# Why build the Oerlikon 20mm/70 light AA gun?



## davebender (Mar 14, 2012)

*HE Projectile Weight.*
130g. Hs.404
123g. Oerlikon 20mm/70

*Rate of fire.*
600 to 700 rpm. Hs.404
450 rpm. Oerlikon 20mm/70

*Muzzle Velocity.*
2,800 to 2,900 ft/sec. Hs.404
2,770 ft/sec. Oerlikon 20mm/70

*Weapon Weight.*
95 lbs. Hs.404
150 lbs. Oerlikon 20mm/70

It appears to me sustained fire before overheating was the only advantage of the Oerlikon 20mm/70 AA gun. Otherwise the Hs.404 20mm autocannon was superior in every way. 

The Hs.404 cannon was light enough that you could build a quad mount (similiar to flakvierling). Like the German weapon, only two barrels would fire at a time during sustained fire while the other two are cooling. That gives you 1,200 to 1,400 rpm sustained fire.

So why did Britain and the USA choose the Oerlikon 20mm/70 as their standard light AA weapon when they could have produced a variant of the Hs.404 autocannon?


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## Shortround6 (Mar 14, 2012)

Oh, just maybe the Oerlikon gun was cheaper (easier to produce) simpler to maintain, more reliable in maritime conditions.

There is no sustained fire for more than a few seconds with a ground/surface gun. The Oerlikons 60 round drum wil last 2 1/2 times longer than the German guns 20 round box. While 20mm barrles will last longer than .50 cal barrels "sustained" fire was not a real requirement.

By the way, at times the projectiles were interchangeable although the cartridge cases were not.


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## davebender (Mar 14, 2012)

Flakvierling were used primarily against ground targets. That's why the Heer used the very powerful 20mm x 138mm B cartridge while accepting a lower rate of fire.

Nothing prevents American and British light AA guns from being used against ground targets but I think AA capability drove weapons design. IMO the Hs.404 cannon would probably be superior for the light AA mission.


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## Shortround6 (Mar 14, 2012)

It wasn't. It was tried both on ships and on land. While the 60 round drums might not have been what was desired on either gun for multi aircraft attacks they were usually sufficient for a single aircraft which a 20 magazine was not. 

The Flakvierling came either after or while the Flak 38 was being adopted. Since the Flak 30 and the early 2cm AFV guns had already decided the ammo issue ( and the MG 151/20mm was a lousy AA round) the claim that the Heer designed the Flakvierling for use against ground targets seems a bit out of whack. Ground targets do not need multiple 20mm cannon barrels to defeat them. Some times handy to have nothing else is available an equal weight larger single barrel gun may be more effective.


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## tomo pauk (Mar 14, 2012)

I'd really like to see an Allied Flakvierling anyway, too bad Hispano copies were arranged in that layout only after the WW2, by Yugoslav Navy. The ready ammo load of 240 rounds seem to good to pass on it


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## davebender (Mar 14, 2012)

> Ground targets do not need multiple 20mm cannon barrels to defeat them


Otto Carius thought the flakvierling an excellent weapon for employment against ground targets. I have no reason not to believe him.


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## fastmongrel (Mar 14, 2012)

The Oerlikon used by the allies was a mature reliable gun when it was put into production. The HS 404 still had bugs maybe it was as simple as that. 4 barrel Oerlikons mounts were designed but lost the simple bolt down anywhere there was space attributes of the single and twin mounts.


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## davebender (Mar 14, 2012)

*Hispano-Suiza HS.404*
Hispano-Suiza HS.404 - Wikipedia, the free encyclopedia


> In 1938 Birkigt patented it and started production in their Geneva factory




*Oerlikon 20 mm/70 *
Britain, Switzerland and USA 20 mm/70 (0.79") Oerlikon Marks 1, 2, 3 and 4


> Oerlikon made the necessary changes and the first prototypes of the new design were delivered late in 1939.


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## tomo pauk (Mar 14, 2012)

Is it too far fetched that Hispano was RAF's favorite gun, while Oerlikon was Army and RN gun? Toss in some inter-service love and we could be near to the answer


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## fastmongrel (Mar 14, 2012)

The Oerlikon had been in production in various versions for several years before the Hispano. Changes were made to produce the version adopted by the RN but it was still basically the same weapon. The Hispano wasnt a mature weapon till after the Oerlikon was in full production.


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## fastmongrel (Mar 14, 2012)

Just read the link on the Oerlikon davebender posted and it says it took 30 seconds to change the barrel on an Oerlikon and an hour to change a Hispano barrel perhaps thats the clincher for a ships gun that could be firing for very long periods and be months between harbours.


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## davebender (Mar 14, 2012)

Aircraft cannon don't require a quick change barrel. That's probably why the historical Hs.404 cannon didn't have this feature. 

But what if Britain made a variant of the Hs.404 for ground use? Could this feature be added without too much trouble?


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## Shortround6 (Mar 14, 2012)

davebender said:


> Otto Carius thought the flakvierling an excellent weapon for employment against ground targets. I have no reason not to believe him.



Excellent against what type of targets and at what range?

A flakvierling weighs more than than a Pak 40 antitank gun or 7.5cm feild gun and only about 1000lbs less than a 10.5 cm howitzer. 

the eight man crew isn't exactly economical of manpower either. 

If you can get your enemy to attack with men in the open, un-armored or lightly armored vehicles and lacking in rapid response artillery of their own it can be a dandy weapon. 

Effective range about the same as an 81mm mortar. 

The US had some good success with the quad .50 anti-aircraft mount but nobody confused it with real artillery or anti-tank weapons.


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## Shortround6 (Mar 14, 2012)

davebender said:


> Aircraft cannon don't require a quick change barrel. That's probably why the historical Hs.404 cannon didn't have this feature.
> 
> But what if Britain made a variant of the Hs.404 for ground use? Could this feature be added without too much trouble?



Why?

The difference in ballistics is no more than the difference between a new barrel and a somewhat (but not ready for replacement) used one. 

The higher rate of fore for the Hispano isn't quite as important with multiple barrels per ship. Like dozens on large ships. 

Increasing maintenance requirements (man hours) probably isn't a good idea and on ships with salt air or mounted on tank chassis or on trucks the surface AA light AA gun spent a lot more time being worked on than it did even ready for action let alone actually shooting. 

British did come up with a new gun in the last year or two of the war, with a lot of Polish help. the Polsten gun.


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## fastmongrel (Mar 15, 2012)

davebender said:


> Aircraft cannon don't require a quick change barrel. That's probably why the historical Hs.404 cannon didn't have this feature.
> 
> But what if Britain made a variant of the Hs.404 for ground use? Could this feature be added without too much trouble?



Probably but your going to add weight. Also the Hispano would need to be navalised and have sights fitted, pretty soon its going to be approaching the weight of the Oerlikon. Higher rate of fire isnt necessarily a good thing for a free swinging AA cannon, controlled bursts is the thing just hosing a 60 round drum in the general direction isnt whats wanted. 

It could be made to replace the Oerlikon but after quite a deal of work what do you have a similar but slightly faster firing gun. Better get the Polsten going earlier it had the same performance but was considerably cheaper and easier to make, half the parts and half the cost I believe.


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## Shortround6 (Mar 15, 2012)

There were some Hispano's tried in a naval setting, either on a few warships or on armed merchant ships. This were it was found that they didn't do as well as the Oerlikon. They need much more maintenance to keep them in operating order. A Ship may go weeks between firing it's guns and just because the gun was good when you put a canvas cover on it two weeks ago doesn't mean it is good now. 

The Hs 404 has been used as both a naval AA gun and Ground AA gun post WW II with the Israelis being a prim example (replaced the four .50s on the M45 Maxon mount with two 20mm guns.) but that may say as much about which guns they had access to at the time as it does about how good they were for the job. US Navy used the MK 12 (updated Hs 404) in small patrol boats and such. Available surplus aircraft guns and parts vs older 20mm guns? 

The Hispano used a locked (or semi-locked) breech instead of pure blow-back which made it lighter and faster firing. It also meant more parts, more machining operations and more attention from the armorers. you seldom get something for nothing.


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## davebender (Mar 15, 2012)

> The Hispano-Suiza gun was never known for its reliability, regardless of the size in vhich it was built. Also it had to be kept clean and well lubricated, a difficult requirement in dusty or sandy environments.


Found the answer to my question in the Air Force Armament Laboratory evaluation. This probably also explains why the Hs.404 cannon had a relatively short post-war career.


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## Jabberwocky (Mar 15, 2012)

davebender said:


> Found the answer to my question in the Air Force Armament Laboratory evaluation. This probably also explains why the Hs.404 cannon had a relatively short post-war career.


 
HS 404 derivatives solidered on in active service in a variety of forms (Colt M12, M24, HS 804, AN/M3, 20 mm Mk 16) as aerial cannon and AA cannon until the late 1970s/early 80s. 

The reason the HS 404 itself fell out of use as a aerial cannon was that it was superseded by the march of technology: rotary, gast and gatling guns offered higher rates of fire and/or lower weight. The 20 x 110 round was also judged to be too light/too slow against the fighters/bombers being developed in the late 1950s.


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## davebender (Mar 15, 2012)

Why wasn't the MG151/20 superseded by that same march of technology? Even post-WWII France appears to prefer the German cannon over the Hs.404.


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## Jabberwocky (Mar 16, 2012)

davebender said:


> Why wasn't the MG151/20 superseded by that same march of technology? Even post-WWII France appears to prefer the German cannon over the Hs.404.



Ummm, perhaps because that's a factually inaccurate statement and the MG151/20 was passed by just as quickly and the French used the HS 404 more than the MG 151/20

The French used the HS 404 in a couple of domestic aircraft (Ouragan, early Mystere and various Arsenal and SNCAC prototypes) in the immediate post war period, but then went straight to the DEFA revolver cannon as their primary aircraft fixed armament up until the introduction of the GIAT 30mm in the late 1980s.

Use of the MG151/20 in a couple of French helicopters used by a handful of nations doesn't remotely compare to post war HS 404/HS 404 derivative use worldwide. 

The Hispano soldiered on in better than 2 dozen post-war fixed and rotary wing aerial platforms and a couple of naval platforms. Thousands, perhaps tens of thousands, of aircraft made in the post war era flew with HS 404 or derivatives as their armament; Venom, Vampire, Skyraider, Skyhawk, Corsair, Crusader, Cougar, Alouette, even the Tunnan!


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## Normanvac (Feb 23, 2018)

Hi I have been doing a little research into the Oerlikon 20mm canon and its various uses and it struck me that it was never, as far as I know, put into a tank turret. I would have thought that as a weapon in a recon tank perhaps the Vickers Light it would have been a great asset. Anyone got any info.


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