Armor Penetration - 20mm vs. .50 cal.

[HoHun]

Hi Grame,

>I guess you could call it that! The manual belonged to my father when he was training to be an air gunner in 1944.

Nice bit of family history there! Looks like very professional training material, probably a sign they were really training an army of gunners! Proper typesetting, illustrations, coulored plates - everything one could wish for. Does it come with a date to see if it's "old" peacetime material, or whether it's a wartime edition?

Regards,

Henning (HoHun)

 

[Jank]

Magister do you still have those armorer manuals that were used to sight in the mounted guns? I thought they had some of that information that's needed to calculate the spread of the pattern and drop.

I'm sending you a PM.

 

[tomo pauk]

The weight of a projectile is a component of of sectional density (SD) which is a component of ballistic coefficient (BC). I just skipped to BC.

Ballistic coefficient: BC=SD/i (i is the form factor [shape] of a bullet).

Totally agree

I stand corrected

 

[davparlr]

You're passing this judgement from a implicit assumption on when the decision to adopt cannon would have had to be made, and this assumption obviously is "too late". Assume "in time" for a change, and your conclusion will be different.

Regards,

Henning (HoHun)

Well, I think we have butted heads enough. No opinions have changed I'm sure. Here is a parting shot.

I think the British voted with me in the Fall of 1943. Having experience with both the 20mm, in its British aircraft, and the 50 cal, on the P-40 Kittyhawks, F4Fs, and P-51As, they decided not to modify their F4Fs, F6F, and P-51B with 20mms. This certainly would not have been difficult for the P-51B, which had already been built to support the 20mm and, indeed, the XP-51B#2 had already been flown with four 20mms, and probably not for the other two. I suspect this decision affected well over a 1000 aircraft for the British. It is not likely that they would support your contentions regarding the 50 cal's significant impact on performance and lack of effectively and then would not have ordered from the factory, or installed on their own, 20mms in these aircraft, which they were going to fly against very formidable forces in ETO. It is obvious that, for some reason or another, the RAF thought that the modifying these aircraft to 20mm was not worth the trouble, which is the exact decision the USN made in 1940 through 1945. The USAAF never felt that there was any need at all for the 20mm in fighters until post Korean War. Certainly for the USAAF and USN, the decision was made on the flightline and the fleet, not by the table pushers. The opinion of the guy in the cockpit, putting his life on the line, always outweighs the opinion of the analyst, as it should be.

By 1939-40, the US had already established the 50 cal as its primary weapon system for fighters and, at that time there was no reason to change from a proven weapon system to one that was still developing, nor was their an established reason to do otherwise. The British didn't implement the 20mms till mid-41.

The concept of considering a weapon a failure based on lack of firepower is strange to me. The US method of warfare was to win with logistics; out produce and out support the enemy. In order to achieve this, compromises were made in products to support manufacture and logistics in addition to weapon effectivity. If you start claiming that weapons that were not optimized for weapon effectivity were failures, you would have a long list of American weapons, all of which, may have contributed to losses in the short run, but saved lives in the long run by shortening the war due to quantities available. By just about general consciences, American productivity, not their weapon superiority, was the overwhelming reason the Allies won the war. The 50 cal fit very well into this strategy.

You can have the last say.

 

[HoHun]

Hi Davparlr,

>I think the British voted with me in the Fall of 1943.

I don't think the British had any choice in the fall of 1943 - beggars aren't choosers. Pressure towards standardization was considerable, and the British happily went along with it because that was the way to get the US to make some specifically British requirements part of the standard too. There was no middle ground - it would have been either all Mustangs with 20 mm cannon, or all Mustangs with 12.7 mm machine guns. No way get the USAAF to agree to cannon, so - machine guns for the RAF.

What the British really thought about the Mustang's 12.7 mm machine guns' firepower is explicitely stated in the report I quoted above - "very little compared with the Spitfire".

The decision to accept the 12.7 mm armament was a strategic one and ran counter to better knowledge of the tactical value of the machine-gun battery expressed in the technical reports.

>The USAAF never felt that there was any need at all for the 20mm in fighters until post Korean War.

Actually, Project GUNVAL proved that the USAF felt the need very keenly right in the middle of the Korean war when their 12.7 mm machine guns proved lacking.

>The opinion of the guy in the cockpit, putting his life on the line, always outweighs the opinion of the analyst, as it should be.

Quite the opposite - the British virtually invented Operations Research in WW2 because they appreciated the input of the "table pushers", and their success certainly proved them right. You'll find nothing but admiration for the "boffins" among British servicemen who witnessed their efforts, if you look past the good-humoured jokes about their different frames of reference. The "guy in the cockpit" probably didn't even know that he could have had the same firepower for his P-47 at 500 lbs less weight - or did you ever find the 12.7 mm machine gun praised with words to the effect "worth every of the 500 lbs of their extra weight and more"?

>The concept of considering a weapon a failure based on lack of firepower is strange to me.

Just contemplate the number of pilots that were lost through lack of performance, lack of manoeuvrability or lack of fuel brought about by the 500-something pounds of extra weight incurred by the overweight and underpowered 12.7 mm machine guns. If a weapon needlessly weighs you down enough to get you shot down, it has failed you. If the extra weight is inevitable, nothing one could have done, but if it's result of poor technology ... well, someone screwed up somewhere.

>If you start claiming that weapons that were not optimized for weapon effectivity were failures, you would have a long list of American weapons, all of which, may have contributed to losses in the short run, but saved lives in the long run by shortening the war due to quantities available.

Ignoring other weapons which I never mentioned, you statement would only be true if the American industry would have been incapable of providing the required number of cannon after the decision to adopt cannon would have been made in time to introduce them successfully. As the US failed to make this decision, they naturally ended up with an inferior weapon, but you're again ignoring the possibility that such a decision could have been made early enough to avoid all the failures that historically surrounded the US adoption of the Hispano cannon.

The numbers argument doesn't really cut it anyway since one cannon could have replaced about three machine guns, and with a timely ramp-up of production, there would have been no "quantities unavailable" like your argument implies. The "arsenal of democracy" could hardly be overtaxed with producing a couple of thousand cannon when it was capable of producing an abundant number of obsolete machine guns.

Regards,

Henning (HoHun)

 

[Clay_Allison]

Hi Davparlr,

>I think the British voted with me in the Fall of 1943.

I don't think the British had any choice in the fall of 1943 - beggars aren't choosers. Pressure towards standardization was considerable, and the British happily went along with it because that was the way to get the US to make some specifically British requirements part of the standard too. There was no middle ground - it would have been either all Mustangs with 20 mm cannon, or all Mustangs with 12.7 mm machine guns. No way get the USAAF to agree to cannon, so - machine guns for the RAF.

What the British really thought about the Mustang's 12.7 mm machine guns' firepower is explicitely stated in the report I quoted above - "very little compared with the Spitfire".

The decision to accept the 12.7 mm armament was a strategic one and ran counter to better knowledge of the tactical value of the machine-gun battery expressed in the technical reports.

>The USAAF never felt that there was any need at all for the 20mm in fighters until post Korean War.

Actually, Project GUNVAL proved that the USAF felt the need very keenly right in the middle of the Korean war when their 12.7 mm machine guns proved lacking.

>The opinion of the guy in the cockpit, putting his life on the line, always outweighs the opinion of the analyst, as it should be.

Quite the opposite - the British virtually invented Operations Research in WW2 because they appreciated the input of the "table pushers", and their success certainly proved them right. You'll find nothing but admiration for the "boffins" among British servicemen who witnessed their efforts, if you look past the good-humoured jokes about their different frames of reference. The "guy in the cockpit" probably didn't even know that he could have had the same firepower for his P-47 at 500 lbs less weight - or did you ever find the 12.7 mm machine gun praised with words to the effect "worth every of the 500 lbs of their extra weight and more"?

>The concept of considering a weapon a failure based on lack of firepower is strange to me.

Just contemplate the number of pilots that were lost through lack of performance, lack of manoeuvrability or lack of fuel brought about by the 500-something pounds of extra weight incurred by the overweight and underpowered 12.7 mm machine guns. If a weapon needlessly weighs you down enough to get you shot down, it has failed you. If the extra weight is inevitable, nothing one could have done, but if it's result of poor technology ... well, someone screwed up somewhere.

>If you start claiming that weapons that were not optimized for weapon effectivity were failures, you would have a long list of American weapons, all of which, may have contributed to losses in the short run, but saved lives in the long run by shortening the war due to quantities available.

Ignoring other weapons which I never mentioned, you statement would only be true if the American industry would have been incapable of providing the required number of cannon after the decision to adopt cannon would have been made in time to introduce them successfully. As the US failed to make this decision, they naturally ended up with an inferior weapon, but you're again ignoring the possibility that such a decision could have been made early enough to avoid all the failures that historically surrounded the US adoption of the Hispano cannon.

The numbers argument doesn't really cut it anyway since one cannon could have replaced about three machine guns, and with a timely ramp-up of production, there would have been no "quantities unavailable" like your argument implies. The "arsenal of democracy" could hardly be overtaxed with producing a couple of thousand cannon when it was capable of producing an abundant number of obsolete machine guns.

Regards,

Henning (HoHun)

I think telling Oldsmobile to mass produce corrected H.S.404s instead of the dubious M4/T9 37mm blunderbuss would have had a good cannon rolling off the line in no time.

 

[HoHun]

Hi Clay,

>I think telling Oldsmobile to mass produce corrected H.S.404s instead of the dubious M4/T9 37mm blunderbuss would have had a good cannon rolling off the line in no time.

Good point - the initial reliability problems of the M4 might have contributed to turning the USAAF away from cannon, I'd imagine.

By the way, whatever happened to the 23 mm cannon initially used in the P-38, for example? Was it a Madsen copy that couldn't be licensed as intended after Germany occupied Denmark?

Regards,

Henning (HoHun)

 

[Clay_Allison]

Hi Clay,

>I think telling Oldsmobile to mass produce corrected H.S.404s instead of the dubious M4/T9 37mm blunderbuss would have had a good cannon rolling off the line in no time.

Good point - the initial reliability problems of the M4 might have contributed to turning the USAAF away from cannon, I'd imagine.

By the way, whatever happened to the 23 mm cannon initially used in the P-38, for example? Was it a Madsen copy that couldn't be licensed as intended after Germany occupied Denmark?

Regards,

Henning (HoHun)

You'd think we'd just license it ourselves and worry about paying Madsen after the war.

 

[davparlr]

You can have the last say.

I guess I lied.

I don't think the British had any choice in the fall of 1943 - beggars aren't choosers. Pressure towards standardization was considerable, and the British happily went along with it because that was the way to get the US to make some specifically British requirements part of the standard too. There was no middle ground - it would have been either all Mustangs with 20 mm cannon, or all Mustangs with 12.7 mm machine guns. No way get the USAAF to agree to cannon, so - machine guns for the RAF.

I think this statement is unsupportable. The British were not shy in upgrading American equipment in order to improve them per their concept, which were usually good. For instance, they upgraded the P-51 with the Malcolm hood to improve visibility, did their own Merlin upgrade trials, and they also added rocket launchers. They also had no problem upgrading the Sherman tank, which was really a "standard" weapon, with a much more powerful gun because the 75 mm was not powerful enough. You are asking us to think the British Army could make the Firefly out of the standard Sherman (they built about 2100 of them) but the RAF and the RN was not able to upgrade the P-51, F4F, and F6F for the same reason. I do not believe that is reasonable argument.

What the British really thought about the Mustang's 12.7 mm machine guns' firepower is explicitely stated in the report I quoted above - "very little compared with the Spitfire".

Remember that was with the four gun P-51B. Also note that they said it was "very little compared to the Spitfire", they did not say it was insufficient, which I am sure they would have said had they thought so. Also, here is a quote from "Mustang" by Robert W. Gruenhagen, which seems to be a pretty good book. This is a reference to the P-51B operations of the 2nd Tactical Air Force of the British Air Arm after receiving the plane.

"Soon after the aircraft was put into service, several reports were sent to Boxted concerning the deficiencies discovered with the use of the airplane. Propeller seal leaks, gun jamming, engine oil breather problems and oxygen system failures were the main problems encountered."

There doesn't seem to be a note about the ineffectivity of the 50s, and the British were also quite familiar with the 20mms. If they agreed with you, you would have thought they would have said something like "We need more firepower".

The decision to accept the 12.7 mm armament was a strategic one and ran counter to better knowledge of the tactical value of the machine-gun battery expressed in the technical reports.

But not supported by tactical reports.

Actually, Project GUNVAL proved that the USAF felt the need very keenly right in the middle of the Korean war when their 12.7 mm machine guns proved lacking.

I didn't mean to imply that the need was not felt during the war, only that the 20mm was not implemented until after the war for the AF.

Quite the opposite

I can assure you that during 29 years of design engineering and managing, I have had many a sound argument lost to test pilots/warfighters. They carry a lot of weight, especially when someone wants to change something they have that works. I must admit, however, if I had won one my arguments, we might have lost a B-2. I didn't really fight very hard and we settled on a happy compromise, but that is another story. By the way, I won almost all of my positions, but I had to win over the pilots.

The "guy in the cockpit" probably didn't even know that he could have had the same firepower for his P-47 at 500 lbs less weight - or did you ever find the 12.7 mm machine gun praised with words to the effect "worth every of the 500 lbs of their extra weight and more"?

I bet those Brits in the P-51 understood all about the 20s and were still silent. It is also interesting to note that at the 1944 Fighter Conference, that there were quite a few RAF and RN type and the biggest comment they had when discussing the 20mm vs the 50 cal, was "they liked the 20mm", but none from the RN guys stated their desire for the weapon or the weakness of the 50 cals. If they were as passionate as you are about the advantages of the 20mms, you would have thought they would have stated so when asked at a conference comparing operational performance of fighter weapons systems.

Just contemplate the number of pilots that were lost through lack of performance, lack of manoeuvrability or lack of fuel brought about by the 500-something pounds of extra weight incurred by the overweight and underpowered 12.7 mm machine guns. If a weapon needlessly weighs you down enough to get you shot down, it has failed you. If the extra weight is inevitable, nothing one could have done, but if it's result of poor technology ... well, someone screwed up somewhere.

All you have is contemplation. You have never provided information such as kills/engagement, sorties per kill, or even probability of kill comparison of a three second burst in multiple scenarios and on average. These are the type of variables that must traded off against production line interruptions, delivery delays of critical assets, logistic cost, etc., for a decision maker to overturn or argue to change the desires of the warfighter who have not been complaining. All aircraft have compromises that affect performance in some manner. You have no idea how many lives would have been saved, if any.

You're comment that ""probability of strikes" is completely secondary to the "probability of kill"" is confusing. If you have a Pkill/strike is 100% and your Pstrike is 0, your probability of kill is 0. It looks to me that the probability of strike is vital to probability of kill, not secondary.

but you're again ignoring the possibility that such a decision could have been made early enough to avoid all the failures that historically surrounded the US adoption of the Hispano cannon.

I did not ignore it. I stated before that it wasn't until late 1940 before the British started to update to the 20mm. At that time, the US had multiple platforms in production and in development. In addition, they had established production lines, logistics and maintenance systems. Also, there was no operational report that the 50 cals were not effective. I am sure that there was not a production facility ready to produce the thousands of canons per month required to supply the rapidly increasing US production capability. Any available production facility, such as an automobile plant, would require tools to be manufactured and personnel to be trained and supply line established. All of this would have taken months to get up to speed. The aircraft builders would have to design and build tools, establish supplies, and pull workers off the production line to train in installing the new equipment, which would have delayed aircraft production by at least three to six months, when aircraft quantities were critical, especially to the British (most likely, the F4F-4 with 20mm would not have been available for the battle of Midway, which they barely made anyway). All of this with no indication of the effectivity of the 20mms, or whether the 20mms being built were going to work, and, again, NO indication that the 50 cals were not effective, because they were.

The numbers argument doesn't really cut it anyway since one cannon could have replaced about three machine guns, and with a timely ramp-up of production, there would have been no "quantities unavailable" like your argument implies. The "arsenal of democracy" could hardly be overtaxed with producing a couple of thousand cannon when it was capable of producing an abundant number of obsolete machine guns.

Numbers was never a problem except in start-up time. If the decision was made in 1938, I am sure the 20mm would have been incorporated flawlessly, but it wasn't.

The silence of the British when addressing the 50 cals on American fighters is deafening, there seems to have been very little complaint.

By the way, I saw that the 2nd Tactical Air Force flew P-51III and Spitfire IX at the same time. It would be interesting and informative to this argument to learn the kills/engagement of each. The P-51III was somewhat similar to the Spit IX, but their mission may have been different.

 

[HoHun]

Hi Davparlr,

>I think this statement is unsupportable.

If you look at your own post with a bit of critical distance, you'll discover that all you do yourself is to make unsupported claims.

Below, I've listed some references that will fill you in on what you apparently have missed so far. If you have any comments on the referenced stuff, that would be helpful and might get us out of the repetition cycle we're currently in.

Oh, and I'd like to suggest that it would be better if you'd support your claims, too.

Stuff like can be considered unsupported:

>If they agreed with you, you would have thought they would have said something like "We need more firepower".

Stuff like this would seem supported:

"In tactical report XY, the RAF said 'We have enough firepower".

Accusing me of unsupported statements when you have not a shred of positive evidence for anything you say looks regrettably like double standards.

>You have never provided information such as kills/engagement, sorties per kill, or even probability of kill comparison of a three second burst in multiple scenarios and on average.

See my post #137, "Don't fool yourself".

>production line interruptions

See my post #155, "lead time".

>You're comment that ""probability of strikes" is completely secondary to the "probability of kill"" is confusing.

See my post #99, "Pk_total".

>If the decision was made in 1938, I am sure the 20mm would have been incorporated flawlessly, but it wasn't.

Exactly. That's where the US failed. That's what my post #155, "lead time", already pointed out.

I'm afraid large parts of our disagreement was entirely superfluous as it stemmed from different assumptions, but I had tried to point that out as early as in post #137, "lead time".

Regards,

Henning (HoHun)

 

[renrich]

Interesting discussion or debate. Lots of ifs and buts. What do we know for certain? We know that the US began to ramp up design, development and production of aircraft in 1940. We know that the US built and deployed more than 100000 fighters during WW2. We know that most of those fighters deployed with the 50 BMG as the primary weapon. We know that most of the bombers deployed with the 50BMG as their defensive weapon. We know that the US had to transport the aircraft, weapons and all support material and personnel over thousands of miles of ocean to all parts of the globe in order to get into action. We know the other combatants largely did not have that problem. We know that essentially, the only purpose in building and deploying a fighter was to be able to bring those four,six or eight 50 BMGs to bear on the enemy. We know that, by the end of the war, the enemy air forces had been swept from the air, the majority of the damage being done by the various units of the AAF, USN and USMC. We know that the 50 BMG, whether used by a fighter, bomber, ship, AFV, jeep, truck or infantryman was highly effective against fighters, bombers, ships, AFVs, transport or any enemy personnel not protected by adequate armor or fortifications. The correct decision by the US as far as weaponry is concerned seems to have been made. The proof of the pudding is in the eating.

 

[Jabberwocky]

And the US Army also won the majority of its land battles with the BAR as its primary infantry automatic weapon and the Sherman as its main tank. But, you'll find few people that will argue that it wouldn't of been better served by a true light machine gun or a better armed and armoured tank.

I think that the "It must of been worked because we won and shot down lots of stuff with it" argument misses the main crux of the debate.

Just because the .50 was effectively used, doesn't mean that it was as effective as another weapon system, such as the Hispano, could of been.

Personally, while the pilots may of been happy with it, I think that the USAAF was never fully satisfied with the M2 as an aerial weapon. It knew that there were other weapons better suited to aerial combat, which could give more firepower for less weight.

Otherwise it wouldn't of mucked about with the various 37 mm, 20 mm and 0.60 cal weapons through the war, nor bothered developing the faster firing M3.

But, it used what it had, well, in the situation it was give.

 

[Magister]

"few people that will argue that it wouldn't of been better served by a true light machine gun"

Curious what potential replacement do you think would have been viable?

 

[Glider]

"few people that will argue that it wouldn't of been better served by a true light machine gun"

Curious what potential replacement do you think would have been viable?

Bren Gun?

 

[BombTaxi]

The Bren would indeed have been a good replacement for the BAR, or the French FM.24, something that was a machine gun as opposed to an automatic rifle. The BAR had no real sustained fire capability, making it less effective as an SAW. Ideally, all the Allied nations could have done with a weapon along the lines of the MG34 and 42 LMGs used by the Germans. These were proper MGs, with sustained fire capability, yet portable within an infantry squad. Much better than Bren or BAR, but much more costly as well, I would suspect.

 

[Magister]

The Bren was much heavier, unwieldy and fired a less powerful cartridge. The BAR was a good gun.

 

[BombTaxi]

The BAR was a very good gun. But it was essentially unsuited to the role it was deployed in, having no sustained fire capability. The BAR was intended as an automatic personal weapon - almost a proto-assault rifle. In that context, you wouldn't use an AK74 or M16 as a SAW, would you? They're both very good guns, but not in that role.

EDIT: I think you claims about the deficiencies of the .303 cartridge are moot points. If. for arguments sake, the US had adopted the Bren, they wouldn't have used .303 ammo - they would have had a new version chambered to .30-06 to avoid having to deliver two calibres of small arms ammo to infantry units.

 

[Magister]

Assault rifles, by definition, are rifles that are lighter than battle rifles that fire intermediate cartridges. The BAR was not "almost" even close to that. The M1 Carbine, for the Americans, would be an appropriate comparison.

Yes, the BAR had a 20 rd. capacity vs. the Bren's 30 rd capacity. I still say that its smaller size, far less weight (the Bren was 1/3 heavier than the BAR) and ability to be wielded more easily in combat were important attributes as well. The Bren's larger size and much heavier weight made it less suitable for rapid, mobile small squad operations.

Incidentally, the M249 is roughly the same weight as the BAR and also far smaller than the Bren. It does have enormous capacity, however.

 

[Glider]

I don't think that there is any doubt that both were first class weapons, the difference being that one is an automatic rifle and the other a light machine gun.
The biggest difference being that the Bren is better at longer bursts due to the ability of the barrel to be quickly changed, plus the bigger magazine.

I didn't realise that there was such a difference in the weight of the weapons. I have the BAR weighing in at 19 lb (empty) and the Bren 23.5lb (Loaded), 21 lb (empty). There were lighter versions of the Bren but I believe the above figures were the norm.

Given the small increase in weight to be worthwhile considering the extra flexibility.

 

[Magister]

I stand corrected. There is not nearly the weight difference that I indicated.