Hispano-Suiza HS.404

HS.404
HS.404 in the TCM-20 twin anti-aircraft configuration, displayed at the Israeli Air Force Museum.
Type	Aircraft cannon
Place of origin	France
Service history
Wars	World War II Korean War
Production history
Designer	Marc Birkigt
Manufacturer	Hispano-Suiza
Specifications
Weight	43 kg (94 lb 13 oz)
Length	2.52 m (8 ft 3 in)
Barrel length	80 calibres
Cartridge	20×110mm
Caliber	20 mm (0.79 in)
Action	Gas operated, delayed blowback
Rate of fire	700 rounds/min
Muzzle velocity	880 m/s (2,900 ft/s)
Feed system	Drum magazine, belt (later models)

20mm M1 Automatic Gun
Type	Aircraft cannon
Place of origin	United States
Service history
In service	United States Army Air Force
Used by	United States
Wars	World War II Korean War
Production history
Manufacturer	International Harvester
Produced	1941 – April 1942
Variants	A/N M2, A/N M3, M24
Specifications
Weight	64.5 lb (29.3 kg) (breech mechanism) 47.5 lb (21.5 kg) (barrel with Muzzle Brake) 22 lb (10.0 kg) (loaded 60-round M1 drum magazine) 19 lb (8.6 kg) (M1 Feed Mechanism).
Length	100.6 in (2.56 m)
Barrel length	67.5 in (1,710 mm) Rifling: 9 grooves, right-hand twist, 1-in-63 inches (1:160 cm) turn.
Cartridge	20×110mm Hispano "A"
Calibre	20 mm (0.79 in)
Action	Gas operated, delayed blowback
Rate of fire	600–700 rounds/min
Muzzle velocity	2,850 ft/s (870 m/s)
Maximum firing range	7,000 yards
Feed system	60-round M1 drum or linked belt

Hispano Mk.V
Type	Aircraft cannon
Place of origin	United Kingdom
Service history
Used by	United Kingdom & the British Empire, Commonwealth, United States
Wars	World War II Korean War
Specifications
Weight	42 kg (92 lb 10 oz)
Cartridge	20×110mm
Calibre	20 mm (0.79 in)
Action	Gas operated, delayed blowback
Rate of fire	750 rounds/min
Muzzle velocity	840 m/s (2,800 ft/s)
Feed system	Belt

The HS.404 was an autocannon produced by Hispano-Suiza and derivates and was widely used as both an aircraft and land based weapon in the 20th century by French, British, American and numerous other military services, particularly during the Second World War. The cannon is also referred to as Birkigt type 404, after its designer Marc Birkigt, and later versions based on British development are known as 20mm Hispano. Firing a 20 mm caliber projectile, it delivered a useful load of explosive from a relatively light weapon. This made it an ideal anti-aircraft weapon for mounting on light vehicles, as well as a fighter aircraft gun, replacing the multiple 7.62 mm (.30 caliber) and .303 inch (7.7 mm) machine guns commonly used in military aircraft of the 1930s. The HS.404 was produced by the French subsidiary of Hispano-Suiza.

Development

From Oerlikon to Hispano

In the 1930s, Hispano Suiza S.A. was licensed to build an engine drive shaft version of the Swiss Oerlikon FF S or Becker model, an advanced primer ignition blowback design, firing from an open bolt. The Oerlikon FF S was based on the Oerlikon 20 mm anti-aircraft auto-cannon. The Hispano-Suiza version was called the "Hispano-Suiza Automatic Cannon Type HS.7" and HS.9. The Swiss cannon, like all pre-war Oerlikon guns, was a blowback 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-Suiza and Oerlikon companies disagreed over patent rights and their business connection came to an end.

In 1933, the chief engineer of Hispano-Suiza, Marc Birkigt, began work on the design of an entirely new weapon to replace the Oerlikon contract, based on a locking mechanism patented in 1919 by the American machine-gun designer Carl Swebilius. The result was the Type 404, or HS.404. While the HS.404 resembled the parent Oerlikon FF S in many respects, its repeating mechanism was gas-operated. When the projectile passes a port cut into the barrel, hot gas behind the projectile is siphoned off and enters a chamber. There it pressed against a piston. The piston is connected to a rod that unlocks the bolt, allowing the gas 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 to 700 rounds per minute (rpm), about 200 rpm greater than the Oerlikon. In 1938, Birkigt patented it and started production in their Geneva factory.

Oerlikon also continued development of their design through this period with an eye to improving rate of fire. They retained the original blowback concept with its heavy bolt, choosing to improve cycle time by lowering the amount of gunpowder in the shell, which also had the effect of reducing the muzzle velocity. These changes produced the MG FF, which was widely used on WWII German aircraft especially in the first half of WWII. In spite of these changes, the HS.404 retained a firing rate advantage over the Oerlikon designs throughout the war.

Anti-aircraft gun

Israeli anti-aircraft M3 Half-track with twin H.S. 404 auto-cannons

The HS.404's predecessor, the Oerlikon auto-cannon, was rather heavy and the movement of the heavy bolt made it best suited in static and maritime anti-aircraft defence. In contrast the lighter bolt of the HS.404 made it well suited to mounting on vehicles. The M16, an anti-aircraft version of the M3 Half-track, could be equipped with single or double American made copies of the Hispano-Suiza auto-cannon. This variant of the M3 Half-track was used by US and Commonwealth forces late in the Second World War and in the Korean War and was further developed by Israel in the post-war era.

Aircraft gun

In 1938, an aircraft based version of the HS.404 was produced at the request of the French government. It was installed on a wide range of pre-war French fighter plane designs, notably in installations firing through the drive shaft of the Hispano-Suiza 12Y engine, a system referred to as a moteur-canon ("engine cannon"). 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 a weakness. 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 these projects were halted with the German occupation of France.

British production

In the buildup to the Second World War, the United Kingdom had embarked on a programme to develop cannon-armed fighters. They acquired a licence to build the HS.404, which entered production as the Hispano Mk.I intended as aeroplane armament. Its first use was in the Westland Whirlwind of 1940, and later in the more powerful Bristol Beaufighter, providing the Royal Air Force with powerful cannon-armed interceptors. The experience of the Battle of Britain had shown the batteries of eight rifle-calibre machine guns to be inadequate and prompted the adoption of auto cannon armament for the primary portion of Royal Air Force (RAF) fighters. The Beaufighter highlighted the need for a belt feed mechanism; as a night fighter the 60-round drums needed to be replaced in the dark by the Radar/Wireless Operator, often while the aircraft was manoeuvering to keep sight of its quarry. In addition, the early trial installations in the Hawker Hurricane and Supermarine Spitfire had shown a tendency for the gun to jam during combat manoeuvres, leading to some official doubt as to the suitability of cannons as the sole main armament. This led to the Air Ministry for a brief period specifying 12-machine gun armament for new fighters.

Subsequently a suitable belt-feeding system was developed by Martin-Baker, and the new design was adopted by the RAF and Fleet Air Arm in 1941 in a slightly modified form as the Hispano Mk.II. Four cannons replaced the eight .303 Browning machine guns in the Hurricane and in some tropical versions of the Spitfire, becoming standard armament in later fighters. Most other Spitfires had only two cannons, because of technical difficulties (i.e., inadequate room for gun-heating capacity for the outboard cannon leading to the gun freezing at high altitudes), along with four 0.303 caliber (7.7mm) or two 0.50 caliber (12.7mm) machine guns.

The British were concerned their production would be inadequate and licensed production of the Hispano to the US. However, the US production never became satisfactory and the British eventually gave up on the U.S. versions. British production was eventually increased to the point where this was no longer an issue. The ultimate version of the British wartime Hispanos was the Hispano Mk. V, which had a shorter barrel, and lacked the cocking cylinder thus requiring manual cocking before flight. It was lighter and had a higher rate of fire (desirable in aircraft armament), although at the expense of some muzzle velocity. The shorter barrel meant that the weapon could be housed within the wing of a fighter plane, reducing drag and making them less vulnerable to freezing and mechanical stress. One of the main British fighters to use the Mk. V was the Hawker Tempest Mk. V Series II, which mounted two cannons in each wing. Ammunition types available included Semi-Armour Piercing, Incendiary (SAPI) and High Explosive, Incendiary (HEI).

US production

US Patent drawing of the Hispano Suiza cannon.

The British version 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 caliber as soon as the gun could be produced in sufficient numbers. A very large building program was established, 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 the demand on production in England, but after receiving the M1 they were disappointed. British wing-mounted fighter weapons by this period were cocked on the ground by the aircraft armourers before flight, the built-in pneumatic cocking mechanism used previously being regarded as unnecessary weight and detrimental to aircraft performance, so any stoppage in flight made the gun unusable until it could be cleared on the ground. The misfires also had the tendency to cause aircraft with wing-mounted guns to yaw towards the wing with the failed gun when the guns were fired, due to the unequal recoil, thus throwing-off the pilot's aim.

A lieutenant inspects an ammunition belt as used by the 20 mm Hispano cannon visible in the nose of a Lockheed P-38 Lightning.

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 nonetheless made other modifications to create the unreliable M2. By late 1942 the USAAF 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. Some variations of the 20 mm guns used on the Lockheed P-38 Lightning aircraft were produced by International Harvester. The P-38's nose-mounted M2 featured a built-in cocking system, and could simply be re-cocked in flight after a misfire, which made the misfires less of a problem than with other aircraft.

The U.S. followed the British development closely and when the Mk.V was designed, the Americans followed suit with the A/N M3 but unreliability 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 the addition of electrical cocking, allowing the gun to re-cock over a lightly struck round. The problems of the American weapons led to most US fighters being equipped with the AN/M2 .50 cal Browning light-barrel HMG throughout the war.

Post-war development

After the war the Hispano variants disappeared fairly quickly as fighter armament due to the introduction of revolver cannons, based on the prototype versions of the never-produced German wartime Mauser MG 213 cannon. The British introduced the powerful revolving 30 mm caliber ADEN cannon in most of their post-war designs, while the French used the very similar DEFA cannon, firing similar ammunition. Similarly, the USAF introduced the 20 mm M39 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. As a ground vehicle mounted gun, either anti-aircraft or as a general-purpose autocannon, the HS.404 lasted into the 1960s. A powered turret variant is still in production in Honduras, and is used as a light anti-aircraft gun by the army and navy in several nations. The A/N M3 was developed into the Mk16 Colt 20mm automatic cannon, one of the main weapons on boats of the Mobile Riverine Force in the Vietnam War and also used on some larger amphibious ships.

Properties

The Hispano fired a 130 g (4.586 oz) 20 mm diameter projectile from a 110 mm (4.331 in) long casing, the whole round weighing 257 g (9.065 oz). Lengths of the projectiles varied with type, but were set to variable depth in the casing to produce a total full round length of 184 mm (7.244 in) regardless of projectile type. The gun had a muzzle velocity between 840 and 880 m/s (2,800 and 2,900 ft/s), depending on barrel length. Rate of fire was between 600 and 850 rounds per minute. The gun 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 and had higher rates of fire than the early HS.404 guns.

Users

France

Morane-Saulnier M.S.406, one of several French fighters with the moteur-canon firing through the drive shaft.

• HS.404
  • Bloch MB.152
  • Breguet 693
  • Dewoitine D.500
  • Dewoitine D.520
  • Lioré et Olivier LeO 45
  • Morane-Saulnier M.S.406
  • Potez 631

United Kingdom & British Empire

• 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

Hawker Hurricane Mk.IV with the long barrels of the Mk.II Hispanos in the wings

A Mustang Mk.IA, the only version of the Mustang to carry autocannons: the Hispano Mk.II

• Hispano Mk. II
  • Blackburn Firebrand
  • Blackburn Firecrest
  • Bristol Beaufighter
  • CAC Boomerang
  • Consolidated Liberator I (4 guns on 20 aircraft)
  • de Havilland Mosquito
  • Douglas Boston III (Intruder)
  • Fairey Firefly
  • Gloster Meteor
  • Hawker Hurricane Mk IIC and IV
  • Hawker Tempest Mk V Srs I
  • Hawker Typhoon Mk IB
  • Martin-Baker MB 3—prototype
  • North American Mustang IA
  • Supermarine Spitfire Marks V to Mark 20

Avro Shackleton, sporting two Hispano Mk. V in the nose

The short barrel Mk.V was used in most early British jet fighters, like this Vampire. The gun ports are visible on the underside of the nose

• Hispano Mk. V
  • Aérospatiale Alouette III (South African Air Force cabin mounted)
  • Avro Lincoln (when fitted with mid-upper turrets)
  • Avro Shackleton
  • Bristol Brigand
  • de Havilland Hornet & Sea Hornet
  • de Havilland Vampire
  • de Havilland Venom & de Havilland 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

United States

Twin M3 barrels poking out from the leading edges of the wings of a Corsair.

• M1
  • Bell P-39 Airacobra - some early 20mm-armed models and RAF Bell Airacobra I
  • Lockheed P-38 Lightning - some early 20mm-armed models and RAF Lockheed Lightning I

• A/N-M2
  • Bell P-400 (P-39 Airacobra diverted from export)
  • Boeing B-29 Superfortress - In tail turret with two 0.5 in machine guns
  • Douglas A-1 Skyraider
  • Douglas F3D Skyknight
  • Grumman F9F Panther
  • Grumman F-9 Cougar
  • Lockheed P-38 Lightning
  • Northrop P-61 Black Widow
  • Chance Vought F4U-1C Corsair

• T31
  • Douglas A2D Skyshark

• M3
  • Chance Vought F4U-4B Corsair and all following versions
  • Chance Vought F6U Pirate
  • Chance Vought F7U Cutlass
  • Douglas A-3 Skywarrior
  • Grumman F9F Panther
  • Grumman F8F Bearcat - used M3's from the F8F-1B on
  • Grumman F-9 Cougar

• M24
  • Convair B-36
  • Boeing B-47 Stratojet
  • Douglas B-66 Destroyer
  • Northrop F-89C Scorpion

Yugoslavia

• HS.404
  • Ikarus IK-2
  • Rogožarski IK-3

Sweden

• Hispano Mk. V Aircraft
  • Saab 29 Tunnan
  • Saab 32 Lansen

• Hispano Mk. V Armoured Vehicles
  • Pansarbandvagn 302 The vehicle used cannons from scrapped Saab 29 aircraft and mounted them on the 302 Armoured Vehicle.
  • Pansarterrängbil 203A As with the 302, the 203A use a single 20 mm cannon from scrapped Saab 29 aircraft.

Argentina

• Hispano Mk. II
  • I.Ae. 24 Calquin

• Hispano Mk. V
  • I.Ae. 30 Ñancú
  • FMA IAe 33 Pulqui II

Specifications HS.404

• Type: single-barrel automatic cannon
• Caliber: 20 mm × 110 (0.79 in)
• Operation: gas operated, delayed blowback
• Length without muzzle brake: 2.32 m (7 ft 7 in)
• Length with muzzle brake: 2.52 m (8 ft 3 in)
• Weight without drum magazine: 43 kg (94 lb 13 oz)
• Weight (complete): 68.7 kg (151 lb 7 oz)
• Rate of fire: 600–700 rpm
• Muzzle velocity: 840 to 880 m/s (2,800 to 2,900 ft/s)
• Recoil force: 400 kg (881.849 lb) with muzzle brake
• Ammunition: Ball, Incendiary, HE (High Explosive)
• Projectile weight: HE and HEI: 130 g (4.6 oz), AP-T: 168 g (5.9 oz)
• HE and HEI rounds explosive filler: 6 to 11 g (0.21 to 0.39 oz)

Ammunition

US

World War II

Ammunition was shipped in rectangular 10-shell fiberboard cartons. There were 12 cartons per metal-lined wooden packing crate (120 rounds).

• 20mm Ball Mk. I
  • Weight (Projectile): 0.28 lb (0.13 kg)
  • Weight (Complete Round):0.56 lb (0.25 kg) each.
  • Weight (Packing Crate):93.6 lb (42.5 kg).
  • Volume (Packing Crate): 1.45 Cubic Feet.
• 20mm High Explosive - Incendiary Mk. I
  • Fuze: No.253 Mk.IA Direct Action (Percussion) Fuze.
  • Weight (Projectile): 0.29 lb (0.13 kg)
  • Weight (Payload): 0.03 lb (0.014 kg) of high explosive and incendiary fillers.
  • Weight (Complete Round):0.57 lb (0.26 kg) each.
  • Weight (Packing Crate): 94.8 lb (43.0 kg).
  • Volume (Packing Crate): 1.45 Cubic Feet.
• 20mm Armor Piercing - Tracer M75
  • Weight (Projectile): 0.37 lb (0.17 kg)
  • Weight (Complete Round):0.64 lb (0.29 kg) each.
  • Weight (Packing Crate): 103 lb (47 kg).
  • Volume (Packing Crate): 1.45 Cubic Feet.

Post-War

The M90 series of shells were ballistically matched to make it easier to use different types without losing accuracy. Ammunition was shipped in 25-round metal canisters. There were 6 metal canisters per wooden crate (150 rounds).

• 20mm Drill M18A2
  • Weight (Projectile): ?
  • Weight (Complete Round): ? each.
  • Weight (Packing Crate): ?
  • Volume (Packing Crate): 1.5 Cubic Feet.
• 20mm HEFI_SAP M18A2
• 20mm Armor Piercing - Tracer M95 (T9E5)
  • Weight (Projectile): 0.29 lb (0.13 kg)
  • Weight (Complete Round):0.57 lb (0.26 kg) each.
  • Weight (Packing Crate):106 lb (48 kg).
  • Volume (Packing Crate): 1.5 Cubic Feet.
• 20mm Incendiary M96 (T18)
  • Weight (Projectile): 0.27 lb (0.12 kg)
  • Weight (Complete Round):0.55 lb (0.25 kg) each.
  • Weight (Packing Crate):103 lb (47 kg).
  • Volume (Packing Crate): 1.5 Cubic Feet.
• 20mm High Explosive - Incendiary M97 (T23)
  • Weight (Projectile): 0.29 lb (0.13 kg)
  • Weight (Complete Round):0.57 lb (0.26 kg) each.
  • Weight (Packing Crate):106 lb (48 kg).
  • Volume (Packing Crate): 1.5 Cubic Feet.
• 20mm Training-Practice M99 (T24)
  • Weight (Projectile): 0.29 lb (0.13 kg)
  • Weight (Complete Round):0.57 lb (0.26 kg) each.
  • Weight (Packing Crate):106 lb (48 kg).
  • Volume (Packing Crate): 1.5 Cubic Feet.

See also

• Hispano-Suiza HS.820
• MG FF cannon
• ShVAK cannon

References

• War Department Training Manual TM 9-227 20mm M1 Automatic Gun & 20mm AN-M2 Automatic Gun (November 19, 1942).

External links

• The short film STAFF FILM REPORT 66-19A (1966) is available for free download at the Internet Archive.