The
Hispano-Suiza HS.404
was an autocannon widely used as both an
aircraft and land weapon in the 20th century by British
, American
, French
, the
Swiss Army and numerous other military
services. Firing a 20 mm diameter projectile, it
delivered a useful load of explosive from a relatively light
weapon. This made it an ideal aircraft weapon, replacing the
multiple 7.62 mm (.30 caliber)
machine
guns commonly used in military aircraft in the 1930s.
Development
The French company,
Hispano-Suiza S.
A., located in Bois Colombes, France, emerged from World War I as
one of the most famous aircraft engine manufacturers in the World.
This firm
was first organized in 1904 as a branch of the manufacturing firm
of automobiles in Spain, by a Spanish artillery captain Emilio de la Cuadraa (started with
electric automobile production in Barcelona
under the name of La Cuadra) and
was later joined by the Swiss engineer, Marc Birkigt. (hence the name
Hispano-Suiza).
In the 1930s, Hispano-Suiza manufactured, under Oerlikon license
the Swiss
Oerlikon FF,
MG FF, under the designation Hispano-Suiza Automatic
Cannon Type HS.7 and HS.9. The MG FF, like all Pre-War Oerlikon
guns a
recoil-operated weapon,
embodies certain features which are not found in other automatic
cannons; the most important of these are: a barrel which does not
recoil; a heavy breechblock which is never locked against the
breech and actually moves forward when the gun is fired.
Shortly after production began, the Hispano and Oerlikon Companies
disagreed over patent rights and their business connection came to
an end.
In 1933, Marc Birkigt, began work on the design of an entirely new
construction based on a locking mechanism patented in 1919 by Carl
Swebilius (an American machine-gun inventor). The weapon had been
designed for engine installation, since Hispano-Suiza was the
original promoter of this system of mounting. The result was the
Type 404, or HS.404, which was widely considered the best aircraft
cannon of its kind. In 1938 Birkigt patented it and produced it
successfully in his Swiss factory in Geneva, Switzerland.
The HS 404 was
gas-operated. When the
projectile passes the port in the barrel, the gas gives the piston
and the bolt extension a backward movement. This unlocks and
releases the clamped down locking piece, thus unlocking the bolt.
The gun’s main functional features were both gas power and
blow-back. With this system the breech was completely blocked as
long as the projectile was in the cannon. It not only ensured
safety but also allowed the use of a light bolt. As a result, a
rate of an additional 200 rounds a minute over the Oerlikon was
achieved.
The 404 was widely used on pre-war French designs, notably in
installations firing through the drive shaft of the
Hispano-Suiza 12Y engine, a system known
as a
moteur-canon. The HS.404 was fed by drum magazines
that could accommodate at most 60 rounds. Since in most
installations the magazine could not be switched during flight, the
small ammunition capacity was problematic. In 1940, Hispano-Suiza
was developing a belt-feeding system, as well as derivatives of the
HS.404 in heavier calibres such as 23 mm, but all these
projects were halted with the German occupation of France.
In the meantime, Great Britain had acquired a license to build the
HS.404, which entered production as the
Hispano
Mk.I. Its first used was with the
Westland Whirlwind of 1940,
providing the
Royal Air Force with a
powerful cannon-armed interceptor. It was also used in early
versions of the
Bristol
Beaufighter. The Beaufighter highlighted the need for a belt
feed mechanism; in the
night fighter
role the 60-round drums needed to be replaced in the dark by the
Wireless Operator, often while the aircraft
was maneuvering to keep sight of its quarry. In addition, early
trial installations in the
Hawker
Hurricane and
Supermarine
Spitfire had shown a tendency for the gun to jam during combat
maneuvers, leading to some official doubt as to the suitability of
cannons as the sole main armament. This led, briefly, to the
Air Ministry specifying 12-gun machine
gun armament for its future fighters.
Subsequently a suitable belt-feeding system was developed by the
Martin-Baker Aircraft Co. Ltd. and the new design was adopted by the
RAF and
FAA in 1941 in a slightly modified form as the
Hispano Mk.II. Four cannons replaced the eight
Browning .303
machine guns in the Hurricane and in
tropical versions of the Spitfire, and became standard armament in
later fighters. Most other Spitfires had only two cannons, because
of technical difficulties (i.e., inadequate gun-heating capacity
for the outboard cannon leading to the gun freezing at high
altitudes), along with four 0.303 calibre or two 0.50 calibre
machine guns.
The gun was also licensed for use in the United States as the
M1, with both the
United States Army Air Corps
(USAAC) and
U.S. Navy planning to switch to the 20 mm
as soon as sufficient production was ready. A massive building
program was set up, along with production of
ammunition, in 1941. When delivered, the guns
proved to be extremely unreliable and suffered a considerable
number of misfires due to the round being "lightly struck" by the
firing pin. The British were interested
in using this weapon to ease production in England, but after
receiving the M1 they were disappointed.
In April 1942 a copy of the British Mk.II was sent to the U.S. for
comparison, the British version used a slightly shorter
chamber and did not have the same
problems as the U.S. version of the cannon. The U.S. declined to
modify the chamber of their version, but nevertheless made other
modifications to create the no-more-reliable
M2.
By late 1942 the USAAC had 40 million rounds of ammunition stored,
but the guns remained unsuitable. The U.S. Navy had been trying to
go all-cannon throughout the war, but the conversion never
occurred. As late as December 1945 the
Army's Chief of Ordnance was still
attempting to complete additional changes to the design to allow it
to enter service.
Meanwhile, the British had given up on the U.S. versions and
production levels had been ramped up to the point where this was no
longer an issue anyway. They upgraded to the
Hispano
Mk. V, which had a shorter
barrel, was lighter and had a higher rate of
fire, (desirable in aircraft armament) although at the expense of
some muzzle velocity. One of the main British fighters to use the
Mk. V was the
Hawker Tempest Mk. V Series II, which mounted a total of four.
The U.S. followed suit with the
M3, but
reliability problems continued. After
World
War II the
United States Air
Force (USAF) adopted a version of the M3 cannon as the
M24, similar in most respects except for the use
of electrically primed ammunition.
The Hispano fired a 130 gram (4.58 oz) 20 mm × 110 mm
projectile with a
muzzle velocity
between 840 and 880 m/s (2,750 and 2,900 ft/s), depending on barrel
length. Rate of fire was between 600 and 850 rounds per minute. It
was 2.36 m (7 ft 9 in) long, weighing between 42 and 50 kg (93
and 110 lb). The British Mk V and American M3/M24 weapons were
lighter with higher rates of fire than the early HS.404 guns.
In the post-war era the HS.404 disappeared fairly quickly due to
the introduction of
revolver cannon
based on the German
Mauser MG 213. The
British introduced the powerful 30 mm
ADEN cannon in most of their post-war designs,
and the French used the very similar
DEFA
cannon, both firing the same ammunition. The USAF introduced
the 20 mm
M39 revolver cannon to replace the M24, while
the Navy instead combined the original Hispano design with a
lighter round for better muzzle velocity in the
Colt Mk 12 cannon.
Usage
France
- HS.404
United Kingdom & Commonwealth
- Hispano Mk. I
- Hispano Mk. II
Avro Shackleton, sporting two Hispano Mk.
- Hispano Mk. V
United States
- M1
- M2
- M3
- M24
Yugoslavia
- HS.404
Sweden
- Hispano Mk. V
Argentina
- Hispano Mk. II
Specifications HS.404
- Type: single-barrel automatic cannon
- Caliber: 20 mm × 110 (0.79 in)
- Operation: gas
operated
- Length without muzzle brake: 2.32 m
- Length with muzzle brake: 2.52 m
- Weight without drum magazine: 43 kg
- Weight (complete): 68.7 kg
- Rate of fire: 600–700 rpm
- Muzzle velocity: 840 to 880 m/s (2,750 to
2,900 ft/s)
- Recoil force: 400 kg with muzzle
brake
- Amunition: Ball, Incendiary, HE
(High-Explosive)
- Projectile weight: 130 g HE and HEI 168 g
AP-T
- HE and HEI rounds explosive filler: 6 - 11
g
See also
Notes
- RCAF.com The Aircraft
References
- The Machine Gun, History, Evolution, and Development of
Manual, Automatic, and Airborne Repeating Weapons. 1951 by
George M. Chinn, Lieutenant Colonel USMC. Prepared for the Bureau
of Ordnance Departement of the Navy.
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