The real combat history of the P-39 Airacobra in the Pacific (1 Viewer)

[Shortround6]

They were certainly flying and fighting over 10,000ft in WW I. Even 15,000ft.
However there were primitive oxygen systems in use in WW I. Like a tube held between the teeth and turning the valve by hand.

I could be very wrong about this particular thought.
Is there some sort of time duration that came into play?
Like is 10 minutes at 15,000ft the same as 20 minutes at 12,000ft?
We do know that all pilots did not have the same tolerance for altitude and even that might vary from day to day (health).
Cruising around at 8-9,000ft for a 1/2 hour may actually hurt pilots' tolerance vs steady climb into the teens.
The longer a pilot/crew tries to fly at over 10,000ft the more pronounced the effect?

 

[Steamed_Banana]

All fair questions. You can actually acclimate to high altitude, climbers do so. Some people have climbed Everest without oxygen. But I think that is pretty rare. Maybe if their base was at 5,000 feet to start with that might help, but they are starting from a very thick air down right at sea level.

 

[MIflyer]

The 20mm is generally better at least for air to air isn't it? More accurate, better range, more ammunition...

Jamming was all too frequent with the 37MM. When the USAAF told the RAF that the P-39's cannon could crack German tanks, the Brits took a P-39, set it up on the gunnery range and tested it against a German tank. First thing they found was that the 37MM would jam after the first round. A grizzled old RAF armorer set to work and found that the ejection arm was too long. They sawed it off a bit and got it working. Why they did not figure that out in the USA I have no idea. The second thing the RAF found is that the 37MM would not crack a German tank, while the Vickers 40MM on the Hurricane IID would. The 37MM was an air to air weapon with a velocity too low to penetrate tank armor. The 37MM used on the Stukas was an AA gun and had proper velocity.

One book written by a P-39 pilot who flew in the Solomons explained the jamming problem with the 37MM. He said it worked fine as long as you had POSITIVE G Loads. In a dive, you usually have negative G loads. So the thing to do was to not fire right after you started the dive but instead dive a little too steeply and then pull up onto the target just before firing the cannon, to have positive G loads.

I think an underappreciated aspect of the mixed .50,.30, and 37MM armament is that the trajectory of each of the three rounds was different. If you were dead nuts level 100 feet behind an airplane you could hit him with all the rounds. If you were diving at a ground target and walking the rounds through it, Okay. But trying to do deflection shooting against an aerial target, leading the other airplane during a curved approach, made it too hard.

It appears that the P-39D-1 was built so that the guys equipped with the P-400 could have replacement airplanes with the same armament to help with logistics. The 20MM was used on the P-39 and P-38 and initially with some A-20, where it was soon abandoned in favor of .50 cal. That same ammo was used for ground based 20MM, mainly on USN ships, and that no doubt helped with the supply situation. I had wondered if the P-39D-1 were P-400 refurbed to US standards but the Profile says they were produced under a USAAF order.

An article by a pilot who ferried P-39 and P-63 up to AK says that the P-39Q with the underwing guns shuddered and shook more than the earlier models when going over 300 MPH.

The Profile mentions a case where a P-39 scored kills with all the machine guns jammed and just the 37MM working, a couple of Rufe seaplanes in the Aleution Islands. That was a real achievement since the 37MM had a very slow rate of fire, about 150 RPM, which sounds fast but is not.

I wonder what the Soviets did about the 37MM? I have a book on the Soviet experience that I have not read yet. In any case they must have liked it because they put a 45MM on some of their YAK-9's and used 37MM on the Mig-15.

 

[MIflyer]

Like is 10 minutes at 15,000ft the same as 20 minutes at 12,000ft?

There are FAA limits on how long you can stay above 10,000 ft with out supplementary oxygen; I think it is 30 min for aircrew, longer for passengers.

And it depends on the person. Some people take off their mask at 20,000 ft and pass right out. Some do not seem to be affected. I started getting woozy after a while but did not pass out. The thing that struck me was that I could not feel the difference in the air. I had assumed that at 20,000 ft you are at 2.9 PSI rather than 14.7 SPI and you could tell then difference by waving your hand. The crew in the chamber saw me trying to feel air molecules and probably assumed I was out of it.

If you smoke you probably get in trouble fast. On some of the P-51 missions to Germany they did not have enough oxygen to cover the whole mission but Blakeslee told them to tough it out.

The first thing affected, though, is your eyesight. Standard USAF practice is use 100% oxygen from the ground up at night.

 

[Shortround6]

That same ammo was used for ground based 20MM, mainly on USN ships, and that no doubt helped with the supply situation.

Both right and wrong. The Oerlikon and Hispano guns used different cartridge cases pf different shapes, especially the rims.
However, they used the same projectiles. Not any good at using end of the supply chain, but made things easier at the factory end.

But trying to do deflection shooting against an aerial target, leading the other airplane during a curved approach, made it too hard.

there is not only the difference in trajectory but the difference in time of flight. Not bad at 100-150 meters but could be over 0.1 seconds at 300 meters? worse at longer ranges.

Difference between the US 37mm aircraft gun and the British 2pdr was that the US 37mm projectiles weighed 608 grams, AP might have been a bit heavier. 2pdr was fired at nearly the same velocity but the AP projectile weighed 1130 grams. The weight gave it a lot of "smash"

 

[special ed]

Our indoctrination to the oxygen chamber showed individual variations. Following the instructions during orientation, once in the chamber, I watched my fingernails and put on oxygen when they turned deep blue although I could still function. As I looked around, perhaps half of the twelve were sagging & sleepy. One guy, a barrel chested man with a body builder shape, sat smiling after all of us were on oxygen. Finally, the sergeant called a stop, but the last man was still functioning completely.

 

[Steamed_Banana]

Jamming was all too frequent with the 37MM. When the USAAF told the RAF that the P-39's cannon could crack German tanks, the Brits took a P-39, set it up on the gunnery range and tested it against a German tank. First thing they found was that the 37MM would jam after the first round. A grizzled old RAF armorer set to work and found that the ejection arm was too long. They sawed it off a bit and got it working. Why they did not figure that out in the USA I have no idea. The second thing the RAF found is that the 37MM would not crack a German tank, while the Vickers 40MM on the Hurricane IID would. The 37MM was an air to air weapon with a velocity too low to penetrate tank armor. The 37MM used on the Stukas was an AA gun and had proper velocity.

One book written by a P-39 pilot who flew in the Solomons explained the jamming problem with the 37MM. He said it worked fine as long as you had POSITIVE G Loads. In a dive, you usually have negative G loads. So the thing to do was to not fire right after you started the dive but instead dive a little too steeply and then pull up onto the target just before firing the cannon, to have positive G loads.

I think an underappreciated aspect of the mixed .50,.30, and 37MM armament is that the trajectory of each of the three rounds was different. If you were dead nuts level 100 feet behind an airplane you could hit him with all the rounds. If you were diving at a ground target and walking the rounds through it, Okay. But trying to do deflection shooting against an aerial target, leading the other airplane during a curved approach, made it too hard.

It appears that the P-39D-1 was built so that the guys equipped with the P-400 could have replacement airplanes with the same armament to help with logistics. The 20MM was used on the P-39 and P-38 and initially with some A-20, where it was soon abandoned in favor of .50 cal. That same ammo was used for ground based 20MM, mainly on USN ships, and that no doubt helped with the supply situation. I had wondered if the P-39D-1 were P-400 refurbed to US standards but the Profile says they were produced under a USAAF order.

An article by a pilot who ferried P-39 and P-63 up to AK says that the P-39Q with the underwing guns shuddered and shook more than the earlier models when going over 300 MPH.

The Profile mentions a case where a P-39 scored kills with all the machine guns jammed and just the 37MM working, a couple of Rufe seaplanes in the Aleution Islands. That was a real achievement since the 37MM had a very slow rate of fire, about 150 RPM, which sounds fast but is not.

I wonder what the Soviets did about the 37MM? I have a book on the Soviet experience that I have not read yet. In any case they must have liked it because they put a 45MM on some of their YAK-9's and used 37MM on the Mig-15.

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All very interesting.

I think most of the larger caliber guns, including in particular the US 12.7mm and Hispano 20mm were having a lot of problems with jamming in the early years of the war, some of which were resolved in several stages starting in mid 1942 and continuing as late as 1944.

 

[SaparotRob]

Our indoctrination to the oxygen chamber showed individual variations. Following the instructions during orientation, once in the chamber, I watched my fingernails and put on oxygen when they turned deep blue although I could still function. As I looked around, perhaps half of the twelve were sagging & sleepy. One guy, a barrel chested man with a body builder shape, sat smiling after all of us were on oxygen. Finally, the sergeant called a stop, but the last man was still functioning completely.

Years ago I was watching a Public Broadcasting Corporation show that showed the effects of oxygen deprivation on performance. I don't remember it exactly but someone was cutting pieces for structural work.
"I cut it three times and it's still too short."

 

[special ed]

That's exactly the way I build balsa models. I have for 70 years.

 

[bf109xxl]

I wonder what the Soviets did about the 37MM? I have a book on the Soviet experience that I have not read yet. In any case they must have liked it because they put a 45MM on some of their YAK-9's and used 37MM on the Mig-15.

I have a hypothesis: the Soviets assigned Cobras mainly to regiments with a high percentage of experienced pilots. That is why the M4, despite its mediocre ballistics, proved highly effective in combat. The N-37 on the MiG-15, on the other hand, had a much higher rate of fire, and the muzzle velocity was remarkably higher as well. The effectiveness of the NS-37 on Yaks and Ilyushins is still a matter of debate, but it is clear that it was not high. The question is whether it was completely abysmal or more or less acceptable.

 

[MIflyer]

the Soviets assigned Cobras mainly to regiments with a high percentage of experienced pilots.

Perhaps, but then the Soviets, faced with lots of inexperienced pilots, which had to be the case to some degree, may have emphasized the "Stick your gun barrels up his arse before you open fire." approach.

As for the 20MM, when the first F4U with four 20MM went into combat the USMC found that the guns jammed at high altitudes. Supposedly the reason given was that the air war in the Pacific was considered to be a low altitude affair and so they skipped the high altitude tests to speed getting the guns into combat.

A friend of mine says that they solved the problem by giving the 20MM rounds a dip in hot wax before loading them in the aircraft.

 

[Steamed_Banana]

I have a hypothesis: the Soviets assigned Cobras mainly to regiments with a high percentage of experienced pilots. That is why the M4, despite its mediocre ballistics, proved highly effective in combat. The N-37 on the MiG-15, on the other hand, had a much higher rate of fire, and the muzzle velocity was remarkably higher as well. The effectiveness of the NS-37 on Yaks and Ilyushins is still a matter of debate, but it is clear that it was not high. The question is whether it was completely abysmal or more or less acceptable.

Soviets also had a policy for fighter pilots of shooting from very short range, as in ~ 150 meters or less. I don't know how much pilots actually followed that but considering how few guns most Soviet fighters had by say, mid 1942, it may have been their best bet. At that kind of range, the 37mm may not be so bad, and the first shot or two may even hit.

I believe some Soviet units also did remove the wing guns from the P-39s, though clearly not all of them.

 

[Shortround6]

P-39s may or may not have better gun sights.
The P-39 gun was less than 1/2 as powerful as the Soviet NS-37 gun and some soviet pilots report using the NS-37 as a repeating gun (or very short bursts) and not full auto. Others may have tried full auto fire but severe recoil seems to have moved the gun/plane off target very quickly which may have canceled out the higher rate of fire.
The later 45mm gun was effective in highly skilled hands but it was never adopted for true mass production. In part due the high skill needed to use it.
The post war N-37 gun used a shorter cartridge case with lower velocity to improve rate of fire and permit smaller size/weight.
The NS-37 may have been too much of a good thing. High power is only effective if it can be kept on target and doesn't break things on the firing aircraft.

 

[bf109xxl]

P-39s may or may not have better gun sights.
The P-39 gun was less than 1/2 as powerful as the Soviet NS-37 gun and some soviet pilots report using the NS-37 as a repeating gun (or very short bursts) and not full auto. Others may have tried full auto fire but severe recoil seems to have moved the gun/plane off target very quickly which may have canceled out the higher rate of fire.

The reasons are well-known and were analyzed in numerous sources citing soviet documents. The challenge consists in the assessment of the real combat performance on the frontline rather than under test conditions taking into account different pilot experience.

The later 45mm gun was effective in highly skilled hands but it was never adopted for true mass production. In part due the high skill needed to use it.

There was no significant difficulties with the mass production of the 111P (NS-45) - it differed very little from the production of the 11P (NS-37), and the gun passed all tests successfully. However, there was no need for it due to its weight, high recoil, low rate of fire, and limited ammunition capacity. The N-45 project for the Yak-9K, featuring reduced ballistics similar to the N-37, was canceled.

The NS-37 may have been too much of a good thing. High power is only effective if it can be kept on target and doesn't break things on the firing aircraft.

Frontline tests of the Il-2 equipped with the NS-37 did not reveal any significant advantages over the Il-2 equipped with the VYa. As for the Yak-9T with the NS-37, it was ill-suited for dogfights with fighters, although the Soviets used them primarily to escort ground-attack aircraft and bombers anyway - they didn't pay much attention to tactical considerations.

 

[MIflyer]

The later 45mm gun was effective in highly skilled hands but it was never adopted for true mass production.

And was it intended as anti-tank or and air-to-air weapon?

 

[MIflyer]

The 20mm is generally better at least for air to air isn't it? More accurate, better range, more ammunition...

Yes, but while there was a lot of planning for using the 37MM, there was not that much use other than P-39 and P-63. P-38 and A-26 were supposed to use it but did not, at least in combat. A-41 was equipped with four 37MM but they only built one of those.

 

[Marshall_Stack]

Soviets also had a policy for fighter pilots of shooting from very short range, as in ~ 150 meters or less. I don't know how much pilots actually followed that but considering how few guns most Soviet fighters had by say, mid 1942, it may have been their best bet. At that kind of range, the 37mm may not be so bad, and the first shot or two may even hit.

I believe some Soviet units also did remove the wing guns from the P-39s, though clearly not all of them.

I believe that the Russians just removed the .50 gun pods from beneath the wings on the aircraft that had it.

 

[Steamed_Banana]

I believe that the Russians just removed the .50 gun pods from beneath the wings on the aircraft that had it.

The Soviet also removed .30 caliber wing guns from the earlier P-39 variants in some units (not all). Golodnikov for example mentioned this in his interviews. This improved roll rate and probably turn rate a bit, reduced drag etc. Most Soviet aircraft didn't have wing guns, except other Lend-Lease types like the Kittyhawk, Spitfire, and Hurricane. So most pilots were not used to dealing with convergence etc. And some of these had some of their wing guns removed as well (some Soviet units removed all the wing guns from the Tomahawk / Hawk 81 types for example, relying only on the two 12.7mm nose guns).

Having had some difficult experiences with other Lend Lease types, especially to do with maintenance, the Soviets did a very thorough workup with their P-39s for ~ three months prior to putting them into combat. They made some changes (lots of those minor things like little valves and clips and such that Shortround mentioned, but also things like adding drains for all fluids for the winter time) and they adapted tactics specifically for this aircraft. This is why some of the units equipped with them were doing very well right out of the gate. Important to note that this was not all units.

The Soviets had also already adopted the tactic of shooting from close range, as I noted, so this method which was probably most suitable for the P-39 was already familiar, and many squadrons which switched to P-39 were (somewhat elite, or at least successful) Guards units etc. who were already very familiar with 'twitchy' aircraft like the I-16, MiG 3, or LaGG-3, so they had enough experience to fly these without necessarily falling into dangerous spins etc.

 

[bf109xxl]

And was it intended as anti-tank or and air-to-air weapon?

It was originally intended to use the 45-mm gun against _heavy_ German armored vehicles - incidentally, as many as three gun designs (by Nudelman, Shpitalny, and Grabin) were entered in the competition. But as was often the case with the Soviets, in reality, the Yak-9k was used to escort ground-attack aircraft and bombers in more than 80% of its sorties. Another interesting fact: the BT-45 AP shell for the 45-mm gun demonstrated worse armor penetration than the BT-37 for the 37-mm gun. Such are the paradoxes of Soviet aviation.

 

[Shortround6]

And was it intended as anti-tank or and air-to-air weapon?

As noted by bf109xxl there are several paradoxes.

Take the 37x198mm cartridge case, shorten it slightly to 186mm, neck it out 45mm and stuff heavier projectiles in it.
At best you have about the same amount of propellant, at worst??
For HE ammo the shell weight went from 735g to 1065g AP was ???
But velocity dropped from 880ms to 780ms.
Western sources do not mention AP rounds which does not mean they didn't exist or were not planned.

the Soviet 45mm tank and AT guns used much heavier projectiles of both HE and AP. Not to say they couldn't have been modified (shortened).
But cutting away a 1450g projectile down to 1065g or close takes a lot of work.
The APCR projectile weighed about 870g but the projectile was about 300mm long, cutting down to fit inside the aircraft gun shell and still have much room for propellent?
Unless you get some really good AP design (tungsten core?) the 37mm looks like a better bet for punching though armor.