Big Guns aloft in WW2

[SplitRz]

In a previous thread, a contributor made some very interesting comments about the relative weakness of the Vicker S and RR 40mm guns used in the Hawker Hurricane iiD

It tied in (and contrasted) with a rather excellent video I saw on youtube a while back, which featured first hand accounts and reminiscences of Mosquito Tsetse pilots. Specifically, they were all in praise of the Molins gun accuracy and effectiveness.

It got me pondering the relative benefits and disadvantages of large bore weaponry (20mm and above) in aircraft - and how they served in contrast and compared to rocket projectiles (which had largely replaced anything above 30mm by the end of the war.)

Lots of things to potential think about:

- The numbers and types of aircraft and types sporting autocannon at the /early stages of the war / late 30s designs; P 39, P38, many 37mm, the various attempts to shoe-horn the COW gun into UK designs for bomber destroyers etc...
- As the war progressed, the incorporation of high velocity anti tank guns into aircraft such as the Stuka, HS 129
- The effectiveness of smaller by efficient Russian cannon like the ShVAK and Volkov-Yartsev
- Mounting of 75mm howitzer on the B25G

Anyway, have a watch of the vid about the Tsetse.

Your thoughts, observations, links and facts on the subject gratefully received

 

[tomo pauk]

...
It got me pondering the relative benefits and disadvantages of large bore weaponry (20mm and above) in aircraft - and how they served in contrast and compared to rocket projectiles (which had largely replaced anything above 30mm by the end of the war.)
...

A lot depends on what the targets are going to be. If the likely enemy is fielding (or is expected to field) a considerable fleet of heavy bombers (be those 2- or 4-engined types), cannons beyond 20 mm make sense. This was the case for Germany and Japan later in the war, and a lot of countries felt the same before that. One 30mm might weight 2-3 times as much as a 20mm gun, the 30mm set-up offering the same target effect as 3-4 20mm cannons. (Germans judged that a B-17 will go down after it received twenty 20 mm shells, vs. just five 30 mm shells, vs. a single 5cm shell; all shells being of 'Mine' type)
Or, go with 2-3-4 30mm cannons, that can offer the firepower like 6-12 20mm cannons. Obviously, installing more than 6 cannons on a fighter - even if it has 2 engines - is quite a challenge on it's own. Some fighters were more less limited to just a single cannon unless the other cannons are carried under the wings, here it pays well if the gun is as big and thus as powerful as possible. We can recall that Soviets were fond with 37mm cannons (either their or American), where just a 1 hit was sometimes enough to down a Ju-88.
Another targets 'worthy' of having a big cannon are the tanks, especially if the enemy has a lot of them. Again, Germany is in the focus here, and Soviets just after them. This is why we read about the Ju 87, Il-2 or Hs 129 lugging the biggest cannon that was practically possible. Not forgetting the progenitor, of course - Hurricane IVD.

Main limiting factor is the capability of airframe to 'receive' the required guns; especially the 1-engined A/C were tricky to up-gun. If you have an engine conductive for a 'motor cannon' installation, it might offer the easiest installation for a big gun (but it is not a guarantee). If not, big cannons need to go under the wings; some A/C being better in this regard than the others.
(it is much as the soldier being the limiting factor on what kind of rifle/cartridge is best for small arms)

Sorry for lecturing a lot

 

[fastmongrel]

relative weakness of the Vicker S and RR 40mm guns used in the Hawker Hurricane iiD

An Italian, German or Japanese soldier looking for cover while Hurricane can openers attacked would probably not consider a 2 1/2lb HE shell or 3lb AP shot weak

 

[glennasher]

To me, there's a point of diminishing returns, adding too much gun detracts from an aircraft's usefulness. While the fellows in the video didn't dismiss the 6 pounder in the Mosquito, it seems to me that it might be too much of a good thing, not enough ammo to do a lot of good, and the rate of fire leaves something to be desired (and at that, they never brought a Tsetse back empty of 57mm ammo).
I suspect the issue was worse with the 75mm gun in a B-25, unless you were doing anti-barge work in the Solomons or New Guinea, maybe. Did they even use those in the Bismark Sea fight? I have a lot more questions than I do answers, just like everyone else..

 

[A.G. Williams]

In a previous thread, a contributor made some very interesting comments about the relative weakness of the Vicker S and RR 40mm guns used in the Hawker Hurricane iiD

It tied in (and contrasted) with a rather excellent video I saw on youtube a while back, which featured first hand accounts and reminiscences of Mosquito Tsetse pilots. Specifically, they were all in praise of the Molins gun accuracy and effectiveness.

It got me pondering the relative benefits and disadvantages of large bore weaponry (20mm and above) in aircraft - and how they served in contrast and compared to rocket projectiles (which had largely replaced anything above 30mm by the end of the war.)

The big advantage of guns over rockets was accuracy. On test, the Hurricane IID with its twin 40mm S Guns scored 25% hits against tank-sized ground targets, while the Tsetse scored about 33%. RAF fighter-bombers with underwing rockets scored around 5% hits in practice, but the trajectory was strange, requiring lots of mental calculation, and in battle it was discovered that only 0.5% hits were scored. This improved somewhat when special sights were introduced, but guns remained more accurate by an order of magnitude.

The disadvantage of guns was their lack of flexibility. Once a fighter-bomber has fired his rockets, he can revert to being a fighter (Hurricane IV excluded), but the guns of the Hurricane IID and Tsetse were pretty well useless against enemy fighters. The RAF was much in favour of being able to switch their fighters from ground attack to aerial combat as the circumstances dictated. I suspect that the infantry on the ground would rather keep the ground-attack planes around...

 

[pbehn]

I think the problem with the Tsetse was how long you had to fly straight and level and how few rounds you got off in that time. Firing at 1 round per second you cover 140meters at 300MPH.

 

[SplitRz]

To me, there's a point of diminishing returns,

Agreed. Though its interesting to ponder where that point lies. In terms of power to weight - and relative power of weapon, you might at first think that the Stuka with twin 37mm was a classic example of a low powered aircraft lugging too much . And yet it was an extremely effective weapon. Arguably far more so than the Hurricane iiD and later IV with 'universal wing'. (thats born out by simply looking at the comparative shell velocities: an asthmatic 1,870 ft for the Vickers S, versus the 3,800–2,600 ft/s for the 3.7mm bordkanone) ....BUT.... the 40mm was obviously still good enough to tackle Ha-Gos and Chi-Ha in the far East. And with the accuracy on tap, probably a far more efficient and cost effective option...

Role and target is obviously key - whether its air land or sea targets. And another chunk of the appropriateness seems to depend on aerial opposition and whether one side or the other has air supremacy, I'd guess.

A good example of diminishing returns might well be the 75mm in the B25G. *Really* slow firing - and presumably not worth the effort and performance penalty, given it seems many squadrons in the field replaced it with a bank of .50 cals...

 

[SplitRz]

I think the problem with the Tsetse was how long you had to fly straight and level and how few rounds you got off in that time. Firing at 1 round per second you cover 140meters at 300MPH.

Yes - but its an interesting quandary, isn't it? Fire off your salvo of RPs, knowing you have a relatively statistically low chance of hitting your target - Or utilise a weapon which has a much higher chance of hitting 'per projective fired', and which allows you to either make another pass, or move onto another target. Destructive firepower versus accuracy - rather like the diminishing returns of size of gun, there's a theoretical middle ground, I suppose. Those old boys talking about the Tsetse certainly seemed to think that they had a good weapons system - even if it wasn't widely adopted by that stage of the war.

 

[tomo pauk]

Agreed. Though its interesting to ponder where that point lies. In terms of power to weight - and relative power of weapon, you might at first think that the Stuka with twin 37mm was a classic example of a low powered aircraft lugging too much . And yet it was an extremely effective weapon. Arguably far more so than the Hurricane iiD and later IV with 'universal wing'. (thats born out by simply looking at the comparative shell velocities: an asthmatic 1,870 ft for the Vickers S, versus the 3,800–2,600 ft/s for the 3.7mm bordkanone) ....BUT.... the 40mm was obviously still good enough to tackle Ha-Gos and Chi-Ha in the far East. And with the accuracy on tap, probably a far more efficient and cost effective option...

Shell velocities don't paint the complete picture. The Vickers S fired a 1.36 kg AP projectile, the 37mm cannon used on Ju 87G fired a 0.41 kg projectile. At the end of the day, both aircraft were good in making holes in medium tanks of the enemy, while also being close to useless in doing the same against the enemy's heavy tanks. Germans went for 7.5cm AT gun suspended under the Hs 129 for a reason.
Vickers S was also tested with an 1 lb (0.454 kg) projectile using the Littlejohn adpter), good for 3250 ms, improving practical AP performance by ~50%. Never used, though. link

Role and target is obviously key - whether its air land or sea targets. And another chunk of the appropriateness seems to depend on aerial opposition and whether one side or the other has air supremacy, I'd guess.

A good example of diminishing returns might well be the 75mm in the B25G. *Really* slow firing - and presumably not worth the effort and performance penalty, given it seems many squadrons in the field replaced it with a bank of .50 cals...

Good points.
75 mm gun aboard the B-25 was not worth it in Pacific - ships required bombs to be killed, while batteries or HMGs catered for 'lesser' surface targets, again helped out with bombs in different 'flavors'. Half, let alone or a full dozen of HMGs will trash people aboard the ships, including the AA gunners.

 

[SplitRz]

The disadvantage of guns was their lack of flexibility. Once a fighter-bomber has fired his rockets, he can revert to being a fighter (Hurricane IV excluded), but the guns of the Hurricane IID and Tsetse were pretty well useless against enemy fighters. The RAF was much in favour of being able to switch their fighters from ground attack to aerial combat as the circumstances dictated. I suspect that the infantry on the ground would rather keep the ground-attack planes around...

I think yes, but with some extra considerations. The Hurricane was certainly lumbered with the 40mm and suffered a big performance penalty (as did the Stuka) - but I cant see any specifics on whether the Tsetse suffered much. I suspect the weight of the four 20mm and ammo removed in lieu, plus the Mosquitos extra power and weight carrying capability probably meant that any performance penalty was relatively minimal. (Though I can't confirm or disprove that, as yet I can't find any specific performance stats for it!).

Until right at the end of the war when the RAF adopted 'zero zero' launchers, any aircraft using RPs was lugging whacking great draggy launch rails under their wings suffered a permanent performance penalty. So whilst the idea that once they'd fired off their rockets, they could revert to fighters bore weight later on, from 42 through to pretty much the end of the war it still came at a significant price. From what I can remember, Typhoon squadrons also largely stuck to their roles, be they 'bombphoons' or rocket armed and didn't tend to swap around their specialisms - which required rather specific techniques. I guess the airframe remained technically versatile, though in operational practice, I think it remained largely theoretical. Typhoons and other aircraft still lumbered with their bomb racks or RP-3s would still be at a significant performance and combat disadvantage compared to their opponents. But by the stage of the war that it mattered most, air superiority had already been achieved.

I suspect much of the preference for RP-3s was economic and the simplicity of converting aircraft, rather than using a special design

 

[pbehn]

Yes - but its an interesting quandary, isn't it? Fire off your salvo of RPs, knowing you have a relatively statistically low chance of hitting your target - Or utilise a weapon which has a much higher chance of hitting 'per projective fired', and which allows you to either make another pass, or move onto another target. Destructive firepower versus accuracy - rather like the diminishing returns of size of gun, there's a theoretical middle ground, I suppose. Those old boys talking about the Tsetse certainly seemed to think that they had a good weapons system - even if it wasn't widely adopted by that stage of the war.

It all depends on the target. You don't want to attack a flak ship with just Tsetse Mosquitos. Rockets were a stand off weapon which were much safer to use if not so accurate. A Mosquito with 4 x 20mm cannon fires 40 rounds to the Tsetse's 1 round. At Falaise, rocket and cannon armed Typhoons didn't knock out many tanks, they did knock out a lot of everything else, even veterans were shocked at the devastation.

 

[SplitRz]

It all depends on the target. You don't want to attack a flak ship with just Tsetse Mosquitos. Rockets were a stand off weapon which were much safer to use if not so accurate. A Mosquito with 4 x 20mm cannon fires 40 rounds to the Tsetse's 1 round. At Falaise, rocket and cannon armed Typhoons didn't knock out many tanks, they did knock out a lot of everything else, even veterans were shocked at the devastation.

Yes. 'Target specificity' (have I just invented that?! lol) must have an important bearing.

Spaffing a salvo of RP-3s at a mass of men and machines crammed on a road is just the right job for a rocket; its poor accuracy is largely immaterial - 8 60lbs warheads are likely to hit somewhere along a big target, and against soft skinned targets, are bound to be devastating. Paradoxically, Falaise also showed how very few tanks were actually knocked out by RP-3s. But it also proved that it might be immaterial: What did for the the tanks was that all the fuel bowsers, recovery vehicles, trucks carrying spare track pins wheels and ammo, lubricants, replacement crews, bridging equipment etc etc had all been pulverised. And I'd imagine there's also a massive morale factor. If you have the choice of being dived at by an aircraft shooting at the area in which you're trying to find cover, seeing some tracer and hearing gunfire is probably going to be preferable to seeing the firework show of 8 rockets streaking down at you - followed by the crump of 8 x 60lb warheads going off. And multiply that by a squadron, then by several of those and you have something which is going to be truly terrifying. Even hardened troops and tank crew might crack under that - and it seems borne out by history,

And also agree that making 57mm holes in any ship over a couple of thousand tonnes isn't going to do much very quickly. The Molins was obviously most at home punching through the pressure hulls of notoriously slim and difficult targets like U-Boats.

Interestingly, I've read that the 60lbs RP warheads weren't used on U-Boats - they used a 25lb non explosive armour piercing warhead instead. Though this must have been far less accurate than the Molins - and also added extra complication regarding any finned rocket's tendency to 'weathervane' into wind.

 

[SplitRz]

Rockets were a stand off weapon which were much safer to use if not so accurate.

Were RP3s fired from a longer range than a 40mm or 57mm round?

They're a low velocity weapon and inherently less accurate than a projectile fired from a rifled barrel. Trajectory drop (as well as 'weather-vaning') would be a huge problem at longer ranges. Surely any pilot would want to get as close as possible to have even a low chance of hitting the target?

I wonder if we can track down any info on the ranges at which pilots were trained to fire them?

Cameras can be very misleading, but this doesn't look any more stand off than gunfire to me!

 

[Greyman]

The use of RP with 25-lb heads vs. ships / subs involved a pretty unique attack.

They were actually used kinda like rocket torpedoes -- the standard attack* being a:

- firing range of 600 yards​

- 12 degree dive​

- salvo should hit 50 ft. short​

On hitting the water the rocket's trajectory flattened out and plowed into the vessel's hull underwater, hopefully with propellant still burning.

*variation on this depending on circumstances/target, as well as the date. IE: the prescribed parameters were different at different stages of the war.

 

[Glider]

Regarding the accuracy. My son once had a German girlfriend whose father was on the flak ships based in Norway. He told Peter that they really didn't like the 'big gun' mosquito's as it was almost personal. If they wanted to take out a gun position they felt they could, if it was the bridge it would be the bridge. Strangely they recognised that the rocket firing mosquitos were more dangerous, but they seemed less personal, as they were just firing at the ship.

 

[SplitRz]

Regarding the accuracy. My son once had a German girlfriend whose father was on the flak ships based in Norway. He told Peter that they really didn't like the 'big gun' mosquito's as it was almost personal. If they wanted to take out a gun position they felt they could, if it was the bridge it would be the bridge. Strangely they recognised that the rocket firing mosquitos were more dangerous, but they seemed less personal, as they were just firing at the ship.

Thats really fascinating - and again, testament to the accuracy of the Tsetse - but also the practical advantage against a flak ship of the rockets. Thank you so much - real anecdotes like this bring conversations to life and give them so much more meaning.

 

[SplitRz]

The use of RP with 25-lb heads vs. ships / subs involved a pretty unique attack.

They were actually used kinda like rocket torpedoes -- the standard attack* being a:

- firing range of 600 yards​

- 12 degree dive​

- salvo should hit 50 ft. short​

On hitting the water the rocket's trajectory flattened out and plowed into the vessel's hull underwater, hopefully with propellant still burning.

*variation on this depending on circumstances/target, as well as the date. IE: the prescribed parameters were different at different stages of the war.

Ask on this site, and ye shall receive, it seems! Thank you so much for this! Grayman = Wiseman

Is it probably fair to say then, if a U-Boat is roughly 40 x 8 x 4 meters, and a tank is approx 7 x 4 x 3, any pilot is going to want to get much closer to such a small target...?

 

[Glider]

The use of RP with 25-lb heads vs. ships / subs involved a pretty unique attack.

They were actually used kinda like rocket torpedoes -- the standard attack* being a:

- firing range of 600 yards​

- 12 degree dive​

- salvo should hit 50 ft. short​

On hitting the water the rocket's trajectory flattened out and plowed into the vessel's hull underwater, hopefully with propellant still burning.

*variation on this depending on circumstances/target, as well as the date. IE: the prescribed parameters were different at different stages of the war.

I think different units sometime developed their own tactics. I read the biography of a Beaufighter pilot, whose squadron used a shipwreck to develop their tactics. They ended up sighting the 20mm cannon to 800 yards. When attacking they fired the 20mm and when the shells matched the sight on the target they salvoed the rockets. Using this approach they were confident that a minimum of three rockets would hit the target.
The rockets that hit above the waterline stood a good chance of starting a fire caused by the propellent, those that his below the waterline started serious leaks. A win win situation, but I did wonder how much use the sights would be if they had to shoot at aircraft

 

[SplitRz]

I think different units sometime developed their own tactics. I read the biography of a Beaufighter pilot, whose squadron used a shipwreck to develop their tactics. They ended up sighting the 20mm cannon to 800 yards. When attacking they fired the 20mm and when the shells matched the sight on the target they salvoed the rockets. Using this approach they were confident that a minimum of three rockets would hit the target.
The rockets that hit above the waterline stood a good chance of starting a fire caused by the propellent, those that his below the waterline started serious leaks. A win win situation, but I did wonder how much use the sights would be if they had to shoot at aircraft

Probably not too much of an issue - the Hispano had a fairly high velocity: Conveniently for my crap maths, its actually at about 840–880 m/s (2,800–2,900 ft/s)... Drop for a 20mm round moving at that speed shouldn't have been that significant at 800m, I would have thought? Less than a second from muzzle to target... And the other advantage of course is that the Beaufighter's cannons were closely grouped in the belly, so again, less issue with convergence to contend with that wing guns would have introduced. But this isn't my area of expertise - as I have the honour of having AG Williams commenting on this thread his word on this would be the best to go on.

 

[pbehn]

Thats really fascinating - and again, testament to the accuracy of the Tsetse - but also the practical advantage against a flak ship of the rockets. Thank you so much - real anecdotes like this bring conversations to life and give them so much more meaning.

I read it differently. Whatever the Tsetse pilot actually had in his sights he was aiming at the ship, where it hit as an individual shell felt personal. If you watch footage of a ship being attacked with 4 x 20mm cannon they have hits from stem to stern. Sailors under attack by kamikaze planes felt they were the target, even though the attacking pilot may well have been dead when their ship was hit.