Hispano-Suiza HS.404

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, and numerous other military services. The cannon is also referred to as Birkigt type 404, after its designer. 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 in the 1930s.

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 Swiss 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, about 200 rounds over the Oerlikon. In 1938, Birkigt patented it and started production in their Geneva factory. In the comparable MG FF — a Swiss development of the Oerlikon—the mechanism remained an advanced primer ignition blowback, and lightening of the bolt was only achieved by a lighter charge, which also lowered muzzle velocity. Still, the Hispano retained its advantage in rate of fire throughout the war compared to the MG FF.

Aircraft and anti-aircraft gun


The HS.404 was widely used on pre-war French fighter plane designs, notably in installations firing through the drive shaft of the Hispano-Suiza 12Y engine, a system they 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.

The new auto cannon was not only considered the best aircraft cannon of its kind but was also suited for anti-aircraft use. While the predecessor Oerlikon auto-cannon, was rather heavy and the movement of the heavy bolt made it best suited in static and maritime anti-aircraft defence, the HS.404 was 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 Korean War and was further developed by Israel in the post-war era.

British production
In the buildup to the Second World War, the United Kingdom had embarked on a programme to develop cannon-armed fighters and 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 manouvres, 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 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 together with the deletion of the cocking cylinder thus requiring manual cocking before flight, 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


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 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. 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.



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 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. Some variations of the 20 mm guns used on the Lockheed P-38 Lightning aircraft were produced by International Harvester.

The U.S. followed the British development closely and when the Mk.V was designed, the Americans followed suit with the 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 electrically primed ammunition. 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 German wartime Mauser MG 213. 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.

Properties
The Hispano fired a 130 g 20 mm diameter projectile from a 110 mm long casing, the whole round weighing 257 g. Length of the projectiles vary with type, but are set to variable depth in the casing to produce a total full round length of 184 mm regardless of projectile type. The gun has a muzzle velocity between 840 to 880 m/s, depending on barrel length. Rate of fire was between 600 and 850 rounds per minute. It was 2.36 m long, weighing between 42 to 50 kg. The British Mk V and American M3/M24 weapons were lighter and had higher rates of fire than the early HS.404 guns.

France

 * 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




 * 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
 * North American Mustang IA
 * Supermarine Spitfire Marks V to Mark 20




 * 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

 * 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


 * 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 veichle 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

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
 * Recoil force: 400 kg with muzzle brake
 * Ammunition: Ball, Incendiary, HE (High Explosive)
 * Projectile weight: HE and HEI: 130 g, AP-T: 168 g
 * HE and HEI rounds explosive filler: 6 to 11 g

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
 * Weight (Complete Round):0.56 lb each.
 * Weight (Packing Crate):93.6 lb.
 * 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
 * Weight (Payload): 0.03 lb of high explosive and incendiary fillers.
 * Weight (Complete Round):0.57 lb each.
 * Weight (Packing Crate): 94.8 lb.
 * Volume (Packing Crate): 1.45 Cubic Feet.
 * 20mm Armor Piercing - Tracer M75
 * Weight (Projectile): 0.37 lb
 * Weight (Complete Round):0.64 lb each.
 * Weight (Packing Crate): 103 lb.
 * 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 Armor Piercing - Tracer M95 (T9E5)
 * Weight (Projectile): 0.29 lb
 * Weight (Complete Round):0.57 lb each.
 * Weight (Packing Crate):106 lb.
 * Volume (Packing Crate): 1.5 Cubic Feet.
 * 20mm Incendiary M96 (T18)
 * Weight (Projectile): 0.27 lb
 * Weight (Complete Round):0.55 lb each.
 * Weight (Packing Crate):103 lb.
 * Volume (Packing Crate): 1.5 Cubic Feet.
 * 20mm High Explosive - Incendiary M97 (T23)
 * Weight (Projectile): 0.29 lb
 * Weight (Complete Round):0.57 lb each.
 * Weight (Packing Crate):106 lb.
 * Volume (Packing Crate): 1.5 Cubic Feet.
 * 20mm Training-Practice M99 (T24)
 * Weight (Projectile): 0.29 lb
 * Weight (Complete Round):0.57 lb each.
 * Weight (Packing Crate):106 lb.
 * Volume (Packing Crate): 1.5 Cubic Feet.