The Hispano Cannon

Spitfire Site

The Hispano cannon was one of the most widespread aircraft weapons of the war, and one which gave the Spitfire its punch.

British Hispano Mk. II cannon (to the left) exposed.
[Martin Waligorski]

The Hispano-Suiza HS.404 20 mm-calibre automatic cannon was one of the most widespread aircraft weapons of the 20th century, used by British, American, French, and many 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 cannon for use onboard fighters, replacing the multiple 7.62 mm (.30 caliber) machine guns commonly used in military aircraft in the 1930s.

Overall arrangement of the armament bay of the Spitfire LF Mk. IXe, with Hispano Mk. II cannon to the left and the American M2 Browning machine gun to the right.
[Martin Waligorski]

Development

Like the name implies, the Hispano cannon was developed by the French company Hispano-Suiza. It was based on the earlier Swiss Oerlikon FF S weapons, which the company manufactured under license in France as HS.7 and HS.9.

In the late 1930s, engineer Marc Birkigt designed a new and much improved version with a revised action, much faster rate of fire, and somewhat higher muzzle velocity. The result was the Type 404, or HS.404, which was widely considered the best aircraft cannon of its kind. 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 employed in Morane-Saulnier M.S.406 and Dewoitine D.520.

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.

British License

In the meantime, Great Britain had acquired a license to build the HS.404, which was first used in a British fighter as the Hispano Mk.I with the Westland Whirlwind of 1940. British engineers developed a belt-feeding mechanism. The new design was adopted by the RAF and FAA in 1941 in a slightly modified form as the Hispano Mk.II.

Four cannon replaced the eight Browning .303 machine guns in the Hawker Hurricane Mk. IIc and in Supermarine Spitfire Mk. Vc, and became standard armament in late-war British fighters such as the Hawker Typhoon/Tempest family or late marks of the Spitifre. Although earlier Spitfires equipped with Type C wing could accomodate four cannon, most of them carried only two because of technical difficulties such as inadequate gun-heating capacity for the outboard cannon leading to the gun freezing at high altitiudes.

Installation of Mk. II Hispano cannon in the wing of Spitfire Mk. Vc.
[Crown Copyright]

American License

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, with the differences being primarily that the British version used a slightly shorter chamber that they believed was the cause of the U.S.’s problems.

The U.S. declined to modify the chamber of their version, but nevertheless made other different 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.

Hispano Mk. V

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, 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.

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 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.

A pair of Mk. V Hispanos installed in the wing of the Spitfire Mk. 21. Shorter barrels and smaller feed motors resulted in a more compact arrangement.
[Crown Copyright]

Specifications

The Mk. II Hispano fired a 130 gram (4.58 oz) 20 mm x 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.

  • Type: single-barrel automatic cannon
  • Calibre: 20 mm ?110 (0.79 in)
  • Operation: gas operated
  • Length: 2.36 m (7 ft 9 in)
  • Weight (complete): 42?50 kg (93?110 lb)
  • Rate of fire: 600?850 rpm
  • Muzzle velocity: 840 to 880 m/s (2,750 to 2,900 ft/s)
  • Projectile weight: 130 g (4.58 oz)
  • HE round explosive filler: ~6 g

Installation of the Hispano Mk. II in the armament bay of the Spitfire LF Mk. IXe. The prominent drum on top of the cannon breech is the belt-feeder, a spring-loaded mechanism which was re-tensioned every time the gun recoiled.The smaller breech to the right of the cannon belongs to the .5″ M2 Browning machine gun.
[Martin Waligorski]

Details of the belt-fed Hispano Mk.II installation in the armament bay of the Spitfire LF Mk. IX, looking aft. The belt was pulled from the ammunition box, integrated with the wing’s structure, through a roller visible at the right edge of the photo.
[Martin Waligorski]

The text in this article uses content from a Wikipedia article and is therefore  licensed under the GNU Free Documentation License (GFDL). The Images are property of their respective copyright owners as specified and are not sin the GFDL unless specifically stated.

12 Comments | Add New

By caryn  |  2012-08-24 at 14:19  |  permalink

A couple of things:

As far as the RAF/FAA gun fit, one of the principal reasons the .303 Brownings were retained for so long was ammunition capacity.

I’m not certain what you mean by the M24 and “electrically primed ammunition”; the M24 fired standard 20×110 rimless (USN) cartridges, with impact primers. The cannon were electrically charged (or “cocked”, sometimes called “primed” in US nomenclature) and electrically fired (via solenoid), but the ammunition was entirely conventional?

By Carl Foley  |  2012-12-16 at 23:55  |  permalink

Not all 20 mm hispano were electrically cocked. RNZAF Vampires had those weapons and they were cocked by the armourer not long before the aircraft were to take off. The ammunition was in place as was the BFM (belt feed mechanism), but the breech block was still forward in the breech (and therefore the gun was totally safe) . The armourers used a lanyard thingy over a little wheel to pull the breech block rearward where it remained ready until the gun was fired, whereupon it moved forward and collected a round from the BFM on its way.

By John Ely  |  2013-09-30 at 12:17  |  permalink

Carl,

I was Royal Canadian Air Force Armourer for 25 years. In my younger years I worked on the CF-5 Load Crews and had the pleasure off cocking the “Charger” to load ar and de-arm.

Questio is do you know how much force it took to pull the charging handle a fully rotate the drum?

Cheers

John

By Monty Quick  |  2013-05-23 at 10:39  |  permalink

I have a MK.V Hispano 20mm cannon serial number 608 and wondered how I could find out what aircraft it came from? Any ideas?
Regards
Monty

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