe,
and lack of heavy fittings, the prototype Type 0 weighed 43801b compared
to the prototype Spitfire's 5332lb. Light weight and modest power gave
long range and good performance, but meant that substantially heavier
and more powerful engines could not be fitted without extensive redesign.
As an offensive, rather than a defensive, weapon the Zero' s very success
contained the seeds of its own downfall.
The prototype was declared ready for tests at Mitsubishi's Nagoya factory
on 16th March 1939. Engine tests were run on the 18th, and the next
day it was towed (by ox-cart!) to the airfield at Kagamigahara. Test
pilot Katsuzo Shima lifted it off at 5.30pm on 1st April for the initial
flight. After correction of braking and vibration problems, official
tests of the A6M1 took place and a second, identical prototype was built.
Apart from its lack of outright speed - 304mph instead of the required
315mph - all requirements were met, and the A6M1 was officially accepted
by the Navy on the 14th September 1939. Its military designation became
A6M1 Type 0 Carrier-borne Fighter.
The '0' was derived from the last digit of the Japanese calendar year
in which the aircraft would be placed in full service, 2600 (equivalent
to 1940); in Japanese this became Rei Shiki Sento Ki, Type Zero Fighter,
often shortened to Rei-Sen or Reisen. During the 1940s, the Allies applied
code-names to all known Japanese aircraft, and the A6M2 became 'Zeke',
the later clip-wing A6@13-72 'Hamp', the A6M3-22 'Zeke Mark 2' and the
A6M2-N floatplane version 'Rufe'. By this time the term 'Zero' was already
popular (although British personnel in the Singapore/Malaya theatre
initially knew them as 'Navy Noughts'), and even today people identify
virtually any low-wing radial-engined Japanese fighter as a 'Zero'.
In order to solve the lack of speed in the A6M1, the A6M2 with the 940hp
Nakajima Sakae 12 motor was designed, and
15 pre-production machines were dispatched to Hankow in China for operational
trials on 21 July 1940. Sixteen months before Pearl Harbour, the Zero
flew its first combat mission. Such was the superiority over the Chinese
fighters that the Chinese refused to fight. Only two Zeros were lost
to enemy activity in this period, shot down by anti- aircraft fire.
Mitsubishi built another 47 A6M2 Model 11 aircraft by November 1940
before introducing the Model 21, which incorporated folding wingtips.
Under the 'Model' designation system, a change in the first digit denoted
an airframe change, alteration of the second digit denoted an engine
change. Thus the Model 'two one' showed that it differed structurally
from the Model 'one one' but retained the same motor. The A6M2 Model
21 was the standard JNAF fighter at the time of the attack on Pearl
Harbour, 328 of this model being amongst the 521 naval fighters on board
the Japanese aircraft carriers at that time.
Further models of the A6M were introduced to overcome problems and design
limitations, and to try to keep the superiority that the type enjoyed
over contemporary Allied aircraft:
A6M3 Model 32: Engine change to 1130hp Sakae 21, and removal
of the folding wingtip section, giving a clipped wing. To retain the
centre of gravity position with the heavier engine, the latter was moved
back towards the bulkhead. This reduced the fuel tank volume thus reducing
the combat radius.
A6M3 Model 22: Adding the original folding-tip wing to the Model
32 engine/body combination, and incorporating a 12 gallon fuel tank
in each wing in an attempt to reclaim lost range. By the time the Model
22 reached production, the Model 52 was approaching operational status;
thus the Model 22, appearing in combat after the Model 32, had a short
operational life. 560 were built late 1942 and early 1943 (this figure
is thought to include Nakajima production).
A6M5 Model 52: Similar to the Model 32, but with some weight
saving measures in the wing structure, heavier gauge wing skins to allow
higher dive speed, individual exhaust stacks for additional thrust.
The most numerous and widely used version of the Zero.
By the time that the Model 52 became outdated - 1944 - further modifications
of the basic design began to display an air of desperation. New designs
such as the A7M Reppu, J2M Raiden and N1K Shiden could not be debugged
or produced in sufficient volume, so the Zero had to soldier on. The
A6M4 (turbo-supercharged engine) A6M6 {water-methanol injection) A6M7
(fighter-bomber version) A6M8 (1350hp Kinsei engine) were all built
in varying quantities, but against the American Wildcat, Hellcat and
Corsair carrier-based fighters they and their inexperienced pilots had
little chance of success. By the end of the war more Zero fighters had
been built by Japan than any other type of aircraft. Mitsubishi had
produced 3879, but the majority were constructed by Nakajima who assembled
6215. Added to this were 844 trainers and floatplanes for a total of
10938 aircraft. After the cessation of hostilities a few Zeros flew
briefly for evaluation in some Allied air forces, and for a short while
longer in Indo-China and Indonesia.
|