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.

19 Comments | Add New

By Johnny .45  |  2010-07-17 at 21:25  |  permalink

So, I’m always curious when I find something like this, where the text is just about exactly verbatim from what’s in the Wikipedia article…did someone take THIS text and put it in Wikipedia, or did the author of this page take the text from Wikipedia?
In any case, the pictures and photos are useful. I’d still like to find out more about the US versions of the gun. Does anyone have any numbers that show exactly what they mean by “very unreliable”? I mean, they DID use the M2 Hispanos in planes like the P-61 Black Widow, so presumably they worked at least adequately.
If anyone knows a source that has any more info than this one does about US Hispanos, I’d appreciate it a lot. I can’t find much at all on them.
Johnny

By Petter Bøckman  |  2012-08-15 at 20:43  |  permalink

As the main author of the Wikipedia article, I can tell you the text was written for Wikipedia, and then copied (and changed a bit) here. The Wikipedia article is written under an open license, the use here is quite all right.

By Rude Håkansson  |  2010-07-18 at 18:57  |  permalink

Nice to see how the cannons are placed in the wings, nice fotos and very good for reference. Hard to find is some reference of the ammo, but i have some ww2, 20mm british live rounds on my homesite and also linked live 303 BR.

By T.Bailey  |  2011-04-04 at 18:31  |  permalink

The 20mm feeder pictured as fitted to the cannon in your photo was not electrically driven. The feeder springs inside the feeder were re-tensioned every time the gun recoiled. I am an ex Halton apprentice who worked on these guns during my training, and afterwards, during my service. Had many a fraught moment refitting those bloody springs to the feeder unit after servicing !! LOL

By Editor  |  2011-04-06 at 09:00  |  permalink

@T Bailey: Thank you very much for clarifying this, I will adjust the article accordingly. Much appreciated. /Martin

By Peter Haller  |  2011-12-31 at 15:58  |  permalink

As far as I know,Birkigt (the Swiss in Hispano-Suiza (Spanish/Swiss) designed the 404 himself in Geneva,after disagreement over licence-built oerlikons.A 1960s British aviation mag. wrote that in mid-war Birkigt went from Geneva to the Midlands (presumably via Lisbon boat or BOAC/KLM DC-3) in order to help with production snags caused ostensibly by conversion of Metric,Whitworth etc norms by wartime factories.
Pity there’s no real Birkigt biography-might have to do it myself ph

By Editor  |  2012-01-05 at 12:45  |  permalink

@Peter,

Thank you for this very valid comment. I had no idea that the Brits brought over the Swiss constructor of the Hispano cannon during the war. Very interesting.

Should you ever put the Birkigt biography in writing, I’d me more than happy to post it for the benefit of all our visitors.

/M.

By stan D  |  2012-02-09 at 02:50  |  permalink

The cannon as fitted in the spitfires was gas operated. The breach block was recoiled by an unlocking bar fitted on top of the barrel which automaticaly rewound the belt feed mechanism and reloaded a new round into the breach The 20 mm rounds were on a belt, held together by spring clips which were detached by the BFM.and ejected under tthe wing.

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