HS.404 in the TCM-20 twin anti-aircraft configuration, displayed at the Israeli Air Force Museum.
|Place of origin||France|
|Wars||World War II|
|Barrel length||80 calibres|
|Rate of fire||700 rounds/min|
|Muzzle velocity||880 m/s|
|Feed system||Drum magazine|
|Place of origin||United Kingdom|
|Used by||United Kingdom, Commonwealth & United States|
|Wars||World War II, Korean War|
|Rate of fire||750 rounds/min|
|Muzzle velocity||840 m/s|
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 caliber 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.
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. The firm was first organized in France in 1904 as a branch of Spanish La Cuadra automobile firm, formed by artillery captain Emilio de la Cuadra. It was later joined by Swiss engineer Marc Birkigt.
In the 1930s Hispano-Suiza took out a license on the Swiss Oerlikon MG FF 20 mm cannon, which they referred to as the "Hispano-Suiza Automatic Cannon Type HS.7" and HS.9. The MG FF, like all pre-war Oerlikon guns, was a recoil-operated weapon with certain unique features; a barrel that does not recoil and 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, Birkigt began work on the design of an entirely new design based on a locking mechanism patented in 1919 by Carl Swebilius (an American machine-gun inventor). The result was the Type 404, or HS.404, which was widely considered the best aircraft cannon of its kind. The HS.404 was gas-operated. When the projectile passes a port cut into the barrel, the hot gasses enters a chamber where it presses against a piston. The piston is connected to a rod that unlocks the bolt, allowing pressure in the barrel to drive the bolt backward. Since the bolt was locked during firing, the heavy bolt of the Oerlikon could be replaced by a much lighter one, which greatly increased the rate of fire, about 200 rounds a minute over the Oerlikon.
In 1938 Birkigt patented it and started production in their Geneva factory. 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 they referred to as a moteur-canon. The HS.404 was fed by drum magazines that could accommodate 60 rounds at most. 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 use was in 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-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 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 than and had 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.
United Kingdom & Commonwealth
- Hispano Mk. I
- Gloster F.9/37—a design not taken into service
- Westland Whirlwind—the RAF's first cannon-armed fighter.
- Bristol Beaufighter—early aircraft
- Hispano Mk. II
- Blackburn Firebrand
- Blackburn Firecrest
- Bristol Beaufighter
- CAC Boomerang
- Consolidated Liberator GR I (4 guns on 20 aircraft)
- de Havilland Mosquito
- Douglas Boston III (Intruder)
- Fairey Firefly
- Gloster Meteor
- Hawker Hurricane Mk IIC
- Hawker Tempest Mk V Srs I
- Hawker Typhoon Mk IB
- North American Mustang IA
- Supermarine Spitfire Marks V to Mark 20
- Hispano Mk. V
- Avro Lincoln (when fitted with mid-upper turrets)
- Avro Shackleton 
- Bristol Brigand
- de Havilland Hornet & Sea Hornet
- de Havilland Vampire
- de Havilland Venom & Sea Venom
- English Electric Canberra B.Mk.6 & B(I).Mk.8
- Hawker Fury & Sea Fury
- Hawker Sea Hawk
- Hawker Tempest Mk V Srs II and subsequent Marks
- Martin-Baker MB 5—prototype
- Saunders-Roe SR.A/1
- Supermarine Attacker
- Supermarine Seafang
- Supermarine Spiteful
- Supermarine Spitfire—Marks 21 and later
- Westland Welkin
- Westland Wyvern
- Bell P-400 (P-39 Airacobra diverted from export)
- Boeing B-29 Superfortress
- Douglas A-1 Skyraider
- Lockheed P-38 Lightning
- Northrop P-61 Black Widow
- Chance Vought F4U-1C Corsair
- Chance Vought F4U-4B Corsair and all following versions
- Chance Vought F6U Pirate
- Chance Vought F7U Cutlass
- Hispano Mk. V
- Hispano Mk. II
- 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
- Ammunition: 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
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- The Machine Gun, History, Evolution, and Development of Manual, Automatic, and Airborne Repeating Weapons. 1951 by George M. Chin, Lieutenant Colonel USMC. Prepared for the Bureau of Ordnance Department of the Navy.
- RCAF.com The Aircraft
- "Wartime British Remotely Controlled Guns and Turrets". 2003-05-09. Retrieved 2008-08-05.