About WW2 fighter aircraft firing power

[Harri Pihl]

Originally Posted by Tony Williams

Better known as the Browning .50 M2...it depends on how you measure success. Certainly US fighters armed with the .50 shot down lots of planes, but there are other factors involved than the quality of the gun: such as the superiority of the aircraft, the superiority of pilot training, superiority in numbers (later) and so on. And of course the fact that few planes carried anything other than the .50 meant it was bound to shoot down a lot of planes. What that doesn't tell you is whether or not they would have been even more successful if armed with a good cannon: personally, I think they would.

I'm not arguing wether USAF swould have done better with something else than the M2. I merely replied to your point that the Germans and Russians went towards lower velocity, higher caliber weapons, my point being that the USAF stayed on higher velocity weapon, the M2, and even did consider another high velocity weapon, the 15mm MG 151, which was replaced by lower velocity weapon in Germany. In other words I'm saying that the air forces selected weapons with different standards and the USAF experience is just as relevant as German and Russian experience because the USAF results are undeniable (actually same can't be said about German results).

Infact I agree with you that the USAF might have done better by adopting a cannon like the Hispano or the MG 151. However, it's not the point discused here.

[Rob Philips]

Thanks, Tony. 3 and 4 point harmonisation added to the list too.

Assume an engagement range of 200 meters. Small caliber projectiles, Vo say 850 m/s, V200 say 650 m/s, Vaverage over that trajectory say 700 m/s, would take 200/700 = 0,29 second only to reach the target. Forgetting about a quantification of the violent evasive action capabilities of the target, and same for the attacker to follow that evasive action, and forgetting about a pattern fired so far forward that the pilot in the target had a reaction time in the >0,5 second area, then would your idea still hold? It would interest me to hear about this from those who have been up there. The point is, or could be, that small caliber rounds flying at such velocities cannot be seen. Neither by the attacker, nor by the pilot in the target aircraft. The flying noise would be such that they could not hear the projectiles in flight either. From my own experiments it follows that a small caliber projectile, meaning <10mm, can be seen, if you are focussed and if lighting conditions are good, only at speeds well below 200 m/s. Poor sample count in this experiment; I assume my eyes to be as sharp and as fast as the eyes of the average guy. This might be a bit different if there is a dense pattern flying around, I don't know. It seems that there is a clear benefit in this type of extremely fast four dimensional shooting, if you can see where the pattern is going. The fighter pilot is there to control the aircraft which is there to carry & aim the guns. It seems that a tracer path offers a more intuitive picture than any gun sight could do, in the days of unguided ammunitions.

Regards,

Rob

[Tony Williams]

Originally Posted by Harri Pihl

I'm not arguing wether USAF swould have done better with something else than the M2. I merely replied to your point that the Germans and Russians went towards lower velocity, higher caliber weapons, my point being that the USAF stayed on higher velocity weapon, the M2, and even did consider another high velocity weapon, the 15mm MG 151, which was replaced by lower velocity weapon in Germany. In other words I'm saying that the air forces selected weapons with different standards and the USAF experience is just as relevant as German and Russian experience because the USAF results are undeniable (actually same can't be said about German results).

Infact I agree with you that the USAF might have done better by adopting a cannon like the Hispano or the MG 151. However, it's not the point discused here.

To be precise, the M2 was a moderately high-velocity gun (the muzzle velocity was little more than the 20mm Hispano's) and they rejected an extremely high-velocity one (the T17 - the MG 151 copy - was chambered for the US 15.2x115 round, far more powerful than the MG 151's 15x96).

I suspect that there were two reasons why the US stayed with the .50: it was the only reliable aircraft gun they had, and it proved adequate as long as they fitted at least six of them. That is not exactly a ringing endorsement.

The following extract from a 1944 US evaluation may be of interest:

"As it is now, we have the 50-cal. gun which has reached its peak. The only improvements will be minor. The only good increase is to increase the number of guns. So it seems to be just about the right time to look for a better weapon. There are two possibilities here - the one we have and the one we might get shortly. The one we have is a 20-mm gun. I think very highly of it. In fact, it is one we have here, and it is one in hand. It won't do what the 60 will do, but we haven't got the 60, and we won't have it for a year. So, we are gradually working into all of our aircraft the 20-mm gun. To give you some idea of the 50 versus the 20 and dispel a lot of ideas that have bothered us, I would like to give you a comparison. When somebody goes from four 50's to two 20's, to the layman that means a decrease in fire power. Actually, quite the reverse is true. In the horsepower of the gun, one 20 is equal to three .50-calibers. In the actual rate of fire delivered at the target, one 20 equals three 50's; in kinetic energy at 500 yards, one 20 equals two and one half 50's.[N.B. This takes no account of the effect of the HE content of the 20mm shells]

That adds up to four 20's equaling twelve 50 calibers, judging by those standards. Of course you have other advantages of the 20. You have the much greater penetration of armor. The 20 will go through 3/4 inch of armor at 500 yards, while the .50 cal, will go through only .43. In addition to that you have one more great advantage - that is you can have longer and more frequent bursts without damage to the gun with the 20 than you can have from the .50 cal. That is important for the strafing airplane, because they are burning up their barrels and ruining their guns on one flight. Sometimes it is long before that one flight is over. They will come down with screaming barrels and get trigger happy, and then all the barrels are gone in one flight. It should not happen in a 20mm. Of course, you have disadvantages. You have a heavier installation, one-half as much ammunition for the same weight. Our standard ammunition in the Navy is 400 rounds in one gun. The Fleet has set up 30 seconds of fire as a minimum requirement for the .50 cal gun. We can't do that with the 20, so we give them 200 rounds. The 20 is lethal enough to get far more results out of that 200 rounds than the .50 ever will out of 400 rounds."

From: "USN Report of Joint Fighter Conference NAS Patuxent River". (October 1944)

[PeterVerney]

Fascinating stuff. Actually our pilots were taught deflection shooting on the Mosquito which had a fixed ring gun sight!.
The radius could be varied by setting the span of the target aircraft and so the range would be correct when the targets span filled the ring. With me so far; then pilots were taught to "lead off" by say "half a rad", or "one and a half rads", according to their judgement of angle off and closing speed.
If you have shot birds or game with a shotgun you will know what I mean. In fact we had a supply of shotguns, clay pigeons and ammo so that the pilots could practice. In addition we did many sorties of "cine", where aircraft flew in pairs and took turns to be fighter and target. High quarter attacks were the norm and cine taken when the pilot judged he was right. Then the films were assesed, frame by frame to judge how good the pilot was and he was criticised as required. I used to help our gunnery officer by doing some of this tedious work, in retrurn for a go on the clay pigeon shoots.
When we got the Meteor, with a gyro gunsight, of course things were much easier to assess, but as in all instances accurate flying was essential.
I must visit the NA again, I had no idea of all those references that's a goldmine. What I put down here is dredged from some recess of my antique brain.

[Rob Philips]

Thanks, Peter. Your brain is probably well filled rather than antique. Furthermore, that term also means "value increases with age".

The statement that clay pigeon shooting was one form of preparation for aerial combat, is very clarifying.

Regards,

Rob

[Harri Pihl]

Originally Posted by Tony Williams

To be precise, the M2 was a moderately high-velocity gun (the muzzle velocity was little more than the 20mm Hispano's) and they rejected an extremely high-velocity one (the T17 - the MG 151 copy - was chambered for the US 15.2x115 round, far more powerful than the MG 151's 15x96).

The point is that USAF did not go towards lower velocity weapons like the Germans; possible replacements of the M2 had about same or higher muzzle velocity.

Originally Posted by Tony Williams

I suspect that there were two reasons why the US stayed with the .50: it was the only reliable aircraft gun they had, and it proved adequate as long as they fitted at least six of them. That is not exactly a ringing endorsement.

My impression is that good combat results were the main reason why USAF (and NAVY) continued with the M2 despite obvious benefits of the possible replacements. Note that at spring 1944 the P-51B, with only four M2s, proved to be extremely succesfull despite the problems with gun feed etc. some pilots prefered it over the P-51D.

Originally Posted by Tony Williams

The following extract from a 1944 US evaluation may be of interest:

"As it is now, we have the 50-cal. gun which has reached its peak. The only improvements will be minor. The only good increase is to increase the number of guns. So it seems to be just about the right time to look for a better weapon. There are two possibilities here - the one we have and the one we might get shortly. The one we have is a 20-mm gun. I think very highly of it. In fact, it is one we have here, and it is one in hand. It won't do what the 60 will do, but we haven't got the 60, and we won't have it for a year. So, we are gradually working into all of our aircraft the 20-mm gun. To give you some idea of the 50 versus the 20 and dispel a lot of ideas that have bothered us, I would like to give you a comparison. When somebody goes from four 50's to two 20's, to the layman that means a decrease in fire power. Actually, quite the reverse is true. In the horsepower of the gun, one 20 is equal to three .50-calibers. In the actual rate of fire delivered at the target, one 20 equals three 50's; in kinetic energy at 500 yards, one 20 equals two and one half 50's.[N.B. This takes no account of the effect of the HE content of the 20mm shells]

That adds up to four 20's equaling twelve 50 calibers, judging by those standards. Of course you have other advantages of the 20. You have the much greater penetration of armor. The 20 will go through 3/4 inch of armor at 500 yards, while the .50 cal, will go through only .43. In addition to that you have one more great advantage - that is you can have longer and more frequent bursts without damage to the gun with the 20 than you can have from the .50 cal. That is important for the strafing airplane, because they are burning up their barrels and ruining their guns on one flight. Sometimes it is long before that one flight is over. They will come down with screaming barrels and get trigger happy, and then all the barrels are gone in one flight. It should not happen in a 20mm. Of course, you have disadvantages. You have a heavier installation, one-half as much ammunition for the same weight. Our standard ammunition in the Navy is 400 rounds in one gun. The Fleet has set up 30 seconds of fire as a minimum requirement for the .50 cal gun. We can't do that with the 20, so we give them 200 rounds. The 20 is lethal enough to get far more results out of that 200 rounds than the .50 ever will out of 400 rounds."

From: "USN Report of Joint Fighter Conference NAS Patuxent River". (October 1944)

From hindsight we know that the 50-cal gun had not reached it's peak 1944; M3 entered service next year and offered about 50% increase in fire power. Infact there was allready a 1100rpm version of the original M2, twice the rate of the original MG53-2, in production three years before US entered war as you probably know. The design had some potential left, USAF was just slow to utilize it.

However, as noted above, I agree that the cannons had great advantages over the M2 but it's not the point of this discussion.

[Stewart]

Infact I agree with you that the USAF might have done better by adopting a cannon like the Hispano or the MG 151. However, it's not the point discused here. I dispute this idea! That the USAF shot down many more Axis planes than any of, or possably all of the other Allied powers is not open to dispute! Given that the allies planes all had about the same performance Vs their Axis opponents, yet scored so much better, both in absolute numbers and as a ratio of the number of missions representing opportunity.
That the Germans chose to use guns not well suited to shooting fighter planes, but which were much better at bombers is a politicle desision.