Armor Penetration - 20mm vs. .50 cal.

[HoHun]

Hi Demetrious,

>How on earth the Hispano's P_hit_round value can be "close" to the 12.7mm with less then half the number of rounds in the air, I would really, really like to know.

Look at my original formula:

Pk_total = P_hit_round * n_rounds * Pk_round

The number of rounds is a separate multiplier.

>In fact, I've heard a lot of reports of gun comparisons done by the US Army, US Navy, RAF, Fleet Air Arm, etc, on a few different websites.

Fine, post some links then. I can't work with hearsay.

>>As I provided all the numbers as well as the link, simple diligence in reading (and thinking) would have prevented this mis-representation of my position by a factor of more than two with regard to the difference to the Navy's figures.

>Did you call Glider an idiot too, or is that reserved just for me?

One more trolling question like that, and you'll find yourself on my ignore list.

>As for the rest of this, I think the primary objection most people have to your statements [...]

Speak for yourself, or will find yourself on my ignore list.

>Yes, and an air-to-air missile armed F4F would have enjoyed significant and undeniable advantages over a machine-gun armed F4F as well.

The obvious difference between cannon and air-to-air missiles in a Battle-of-Midway context is that one side was actually using cannon, while neither was using air-to-air missiles.

The only thing that keeps you from my ignore list for now is that I prefer to give you a chance to shape up.

I'll give you the opportunity to re-phrase your post into something polite or at least even remotely acceptable before I answer the rest of your points.

Kind regards,

Henning (HoHun)

 

[Glider]

Did you call Glider an idiot too, or is that reserved just for me?

To be fair Henning hasn't called me an idiot. He has accused me of having an alternative agenda, but not an idiot.

I do agree with Henning re the effectiveness of the 20mm compared to the 0.5 (but not to the degree of the difference) but believe that the 0.5 was good enough.

Our difference is about his calculations re the power of the weapons which I believe to be biased towards the chemical energy. For example, to accept that the figures prepared by Henning are approx 25-55% different to the USN and USAAF figures and not try to work out why they are so different seems rash. Certainly I would not accept that at work.

Unfortunately he is unwilling to discuss the topic. Without knowing exactly how the the figures are derived it cannot go any further.
For instance, if Henning is working on the basis that if one shell has twice the explosive (chemical energy) than another then it is twice as effective before factoring in the Kinetic Energy, then I believe that is likely to be wrong. However I don't know if that is how his calculations are prepared, he may or may not have covered this, I simply don't know.

 

[Demetrious]

Hi Demetrious,
The number of rounds is a separate multiplier.

Your phrasing made it sound like you were comparing a single Browning to a single Hispano, but you also said that the "Hispano battery is superior" so I'll just put it down to "lost in communication."

You said something about the "Rate of Fire" fallacy at one point, and now I'm not sure what you were referencing. But if you say you account for the ROF, that's fine. Your calculations revolve around a pure effective throw weight analysis, whereas my analysis starts with a consideration for the effective pattern density and hit distribution, and then whimpers in fear when asked to consider the myriad factors regarding ordinance effectiveness and effect. You probably thought I was criticizing your analysis of throw weight. I don't really see a problem with that- you say that the cannons put out more metal, and that's not really anything that anybody can deny.

Fine, post some links then. I can't work with hearsay.

Actually, I suspect much of it is heresay, which is why I am constantly confused as to what anecdotes to trust. This is percisely why I only raised the matter by extending the concerns raised by other, reliable posters, the most recent being Glider.

If you have Glider on ignore already, however, this could explain your attribution of these claims to me alone.

Speak for yourself, or will find yourself on my ignore list.

I am speaking for myself; it is an impression I have received also.

The obvious difference between cannon and air-to-air missiles in a Battle-of-Midway context is that one side was actually using cannon, while neither was using air-to-air missiles.

The Japanese Ho-99 cannon had markedly poor ballistic performance (although it should be noted that it had an amazingly light weight, for a cannon.) As I have noted before, poor ballistic performance can significantly complicate air-to-air gunnery, even at shorter ranges. This problem was magnified by the short firing duration of the Zero's cannons (8 seconds, about, if memory serves,) though this was a fault of the 60 round drums used for the cannons, and not any inherent fault of the weaponry. This firepower was needed, because the F4F was an amazingly tough aircraft- so much, in fact, that the 7.7mm guns of the Zero had great trouble downing them even when given a perfect shot and ample time (which few American pilots would sit around and afford them.)

Now, the Americans had the batteries of four .50 cal guns, with 33 seconds of firing time, (if I remember your numbers right,) and were up against very vulnerable aircraft. Their firepower was sufficient to destroy the enemy, (just as the Japanese cannon was sufficient to destroy American F4Fs,) but the .50 cals had a much longer firing duration then the opposing cannons, and superior ballistics which made gunnery easier.

For these reasons, I consider that engagement a wash. This is not to say, however, that Hispanos would not have been valuable, as they would have given the F4Fs guns with good ballistics and heavy firepower (the Hispano.) As it stood, though, I think the F4Fs in the Battle of Midway were on equal footing. Both combatants had guns that could reliably destroy their principal opponents.

I'll give you the opportunity to re-phrase your post into something polite or at least even remotely acceptable before I answer the rest of your points.

The only thing I said that could be remotely interpreted as being "impolite" was when I bristled at the implication that I was not "clear-thinking." The rest of my post was delivered with the same formal diction I prefer in such discussions.

In short, unless I re-write my last post to kow-tow to you in a most simpering fashion, you will refuse to answer the rest of my considerations. This is in addition to the many variables I raised several posts back, which you still have not addressed- not even to say that they are overly fine nitpicks with little bearing on the final analysis (which I still entertain as a valid answer to them.)

Everything considered, I am afraid that the potential for constructive discourse between us, both in this thread and future topics, is slim. In the interests of preserving the mostly-amiable atmosphere of this wonderful forum, I will engage in no further discussion with you. If my disassociation is not enough for you, then you may still deal with your ignore list as you see fit.

 

[HoHun]

Hi Demetrious,

You're on ignore now.

Kind regards,

Henning (HoHun)

 

[Clay_Allison]

You know, I think I know soemthing the U.S. could have done to make those H.S. 20mm cannons work.

As I understand it, their issue was headspacing. There are two ways to fix that. The obviuous way is to tighten up your manufacturing tolerances. We seemed not to be able to do that while the british succeeded.

There is, however, a quick fix. Replacing the 20mm cartridge with a rimmed version. There would be some issues with feeding to work out and the bolt face would have to be changed, but headspacing and mass production is the reason that the Soviet 7.62x54 is a rimmed cartridge, and part of the reason for the British .303 being rimmed.

A rimmed 20mm cartridge with the same case dimensions otherwise would be as easy a change to make as making a .30 cal Browning MG as .303 (somethign that was obviously done).

 

[Demetrious]

You know, I think I know soemthing the U.S. could have done to make those H.S. 20mm cannons work.

As I understand it, their issue was headspacing. There are two ways to fix that. The obviuous way is to tighten up your manufacturing tolerances. We seemed not to be able to do that while the british succeeded.

There is, however, a quick fix. Replacing the 20mm cartridge with a rimmed version. There would be some issues with feeding to work out and the bolt face would have to be changed, but headspacing and mass production is the reason that the Soviet 7.62x54 is a rimmed cartridge, and part of the reason for the British .303 being rimmed.

A rimmed 20mm cartridge with the same case dimensions otherwise would be as easy a change to make as making a .30 cal Browning MG as .303 (somethign that was obviously done).

Interesting!

A further question for you sir, since you are more knowledgeable about firearms then I- what made the M2 Browning so heavy? It has been my general impression that increasing rate of fire requires a lighter bolt assembly- but that, in turn, reduces the amount of power the gun can safely handle, and thus, cartridge power and muzzle velocity. Could there have been a way to lighten the M2 Browning, or increase ROF, without sacrificing its flat trajectory?

 

[renrich]

Probably not realistic to expect a cannon armed Wildcat to be operational by Midway even if a reliable cannon had been available. Having enough folding wing Wildcats(F4F4s) to stock each VF squadron on the 3 carriers was a problem and the gun installation that Grumman came up with for the F4F4 with the additional gun in each wing(because of British insistence) even with the familiar 50BMG was not satisfactory. During the Wildcat's lengthy gestation, if the USN and Grumman(and Vought with the Corsair) had been able to see into the future to the late 1940s, they undoubtedly would have tried to fit a reliable 20 mm to those AC. However, in 1940, the RAF appeared to be effective with the 303s and the 50BMG was many times more effective than the 303. The USN pilots liked the four gun battery with 400 rds each in the F4F3(once feed problems were reconciled) and it proved very effective.

 

[HoHun]

Hi Davparlr,

>Also, the British flew Mustang III and IVs with 50 cals. I looked to see if there were any complaints as they were familiar with 20 mm and could make a comparison. With my admittedly limited research ability, I found a complaint about the visibility from the Mustang III, but not a comment about the 50 cals.

Though Mike's ww2aircraftperformance is mostly focussed on performance, it also has some tactical trials strewn between.

This quote is from the Mustang III Tactical Trials:

"The fire-power consists of four .5 Browning's in the wings. This is very little compared with the Spitfire."

Mustang Tacical Trials

(In terms of total muzzle power, the Mustang III armament yields 1.14 MW firepower, while the Spitfire armament of two cannon and two 12.7 mm machine guns yields 2.69 MW firepower, confirming the laconic British statement.)

Here is another interesting quote from the US P-47C-1 Tactical Suitability Trials at Eglin Field:

"3. CONCLUSIONS:

It is concluded that:

a. The P-47C-1 is the best high altitude fighter aircraft now in production with regard to high speed, stability, pilot comfort, height and armament.

b. The rate of climb is not as good as desired, which fact limits its suitability as a medium altitude fighter and as an interceptor.

c. All weight in the structure and accessories not vital to operational use should be eliminated."

P-47C Tactical Trials

b) and c) both adress the question of excessive weight, and while this of course affects all performance parameters, some - like climb, accleration and manoeuvrability - are affected worse than others. Here is a comment on manoeuvrebility:

"The turning circle of this aircraft was larger than any of the other types engaged in combat. The high wing loading makes the plane mush in all maneuvers controlled by the elevators, and this also causes high speed stall in tight turns."

Looking at the battery installed in the P-47, thes are the armament parameters:

8x ,50 Browning M2 - 425 rpg, 33 s duration - 694 kg - 2,3 MW firepower - 74,2 MJ total energy

(Though two of the guns are labelled as "alternate", I think they were almost always carried. I also used the maximum ammunition capacity - no idea how this was handled operationally.)

An alternative battery with only slightly reduced firepower, but dramatically reduced weight could have been:

2x Hispano II - 350 rpg, 35 s duration - 272 kg - 2,1 MW firepower - firepower per weight: 7,8 kW/kg - 74,3 MJ total energy

The weight saving consists of 422 kg, or 930 lbs. Even for a 13800 lbs gross weight fighter like the P-47D, this is a massive difference.

And just for grins ... if the US had license-produced the Japanese Type 99-1 cannon, the battery might have been:

4x 20mm Type 99-1 - 283 rpg, 35 s duration - 395 kg - 2,1 MW firepower - 74,3 MJ total energy

Still a weight saving of 299 kg or 659 lbs.

(Note that Eglin did indeed suggest to change the armament, but as they proposed the "fast-firing" 12.7 mm machine gun which I guess became only ready after WW2 as the Browning M3, their suggestion obviously could not be followed.)

Regards,

Henning (HoHun)

 

[Clay_Allison]

Interesting!

A further question for you sir, since you are more knowledgeable about firearms then I- what made the M2 Browning so heavy? It has been my general impression that increasing rate of fire requires a lighter bolt assembly- but that, in turn, reduces the amount of power the gun can safely handle, and thus, cartridge power and muzzle velocity. Could there have been a way to lighten the M2 Browning, or increase ROF, without sacrificing its flat trajectory?

Among other things, it's a rectangle. Look at the Soviet Berezin UB and you can see that the M2 is just not an ideal shape for weight savings.

 

[Demetrious]

Among other things, it's a rectangle. Look at the Soviet Berezin UB and you can see that the M2 is just not an ideal shape for weight savings.

Now that I see it, it's quite evident.

The M2 Browning was conceived as an infantry and vehicle ground weapon, where it's hefty weight was an asset in controlling the tremendous recoil and thus improving accuracy. (The shmucks tasked to carry it around might have other views, of course. ) As far as I know, the only step taken to save weight in the aircraft models was to install a much lighter barrel that relied on the few-hundred MPH airstream to cool it.

 

[renrich]

Out of context here but saw on Military Channel that a Canadian sniper, in Afghanistan, I think, made a kill at a little over 2000 yards with a 50 BMG rifle.

 

[davparlr]

It is a question of procurement planning because if the planners had made a timely decision, the production change-over could have taken place early enough to put the 20 mm cannon in production in 1941. That's what the British accomplished.

I don't think there was enough data available in the late 30s, when the F4F was developed, indicating the lack of effectively of the 50 cal. I am not even sure there was data in 1941 that the 50 cals battery was a "failure". I do not think this info exist today.

Of course the US had a technical problem as well as a procurement problem, but both of these problems were home-made as on the other side of the pond, the Hispano was mass-produced and successfully made in combat.

Again, these problems would still need to be fixed.

Due to mistakes made earlier ... and the same applies to possible installation problems in F4F, F6F and F4U. Supermarine came up with a "universal wing" Spitfire that would accept 12.7 mm Browning and Hispano cannon within the same structure - I'm sure the Grumman and Vought could have come up with something similar.

I doubt if this would have changed the decision to stick with the 50s, just make the installation impact a bit easier if it was implemented. Some, maybe all, Mark IA Mustangs were delivered with 20s but there was never an upgrade to the Mark III or IV to incorporate 20s.

If you're lucky, you can get away with a failure, and Admiral King obviously thought that was what had happened at Midway. However, this doesn't make it any less a failure.

You're saying that the US, United Kingdom, Canada, all other countries that used aircraft with 50 cals, got away with failure for four years?

Here's a quote from Nimitz from Dean's "America's Hundred Thousand",

"Our F4F is markedly inferior to the Jap Zero in speed, maneuverability, and climb. These characteristics must be improved, but not at the cost of reducing the overall superiority that, in the Battle of Midway, enabled our carrier fighters to shoot down about three Zero fighters for each of our own lost. However much of this superiority may exist in our splendid pilots, part at least rest in the armor, armament, and leakproof tanks in our planes."

With comments like this from the war fighter, especially one of the outstanding Admirals of the war, it is easy to see why there was not much motivation to impact production for a modification to armament that had such rave reviews.

In reality, 20mm would probably not add much to the combat performance of the F4F. It would still be, as Nimitz stated, an inferior weapon.

Small countries like Denmark and Switzerland were producing their own aircraft cannon, and even a country with such a narrow industrial base as Japan had an operational cannon fighter ready for the Battle of Midway ... obviously, the Imperial Navy's procurement was doing a better job than the US Navy's.

By 1939, the US had pretty well settled on the 50 cals as being the primary fighter armament. The P-35, P-36, P-38, P-39, P-40, F2A, and F4F all had 50 cals as part of their armament although most also had secondary armament. The newly developed F4U also had 50 cals. By the time Britain changed to 20 mms, the 50 was well established in US aircraft production. There was no indication that these guns were not effective, which they were. And I suspect there were no statistics that supported the increased kill effectively of the 20 mm over the expected target, which you have never addressed. I am sure they accepted the fact that the 20s had more kill effectively over the 303s, but probably had little comparison to the 50s.

As the British switched to 20 mm cannon after careful consideration of all the options available to them, skipping the 12.7 mm machine gun rather quickly, and had already collected quite a bit of combat experience with them

What fighters were the British flying that used the 50 cals, other than limited number of F4Fs, and P-40s with only one 50 cal.?)

, the US military could simply have learned from the British example.

There certainly was not a shortage of examples of US not learning from the British, especially in regards to anti-sub warfare, but use of the 20 mm was not one of these.

There certainly was a lack of appreciation of the strengths of cannon in the US military, and not because these strengths were not evident at the time - all other major combattants employed cannon armament as a matter of fact.

There certainly was an appreciation for the fact that the considerable impact to production and logistics of adopting the 20 mm was not offset by any additional efficiencies it might provided, even in 1944, after considerable analysis.

Do you mean "clear stoppages in flight"?

Yes, inflight.

Nonsense - the RAF shot down hundreds of aircraft with 7.7 mm machine guns during the Battle of Britain, and yet there's no denying that they would have been better off with more powerful weaponry. It's the same with the 12.7 mm machine gun.

Certainly, the 20 mm was more effective than 50s against the bombers they were fighting, no so much against fighters.

Don't fool yourself - Tony' approach underestimates mine shells, but German war experience has shown that mine shells are considerably more effective against fighters than standard high-explosive (or armour-piercing) shells.

I am not fooling myself. I have no argument that the 20mm was not better, I am only saying that the decision to maintain 50s as the mainstream US fighter weapon was not a "failure" but rather a decision based on effectiveness, logistics and productivity.

Though Mike's ww2aircraftperformance is mostly focussed on performance, it also has some tactical trials strewn between.

This quote is from the Mustang III Tactical Trials:

"The fire-power consists of four .5 Browning's in the wings. This is very little compared with the Spitfire."

(In terms of total muzzle power, the Mustang III armament yields 1.14 MW firepower, while the Spitfire armament of two cannon and two 12.7 mm machine guns yields 2.69 MW firepower, confirming the laconic British statement.)

Interesting, there was no comment about the ineffectively of the four 50s, no recommendation to use 20mms, no effort to modify the Mark III with 20mm, even though the Mark IAs did come with 20mm, so installation must not have been a problem. I guess the British thought the 20mm update was not worth the effort for their 30-35 squadrons of Mark IIIs or the Mark IVs.

It is also interesting that, with all the experience with 20mms, the British also did not update their F4Fs or F6Fs with 20s. Updating these aircraft would probably not be any more difficult than updating the F4U, which the Navy did with the -1A. Again, they must have thought the advantage did not offset the effort, as the US had decided. This appears to be a rather cold decision, considering that the 50 cal was such a "failure" and "serious mistake", and the British would have known it!

(Note that Eglin did indeed suggest to change the armament, but as they proposed the "fast-firing" 12.7 mm machine gun which I guess became only ready after WW2 as the Browning M3, their suggestion obviously could not be followed.)

I am sure the decision not to update to the 20mm in 1943 was the same as it was in late 1944, i.e., improvement is not worth disturbing the production line and logistics (like the British on the Mark III and IV Mustang, F4F and F6F?), and to max probability of strikes for average pilots.

and if you read Admiral King's telegram, you'll realize that the Navy believed that insufficient armament (and poor fighter performance) almost made them lose the Battle of Midway.

I think your interpretation of Admiral Kings telegram. I don't think he was implying that the Battle of Midway was almost lost because of the performance of the F4F. I do not believe the battle was almost lost due to fighters with machine guns. I do not believe the F4F participated very much in the victory. They certainly were not there when the torpedo planes were destroyed and I do not believe they participated much when the dive bombers located and destroyed the Japanese carriers. I think the battle would have been won even if the Navy had use F2As with 30 cal MGs. Conversely, if the Navy had F4Fs with 20mms, they may saved the Lex, but not likely. So I think the impact of having 50s on the victory at Midway, one way or another, was minimal. King was concerned that the poor performance of the F4F could affect future battles, which it turns out, was wrong. As noted in Nimitz's message, he did not want to change the armament and felt it was a big contributor to what success the F4F had.

 

[davparlr]

Let me reiterate my position.

I have no argument that a mature 20mm design is more effective and would possibly help performance due to less weight. Probability of strikes would be reduced and sortie per kill is unknown (I don't know how much the gun would help). Probability comparisons of kill, given strike, is poorly known. Calculations have many variables, aspect, maneuver, etc.

I believe, and probably the war planners of the time believed, that, if the 20mms were adopted, there would have been a significant production delay and logistic trail at a time when quantity was vital.

There was no demand from the war fighter for improvements in firepower. No program manager was going to slow down production to incorporate a weapons improvement when the demand from the war fighter was for more aircraft with 50 cals, not delayed delivery due to updated guns.

The 50 cals were one cog on the immense war fighting machine known as US production. The US philosophy of providing vast quantities of capable, but maybe not perfect, war material was the true victors of the war.

If the 50 cal was a failure or mistake, it has to be the most successful failure in the history of warfare.

 

[renrich]

In reading Lundstrom's books and others also, I have not seen one remark made by USN pilots about the 50 BMG being deficient in terms of firepower whether against flyingboats, bombers or fighters or small craft up to and including DDs. On the contrary. Plenty of gripes about poor performance of the F4F4, plenty of gripes about reduced ammo supply being carried, plenty of gripes about faulty fuel gauges or bad fuel tanks or short range. But lots of kudos about the effectiveness of the 50 BMG. I would like to read King's telegram. Is it here online?

 

[HoHun]

Hi Davparlr,

>>>>>3) Production line incorporated the 50 cal, implementing the 20 mm would interrupt the line.

...

>I don't think there was enough data available in the late 30s, when the F4F was developed, indicating the lack of effectively of the 50 cal.

Look at your original point: You claimed that the 20 mm could only be introduced by interrupting the 12.7 mm production line.

Obviously, if the decision to introduce cannon had been made early enough, this would not have created any gap in aircraft armement supply.

Why this decision was not made in time is a different question - all other major powers made the decision, and most even made it in time. All of them made it in time for the Battle of Midway.

>Again, these problems would still need to be fixed.

You don't need to argue that the lead time was insufficient - for any lead time, there is a time at which a decision for cannon could have been made that would have introduced them just in time. That's the decision at which the US failed.

>You're saying that the US, United Kingdom, Canada, all other countries that used aircraft with 50 cals, got away with failure for four years?

Since I try not to oversimplify things, here is what the data I already posted tells you:

8x ,50 Browning M2 - 425 rpg, 33 s duration - 694 kg - 2,3 MW firepower - 74,2 MJ total energy
2x Hispano II - 350 rpg, 35 s duration - 272 kg - 2,1 MW firepower - firepower per weight: 7,8 kW/kg - 74,3 MJ total energy

The weight saving consists of 422 kg, or 930 lbs. Even for a 13800 lbs gross weight fighter like the P-47D, this is a massive difference.

The conclusions of the US experts on the P-47:

"b. The rate of climb is not as good as desired, which fact limits its suitability as a medium altitude fighter and as an interceptor.
c. All weight in the structure and accessories not vital to operational use should be eliminated."

So, the USAAF's failure to have cannon ready for the P-47 incurred a weight penalty of 930 lbs in the P-47, limiting the types' suitability as a fighter and reducing overall performance, manoeuvrability, range and payload.

This deterioration of technical and tactical parameters is something that every aircraft equipped with 12.7 mm Browning Machine guns suffered from, and it could have been avoided by the adoption of superior armement.

>In reality, 20mm would probably not add much to the combat performance of the F4F. It would still be, as Nimitz stated, an inferior weapon.

What Nimitz demanded was an improvement in performance without sacrificing the strengths of the F4F.

6x ,50 Browning M2 - 240 rpg, 18 s duration - 332 kg - 1,7 MW firepower
2x Hispano II - 180 rpg, 18 s duration - 189 kg - 2,1 MW firepower

According to my calculations, this would have improved the performance of the F4F-4 by:

- 2 km/h in top speed
- 2:30 min reduction in climb time to 8 km
- A 5 % increase in turn rate at sea level, and an 8 % increase at 8 km.

Operationally, the reduction in time to altitude probably is the most important improvement.

As pointed out in my previous posts, increasing the ammunition load would also have been possible, adressing the complaint Admiral King made - and this was a specific complaint about a weakness of the F4F's armament.

>By 1939, the US had pretty well settled on the 50 cals as being the primary fighter armament.

Again the lead time question ...

>And I suspect there were no statistics that supported the increased kill effectively of the 20 mm over the expected target, which you have never addressed.

Historical statistics: In 1939, there were obviously none. However, as I pointed out above, all other major powers had even before decided to go for cannon, obviously considering the material available at the time to be sufficient.

Modern statistics: There is enough data in this thread that I consider the topic extremely well-addressed. Any specific question you might have, just ask.

>What fighters were the British flying that used the 50 cals, other than limited number of F4Fs, and P-40s with only one 50 cal.?)

Hm, looks like a misunderstanding of my regrettably ambiguous sentence: "As the British switched to 20 mm cannon after careful consideration of all the options available to them, skipping the 12.7 mm machine gun rather quickly, and had already collected quite a bit of combat experience with them, the US military could simply have learned from the British example."

My clarification: The British had considered and rejected the 12.7 mm machine gun in favour of the cannon as primary fighter armament, and collected combat experience *with the 20 mm cannon*, which is what the US could have learned something from.

>Interesting, there was no comment about the ineffectively of the four 50s, no recommendation to use 20mms, no effort to modify the Mark III with 20mm, even though the Mark IAs did come with 20mm, so installation must not have been a problem. I guess the British thought the 20mm update was not worth the effort for their 30-35 squadrons of Mark IIIs or the Mark IVs.

The pressure towards standardization in fact grew during the war and probably would have made it impossible for the British in 1944 to get it their way. If only one standard version of the P-51D/K was going to be produced, it would obviously be armed to American standards. The situation for the Mark IA had been different, and the wing actually had been re-designed between the Mark IA and the P-51D.

>Interesting, there was no comment about the ineffectively of the four 50s

The quote:

"The fire-power consists of four .5 Browning's in the wings. This is very little compared with the Spitfire."

I read this as "very little fire-power compared with the Spitfire", and little firepower equates poor effectiveness.

What do you read this as?

>Certainly, the 20 mm was more effective than 50s against the bombers they were fighting, no so much against fighters.

Hm, correct me if I'm wrong, but this looks like a completely unsupported claim to me. In fact, the Luftwaffe data I quoted indicates the opposite - explosive shells are even more effective against fighters than against bombers.

>I am only saying that the decision to maintain 50s as the mainstream US fighter weapon was not a "failure" but rather a decision based on effectiveness, logistics and productivity.

It was a decision that resulted in inferior firepower, performance, range and maneovurability of tens of thousands of US-built fighters, directly contributing to the fate of the thousands of Allied pilots that were killed flying these fighters.

>I think your interpretation of Admiral Kings telegram.

Hm ...

>I don't think he was implying that the Battle of Midway was almost lost because of the performance of the F4F.

What I wrote:

"Admiral King's telegram shows intense concern about the quality of the entire weapons system. King's specific demands were:

- Reduce the weight of the F4F-4.
- Increase the ammunition supply.

The Hispano II example battery addresses both issues King raises with the F4F-4 and its armament by increasing the ammunition supply by 40% and saving about 324 lbs of weight at the same time. It also increases firepower."

>As noted in Nimitz's message, he did not want to change the armament and felt it was a big contributor to what success the F4F had.

Nimitz did not say he did not want to change the armament, but that he did not want to sacrifice the "the overall superiority", only "part at least rest in the armor, armament, and leakproof tanks". He was wise enough not to try to micro-manage the improvement, but only pointed out that performance should not be improved by stripping the aircraft of components that had proved their worth in combat. A cannon-armed Wildcat with improved firepower at improved performance would have met his demand nicely.

>Probability of strikes would be reduced and sortie per kill is unknown (I don't know how much the gun would help). Probability comparisons of kill, given strike, is poorly known. Calculations have many variables, aspect, maneuver, etc.

The problem is not half as complex as you seem to think. The firepower, measured in MW, is an excellent indicator of the effectiveness of the weapon, judging by the various historical accounts presented here and elsewhere, British and Soviet data both show that the vast majority of kills were scored at very short ranges where the influence of other factors is minimal, contemporary doctrine (confirmed by Soviet data) shows that the rear aspect was the most effective shooting position, the German Schießfibel points out that a large pattern is not helpful in air combat and does not compensate for errors in lead estimation, and the "probability of strikes" is completely secondary to the "probability of kill" - which is improved by switching to cannon.

>I believe, and probably the war planners of the time believed, that, if the 20mms were adopted, there would have been a significant production delay and logistic trail at a time when quantity was vital.

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.

>If the 50 cal was a failure or mistake, it has to be the most successful failure in the history of warfare.

Hm, I have pointed out the substantial shortcomings of the 12.7 mm Browning in fine detail, so it's really not necessary to gloss them over with a broad generalization. I think we could be making quicker progress without such statements ... your factual points are appreciated, but I feel there is occasionally a bit of unnecessary "ballast" in your posts

Regards,

Henning (HoHun)

 

[billswagger]

I heard that .50 cal was more common with US planes until late in the war because a lot of the early model 20mm cannons would have a tendency to jam during a high G maneuver. The .50 cals were the tried and true, and offered other advantages for air to air combat, as far as accuracy and muzzle velocity. The 8 x.50 cals used on 47s equated to 100+ rounds per second when all eight guns were firing..
I'm not sure what the percentages are for hit/miss ratios. But it was clear that at the proper convergence, rounds at that rate of fire landing with in the same 10" radius, did the job as well as cannons might have.

Cannons did the same thing to airplanes, it just took less of them. You wouldn't need 8x 20mm, and even 4 x 20mm was more than adequate for air to air combat.

I guess my point is that, the armaments were designed to get the most out of the ammo. Probably requiring similar site time on target.
Was the 20mm a better munition?? side by side, I'd say yes.
but .50 cals coming out of 6 or 8 barrels would've been just as good for air to air capabilities.
Just get on Youtube, and type P-47 in the search. you'll get several visual examples of the 8 50s going to work. You can really see how the 8 .50s blanketed an area when the ground spits up dirt and debris behind the intended targets. It really is an awesome site.


View: https://www.youtube.com/watch?v=5SBQbbrGmaQ

 

[HoHun]

Hi Bill,

>I'm not sure what the percentages are for hit/miss ratios. But it was clear that at the proper convergence, rounds at that rate of fire landing with in the same 10" radius, did the job as well as cannons might have.

Good point. The question is just, "At what price"? And if the answer is "At 930 lbs extra weight over a comparable cannon battery", that should trigger some thought process ...

Regards,

Henning (HoHun)

 

[billswagger]

true, weight was a big factor...but an even bigger factor was a bird with jammed cannon guns. lol
which was a common problem with the 20mm, initially. US chose to go with reliability, until the 20mm went through its "teething" process. Eventually all the quirks were worked out, and you start to see cannons on late war US fighters.
When the P-47 came into action, it met all the specifications that the US demanded in a fighter, and for a short period in '43 it dominated the sky because it was the first fighter utilizing the turbocharger allowing high altitude for zoom dives,/ climbs.
I'd say its biggest disadvantage was the fuel load, and its climb rate in which several modifications to the propeller and engine helped improve immensely despite its weight. It was still a huge gas guzzler, and the need for a lighter more efficient plane was evident. hello P-51s..and they chose to arm it with 50s.
I think we can round and round, on this topic.
Lets not forget the .50 cal was more accurate at longer ranges and was preferred for air to air combat, while the 20mm did more damage it required a closer shot for better accuracy. It would've been ideal for larger targets, such as bombers or stationary ground targets and tanks.
I can think another tactical reason for using .50 cal:
saved time.....ammunition was already manufactured, supplied and stocked.
It was the tried and true munition of the last half decade, prior to the 20mm.

round and round we go...

 

[Glider]

Let me reiterate my position.


I believe, and probably the war planners of the time believed, that, if the 20mms were adopted, there would have been a significant production delay and logistic trail at a time when quantity was vital.

If I may make an observation here. The USA had four armouries producing many thousands of 20mm cannons that were never fitted to aircraft or obviously used in combat because of their unreliability. They simply went into store and were scrapped after the war. The same applied to the ammunition for the US M1/M2 20mm cannon.
As a result to amend these factories to make the US 20mm reliable may well have had an impact because fewer would have been built, but would have had no impact on the war as so many of the weapons were not used anyway.

It wouldn't have done any harm to change one armoury at a time to an amended design.

 

[HoHun]

Hi Bill,

>I'd say its biggest disadvantage was the fuel load, and its climb rate in which several modifications to the propeller and engine helped improve immensely despite its weight.

Oh, improvements can be combined - better propeller, better engine and lower weight are better than any two of the three alone.

And replacing 930 lbs of excess weight with 930 lbs of fuel would have certainly helped the P-47's fuel load

(On a more serious note, if you have seen the Breguet range equation, it's centered on the relation of loaded to empty weight, which of course improves by eliminating dead weight.)

>Lets not forget the .50 cal was more accurate at longer ranges

Have you checked the ranges at which kills were really scored in WW2? It's all up there in this thread ...

(I don't actually think there was a worthwhile difference in trajectories between the 12.7 mm Browning and the 20 mm Hispano II, by the way.)

Regards,

Henning (HoHun)