UK goes all-in on a HMG class gun in the mid-30'ies

[Shortround6]

In the Late Spring of 1941 the British could not get the .50 cal guns in the Tomahawks to function correctly and figured that the P-40s had a effective armament of four .303 guns. They were not counting on the .50s to fire when needed.

The .50 cal became known for it's reliability in later years (to a greater or lesser extent depending on location/installation) but assuming anybody's new gun would be trouble free in it's early life is not a good assumption.

 

[A.G. Williams]

Your website appears to be gone. Are you no longer hosting it, or did something else happen

Something else happened - I left my website to fend for itself for a couple of years while I was working on my latest book - Autocannon - and by the time I got back to it the website software was obsolete and I couldn't seem to get on with any of the replacements. So I've been struggling for months to get back in control, but my tired and ancient steam-powered analogue brain has great difficulty in dealing with digital problems. However, I do seem to be making progress with WordPress, so I'll battle on.

 

[z42]

In the Late Spring of 1941 the British could not get the .50 cal guns in the Tomahawks to function correctly and figured that the P-40s had a effective armament of four .303 guns. They were not counting on the .50s to fire when needed.

The .50 cal became known for it's reliability in later years (to a greater or lesser extent depending on location/installation) but assuming anybody's new gun would be trouble free in it's early life is not a good assumption.

Yes. To the extent this thread is about "what could the RAF have done to have more punch than the .303 at the outset of the war", if making the choice 1935-ish, it seems the pertinent choice isn't between HMG and autocannon, but rather between something that actually exists and something that is still early in the development cycle. So in this sense both the Hispano and the M2 (or variants thereof like the FN one discussed in this thread) were poor choices. Perhaps Anthonys suggestion above about the Oerlikon FFL would have been the optimal and realistic choice, considering it was available and a somewhat mature design by the mid 30'ies. Muzzle velocity and RoF somewhat worse than Hispano, true, but it seems RoF was improved during the war, so it would probably have been good enough as the main fighter armament for the duration of the war.

 

[A.G. Williams]

Incidentally, a comment on the 13.2 mm Hotchkiss case length: this was originally 99 mm but for the Model 1935 it was reduced to 96 mm. The reason for this was that the original loading proved to have unacceptable barrel wear. A competition was held to find a solution and the winner was a new bullet - but this needed crimping very firmly into the case which in conjunction with other dimensional requirements meant that the overall length of the cartridge was too great - so the case was shortened.

Also incidentally, Hotchkiss cases can be found shortened to 93 mm; that was to take German HE bullets to make ammo for use in captured guns.

 

[tomo pauk]

In the Late Spring of 1941 the British could not get the .50 cal guns in the Tomahawks to function correctly and figured that the P-40s had a effective armament of four .303 guns. They were not counting on the .50s to fire when needed.

The .50 cal became known for it's reliability in later years (to a greater or lesser extent depending on location/installation) but assuming anybody's new gun would be trouble free in it's early life is not a good assumption.

Id British decide to go with HMG, they will need to start with that business in early 1930s.

 

[A.G. Williams]

Perhaps Anthonys suggestion above about the Oerlikon FFL would have been the optimal and realistic choice, considering it was available and a somewhat mature design by the mid 30'ies. Muzzle velocity and RoF somewhat worse than Hispano, true, but it seems RoF was improved during the war, so it would probably have been good enough as the main fighter armament for the duration of the war.

Yes, I think so. But I would also like to have the next generation of aircraft guns under development, as the whole process takes so long.

One of my favourite postwar aircraft guns is the Soviet twin-barrel GSh-23, a very compact gun with a phenomenally high rate of fire (3,000+ rpm). That design was presumably inspired by the German Gast gun of WW1. Now it just happens that an example of the Gast was sitting in the Enfield Pattern Room from WW1+ (it is still there, in the NFC). Design a version in 25 mm calibre - perhaps using the 25.4 mm ammo from the Vickers naval gun, maybe shortened a bit - and that might have proved a better solution than the Aden, and available much sooner.

 

[tomo pauk]

One of my favourite postwar aircraft guns is the Soviet twin-barrel GSh-23, a very compact gun with a phenomenally high rate of fire (3,000+ rpm). That design was presumably inspired by the German Gast gun of WW1. Now it just happens that an example of the Gast was sitting in the Enfield Pattern Room from WW1+ (it is still there, in the NFC). Design a version in 25 mm calibre - perhaps using the 25.4 mm ammo from the Vickers naval gun, maybe shortened a bit - and that might have proved a better solution than the Aden, and available much sooner.

Madsen's 23mm cartridge was around in the mid-1930s if anyone was interested. As close equivalent to the Soviet 23x115mm as it gets.

 

[A.G. Williams]

Madsen's 23mm cartridge was around in the mid-1930s if anyone was interested. As close equivalent to the Soviet 23x115mm as it gets.

Yes, that's true, it's another option. The Madsen cannon ammo is a bit odd though, with a massively thick rim because the gun design leaves the rear of the case unsupported at one stage, so the case has to resist huge pressure. The gun itself is limited to around 400 rpm, maybe less, and has a massive receiver.

The 23mm Madsen was touted around various nations (inc the US, who was interested) but only a handful got into service.

 

[tomo pauk]

Yes, that's true, it's another option. The Madsen cannon ammo is a bit odd though, with a massively thick rim because the gun design leaves the rear of the case unsupported at one stage, so the case has to resist huge pressure. The gun itself is limited to around 400 rpm, maybe less, and has a massive receiver.

That would be 400 rd/min for a 175 gram shell - nice, very nice.
Luckily, there was no "MG 151/23".

 

[pbehn]

Yes, and the "shotgun" approach with lots of .303's was used as an argument why small caliber guns was better. The rather huge hole in that argument, of course, is that, statistically, "a hit" with .303's is very unlikely bring down a plane. While ultimately the autocannon side of the argument won, at least initially that side wasn't helped by the reliability and other issues with the initial Hispano installation.

In 1939/40 the 303 was undoubtedly better than either the 50 cal or the 20mm canon, because they worked reliably, By 1941 Spitfires Hurricanes Beaufighters Whirlwinds and Typhoons were all being fitted with a sorted 20mm cannon. At the end of 1941 into 1942 when the Mustang MkI P-51A first came into service it used a mix of 50cal and 30 cal AND the USA fitted long barrel 20mm cannon to those they took on charge after war was declared. Here a picture from wiki from October 1942. The Battle of Britain was won when Goering ran out of bombers. 8 x 303 may not have been the theoretical best at the time for bringing down a bomber, but the RAF shot down a lot, and a huge number landed in France and the low countries never to take off again. Talk of what one round can do is immaterial when the machine guns were in a battery of 8. Hitting a bomber with just one round from a Hurricane would require extraordinary skill

 

[z42]

In 1939/40 the 303 was undoubtedly better than either the 50 cal or the 20mm canon, because they worked reliably,

Well, I agree with that. My point with this thread in this "what-if" forum was to speculate on what the RAF could have done to have better punch early in the war.

The Battle of Britain was won when Goering ran out of bombers. 8 x 303 may not have been the theoretical best at the time for bringing down a bomber, but the RAF shot down a lot, and a huge number landed in France and the low countries never to take off again.

Again, I agree. I'm not disputing that the UK won the BoB. So if the RAF would have better armed fighters it wouldn't change the outcome, but maybe the British victory would have happened sooner, at less cost to the UK.

Talk of what one round can do is immaterial when the machine guns were in a battery of 8. Hitting a bomber with just one round from a Hurricane would require extraordinary skill

The shotgun argument was that a dense pattern was better because it would give a higher probability of a hit than with a slower firing battery of heavier guns. But in contrast to shooting birds with an actual shotgun where a single hit in the body tends to be enough to bring the bird down, shooting down even a single-engined fighter required, on average, a quite substantial number of .303 hits (~100??). So a solid well aimed burst was required in any case, and thus the "pattern density" argument is invalid as that same well aimed burst with a heavier gun battery would also guarantee a sufficient number of hits to bring the plane down even if the pattern density is lower.

 

[z42]

Yes, I think so. But I would also like to have the next generation of aircraft guns under development, as the whole process takes so long.

One of my favourite postwar aircraft guns is the Soviet twin-barrel GSh-23, a very compact gun with a phenomenally high rate of fire (3,000+ rpm). That design was presumably inspired by the German Gast gun of WW1. Now it just happens that an example of the Gast was sitting in the Enfield Pattern Room from WW1+ (it is still there, in the NFC). Design a version in 25 mm calibre - perhaps using the 25.4 mm ammo from the Vickers naval gun, maybe shortened a bit - and that might have proved a better solution than the Aden, and available much sooner.

Russian aircraft guns seem underappreciated, perhaps due to the typical WWII aviation interest focusing on the Western and Pacific fronts. For a slightly more modern take, the Gsh-30-1 seems like a pretty formidable package. A 46kg gun spitting out 30mm shells at 900m/s & 1800 rpm (apparently typically limited to 1500 rpm to reduce barrel wear). And it's a plain short-recoil operated gun, nothing that would be "exotic" from a WWII perspective like Gatling/revolver/Gast. Wonder if something like that would be doable in the WWII timeframe, or does it make use of advances in metallurgy etc. that weren't available then?

Something in the 25mm range firing at, say, 850-900 m/s, and up to 1200 rpm with a normal gas or short recoil operation doesn't sound totally unrealistic as a late WWII / early Cold War aircraft gun. Though I read somewhere (might even have been your writings..) that UK & France chose 30mm for the ADEN/DEFA cannons as they were expecting to be up against heavy Soviet bombers, and thus they evidently sacrificed a bit of muzzle velocity in order to get a beefier shell in a decent sized gun. Early jet age analog to the Mk 108, in a way.

 

[Shortround6]

this thread in this "what-if" forum was to speculate on what the RAF could have done to have better punch early in the war

We often focus on the guns (or going backwards, the aircraft) when what actually does the damage is the Bullets/projectiles.
The so called De Wilde bullet was much improved incendiary bullet over what used from WW I to about 1940 by just about everybody. Tracers aren't really much good, They can start fires which is rather different than WILL start fires. They are using up their incendiary material as they travel which means they are increasingly ineffective as the range increases. Likewise it was rather easy to armor against "ball" ammo but harder if you are using AP (hardened steel cores). The AP ammo also tends to penetrate a bit better into aircraft structure than the "ball" ammo. as stated earlier during beginning of the BoB 3 guns were loaded with ball, 1 had De Wilde (Dixon) incendiary, two had the old Mk IV incendiary/tracer, and two had AP.

By 1942 (?) Spitfires were using two .303s firing AP and two with the De Wilde/Dixon ammunition. The De Wilde/Dixon ammo was about twice as effective as the Mk IV incendiary/tracer at setting things on fire.

Actually teaching air to air gunnery before pilots were posted to operational squadrons might have helped, just a little bit

So if the RAF would have better armed fighters it wouldn't change the outcome, but maybe the British victory would have happened sooner, at less cost to the UK.

You are probably correct.

Wonder if something like that would be doable in the WWII timeframe, or does it make use of advances in metallurgy etc. that weren't available then?

Perhaps. It also requires a different standard of gun construction.
The US .50 cal and the Hispano were supposed to last around 10,000rounds and be able to be rebuilt (sometimes?) while the Soviet guns were junked a lot closer to 2,500 rounds.
That is not the life of the gun barrel, it is the life of the receiver. You could burn up barrels much quicker.

US standards for the M2 aircraft gun were not to exceed 150 rounds continuously from a cold barrel without hitting cook off temperature and the restrictions after that were pretty absurd for air to air combat. You don't get 5 minute cool down periods in combat . And 5 minutes does not get you back to the cold barrel state. More like you are "allowed" to fire a 25 round burst and then wait several more minutes.

BTW the Belgian 13.2mm gun was supposed to use a barrel a couple of pounds lighter than the M2 if the spec sheet is right. This helps speed things up just a bit (along with changes to bolt, spring and buffer) but means you hit cook off temperature sooner.

 

[ColFord]

At the end of 1941 into 1942 when the Mustang MkI P-51A first came into service it used a mix of 50cal and 30 cal AND the USA fitted long barrel 20mm cannon to those they took on charge after war was declared.

The Mustang Mk.I - NA-73 and NA-83 in NAA parlance with no P-51 designation because they were a direct contract purchase between NAA and the UK, had the initial mixed armament of 0.5in and 0.300in. When the design specifications/requirements were originally given to NAA, they asked for it to have a 4 x 20mm Hispano armament, but availabilty and supply of the 20mm was not guaranteed, so they went with the mixed HMG & MG armament. However, NAA in designing the wing armament bays for the Mustang I, took account of the requirement for the future 4 x 20mm armament in both terms of size and strength of the bays. The third Mustang variant to be produced was the NA-91, which was the Mustang Mk.IA in RAF service, 150 of which were ordered for the RAF under Lend Lease and the first to be given the P-51 designation - no suffix. It was also the first to receive the RAF's requested 4 x 20mm cannon armament, and as supplied were delivered with Oldsmobile licence manufactured 20mm Hispano cannon. So there was no initial changes between the RAF and USAAF P-51/Mustang Mk.IA as delivered in terms of armament. The USAAF when they took over part of the RAF Lend Lease order got exactly same as the RAF. The fourth Mustang variant to be manufactured, which was to an order for the USAAF, was for the NA-97, which was the A-36A, which had the armament dictated by the USAAF of 6 x 0.5in HMGs. The fifth Mustang variant to be manufactured was the NA-99, the P-51A, (RAF got 50 as the Mustang Mk.II) which had the nose guns from the previous A-36A deleted and just retained the four x 0.5in HMGs in the wings.

 

[RCAFson]

The RN compared the Vickers .5in and the Browning .5in during comparative trials for a quad .5in naval AA mounting. The Vickers gun was chosen because it was more reliable:
"

1. Greater reliability
2. Wear and failure of parts – if any – are to minor parts that can be readily replaced.
3. Care and maintenance is easier to the inexpert, on account of its less complicated recoil and buffer mechanisms.
4. The mechanism and functioning of the gun requires less special or expert knowledge to obtain a good, reliable performance, and is more readily understood by the average seaman, who already receives training in the similar mechanism of the .303-inch gun.
5. Readily converted to right or left gun.
6. From a general technical point of view, it is the opinion that the fundamental principle of the mechanism and the action of the Vickers gun is superior to that of the Browning, and is more certain in its action generally.

The .5-inch Vickers gun is therefore recommended for the Naval service in preference to the Browning gun." (Small Arms Review V15N4 (Jan 2012), Volume 15)

 

[Clayton Magnet]

Russian aircraft guns seem underappreciated, perhaps due to the typical WWII aviation interest focusing on the Western and Pacific fronts. For a slightly more modern take, the Gsh-30-1 seems like a pretty formidable package.

Agreed. The Gsh-30-1 is an impressive achievement, in its simplicity and compact size. For me, the WWII equivalent to the Gsh-30-1 is the Berezin B-20. Simple, lightweight, excellent rate of fire and reliability, just a short service life.
Perhaps in this "what-if" scenario, the RAF should have taken a look at the Berezin UB, but it wouldn't have been available in the 30's timeline

 

[pbehn]

The shotgun argument was that a dense pattern was better because it would give a higher probability of a hit than with a slower firing battery of heavier guns. But in contrast to shooting birds with an actual shotgun where a single hit in the body tends to be enough to bring the bird down, shooting down even a single-engined fighter required, on average, a quite substantial number of .303 hits (~100??). So a solid well aimed burst was required in any case, and thus the "pattern density" argument is invalid as that same well aimed burst with a heavier gun battery would also guarantee a sufficient number of hits to bring the plane down even if the pattern density is lower.

I didnt make the shotgun argument. The calculations of rate of fire, weight of round etc have een shown by others. In the late 1930s into 1940 there wasnt a reliable 50cal to get off the shelf. Weight was of great importance, the total weight of all guns and ammunition. A 1939 Mk I Spitfire had 1030 BHP and a fixed pitch prop meaning it only had 660BHP at take off (at max revs the prop was "stalled"). By 1941 the Merlin 45 fitted in the Spitfire Mk V had 1515 BHP and a CV prop.

 

[Shortround6]

A 1939 Mk I Spitfire had 1030 BHP and a fixed pitch prop meaning it only had 660BHP at take off

Goes go for the Hurricane also.

And even with two pitch propeller (or constant speed) the 1939 Merlin III was only good for 880hp for take-off, assuming the pitch was set for that and that might be well be assumption for the two pitch prop. And the two pitch versions didn't climb that well. The Two pitch got them off the runway but at 2850rpm max speed was about 140mph. Switching to high pitch (some aircraft could be adjusted) dropped the RPM to 2080rpm at 2,000ft and could slowly be increase as altitude was gained.

 

[pbehn]

Goes go for the Hurricane also.

And even with two pitch propeller (or constant speed) the 1939 Merlin III was only good for 880hp for take-off, assuming the pitch was set for that and that might be well be assumption for the two pitch prop. And the two pitch versions didn't climb that well. The Two pitch got them off the runway but at 2850rpm max speed was about 140mph. Switching to high pitch (some aircraft could be adjusted) dropped the RPM to 2080rpm at 2,000ft and could slowly be increase as altitude was gained.

Although they all got CS props for the battle of Britain the issue of time to climb still remained. In October 1940 the LW were sending Bf109s across the Channel at 30,000 ft to bomb London, at high altitude with limited power weight is a big issue.

 

[Shortround6]

Although they all got CS props for the battle of Britain the issue of time to climb still remained. In October 1940 the LW were sending Bf109s across the Channel at 30,000 ft to bomb London, at high altitude with limited power weight is a big issue.

There are some documents that say climb was raised to 2850rpm but other tests in the summer of 1940 give a 2600rpm limit for climb when not in combat.
Which is a bit late for changing the armament.
The Spitfire II got the Merlin XII and there is no doubt that was rated at 2850rpm for climbing and in fact was allowed 9lb of boost.