Armor Penetration - 20mm vs. .50 cal.
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Hi Billswagger,
>I don't claim to be an expert on the topic, but if the .50 cal weren't efficient enough then why were most p-47s and p-51s armed with them.
Lack of an alternative, and slow institutional learning on part of the USAAF.
>As for air to air combat...there weren't many fighters that could withstand .50 cal., especially eight or six of them. 20mm/30mm were more useful at hitting bombers and armored ground targets, but its use in the dogfight arena was discouraged if you had another armament to use.
Nonsense. Cannon were superior against any kind of air target, including fighters, and that cannon were developed as anti-bomber weapons is an old myth without any basis in facts.
Regards,
Henning (HoHun)
>I don't claim to be an expert on the topic, but if the .50 cal weren't efficient enough then why were most p-47s and p-51s armed with them.
Lack of an alternative, and slow institutional learning on part of the USAAF.
>As for air to air combat...there weren't many fighters that could withstand .50 cal., especially eight or six of them. 20mm/30mm were more useful at hitting bombers and armored ground targets, but its use in the dogfight arena was discouraged if you had another armament to use.
Nonsense. Cannon were superior against any kind of air target, including fighters, and that cannon were developed as anti-bomber weapons is an old myth without any basis in facts.
Regards,
Henning (HoHun)
Hi Elvis,
>The reason the larger caliber guns weren't used as often during WWII was that their rate of fire, and their performance, was relatively low in those days.
Quite the opposite ... cannon generally outperformed machine guns in WW2. Here is a firepower comparison by total (kinetical plus chemical) muzzle power for batteries selected to match the 8 x 12.7 mm Brownings of the P-47:
1x MK 108 - 104 rpg - 121 kg - 236% firepower - firepower per weight: 1036%
1x MK 103 - 120 rpg - 251 kg - 124% firepower - firepower per weight: 262%
2x MG 151/20 (MX) - 205 rpg - 172 kg - 124% firepower - firepower per weight: 383%
2x Hispano V - 233 rpg - 199 kg - 109% firepower - firepower per weight: 291%
2x MG 151/20 - 251 rpg - 191 kg - 93% firepower - firepower per weight: 259%
3x MG-FF/M - 164 rpg - 250 kg - 116% firepower - firepower per weight: 246%
2x Hispano II - 226 rpg - 211 kg - 94% firepower - firepower per weight: 237%
3x 37mm M4 - 44 rpg - 408 kg - 120% firepower - firepower per weight: 156%
6x MG 151 - 210 rpg - 482 kg - 111% firepower - firepower per weight: 122%
11x MG 131 - 311 rpg - 454 kg - 104% firepower - firepower per weight: 122%
8x ,50 Browning M2 - 275 rpg - 531 kg - 100% firepower - firepower per weight: 100%
27x MG 17 - 331 rpg - 585 kg - 107% firepower - firepower per weight: 97%
32x Browning ,303 - 401 rpg - 706 kg - 106% firepower - firepower per weight: 80%
>With the advent (or rather, return) of multi-barrelled, fast firing weapons, projectile size and performance grew very quickly.
It was only the US aircraft industry that adopted Gatling cannon as a standard - most other nations used single-barrel cannon, often based on the WW2 MK 213C. The multi-barrelled 20 mm cannon was in fact firing a smaller projectile than the 30 mm cannon dominating the field outside the US.
>Now the rate of fire could match, or even surpass, the smaller caliber guns that had been in use, while utilizing what had become, a more effective round.
Rate of fire is just one parameter, there are others (such as the destructiveness of each round) that are equally important. Focus on just one parameter can lead to erroneous conclusions ...
Regards,
Henning (HoHun)
>The reason the larger caliber guns weren't used as often during WWII was that their rate of fire, and their performance, was relatively low in those days.
Quite the opposite ... cannon generally outperformed machine guns in WW2. Here is a firepower comparison by total (kinetical plus chemical) muzzle power for batteries selected to match the 8 x 12.7 mm Brownings of the P-47:
1x MK 108 - 104 rpg - 121 kg - 236% firepower - firepower per weight: 1036%
1x MK 103 - 120 rpg - 251 kg - 124% firepower - firepower per weight: 262%
2x MG 151/20 (MX) - 205 rpg - 172 kg - 124% firepower - firepower per weight: 383%
2x Hispano V - 233 rpg - 199 kg - 109% firepower - firepower per weight: 291%
2x MG 151/20 - 251 rpg - 191 kg - 93% firepower - firepower per weight: 259%
3x MG-FF/M - 164 rpg - 250 kg - 116% firepower - firepower per weight: 246%
2x Hispano II - 226 rpg - 211 kg - 94% firepower - firepower per weight: 237%
3x 37mm M4 - 44 rpg - 408 kg - 120% firepower - firepower per weight: 156%
6x MG 151 - 210 rpg - 482 kg - 111% firepower - firepower per weight: 122%
11x MG 131 - 311 rpg - 454 kg - 104% firepower - firepower per weight: 122%
8x ,50 Browning M2 - 275 rpg - 531 kg - 100% firepower - firepower per weight: 100%
27x MG 17 - 331 rpg - 585 kg - 107% firepower - firepower per weight: 97%
32x Browning ,303 - 401 rpg - 706 kg - 106% firepower - firepower per weight: 80%
>With the advent (or rather, return) of multi-barrelled, fast firing weapons, projectile size and performance grew very quickly.
It was only the US aircraft industry that adopted Gatling cannon as a standard - most other nations used single-barrel cannon, often based on the WW2 MK 213C. The multi-barrelled 20 mm cannon was in fact firing a smaller projectile than the 30 mm cannon dominating the field outside the US.
>Now the rate of fire could match, or even surpass, the smaller caliber guns that had been in use, while utilizing what had become, a more effective round.
Rate of fire is just one parameter, there are others (such as the destructiveness of each round) that are equally important. Focus on just one parameter can lead to erroneous conclusions ...
Regards,
Henning (HoHun)
Other members replied the air-to-air part, so I'd try to cover the air-to-tank part.
Most of the 20mm aircraft cannons were only as good as the .50 for piercing the armor, at least MG 151/20 and ShVAK. Hispano II was slightly better though, but hardly able to pierce even Pz-III armor.
Fuel carts pulled by tanks in WWII are a new thing to me, please add some info to back that up
As for the damage done by bullets richocheting from ground piercing the 10-15mm of steel, it's to far-fetched to me.
drgondog
Major
Yes - the 'form' is aerodynamic shape (ogive, etc) which the 3-D profile of the projectile.
The Ballistic coefficient will be derived from the shape, whereas the sectional density can be the same for many different shapes as long as the diameter and mass are the same.
Colin1
Senior Master Sergeant
An established tactic for P-47s engaging armoured ground targets
Elvis
Chief Master Sergeant
While I appreciate the above comments and with all due respect to your knowledge and the fact that you take great pains to help keep the record "straight" here, I think this is a case of letting Soren speak for himself.
My apologies if that comes across rudely. Its not meant to, its just that I was replying to a comment that Soren made and was just trying to get a clearer picture of what he was actually saying.
Elvis
Elvis
Chief Master Sergeant
Forgive my lack of clarity, I wasn't saying that cannons fitted to aircraft were inferior to machine guns, as far as the cartridge's performance was concerned.
The Britsh proved that a large, slow moving projectile is actually better at stopping an adversary, compared to a lighter, faster moving projectile during some testing that was performed in the early 1900's.
However, that testing did not include trying to hit a moving target, either.
I have read reports that WWII pilots preferred large caliber machine guns (I assume they're referring to 50 cal.) compared to cannons because it was easier to put more shots on the target and the machine guns tended to "jar" those planes less (making aiming easier, once the guns started firing).
Thus I was defining "low performance" as a combination of a slower rate of fire and the inability to stay on target, once the guns started firing.
As for my comments concerning multi-barrelled, rapid fire cannons was concerned, yes, I was speaking from the US point of view.
Except for the 20mm guns used in the F-86 (which I understand actually worked more like a revolver), I think all guns used on US aircraft since the time of Korea have been multi-barrelled weapons.
Elvis
Hi Elvis,
>Forgive my lack of clarity, I wasn't saying that cannons fitted to aircraft were inferior to machine guns, as far as the cartridge's performance was concerned.
Oh, I'm afraid my post was deficient in clarity as well. I wasn't really concerned merely with the performacne of the cartridge, but actually meant to point out that cannon were decidedly superior to machine guns if you compare entire weapons systems.
That's what the numbers in my table show - you get the same firepower from cannon at a much lower weight penalty than you get from machine guns, or for a battery of identical weight, you get much superior firepower from cannon.
>The Britsh proved that a large, slow moving projectile is actually better at stopping an adversary, compared to a lighter, faster moving projectile during some testing that was performed in the early 1900's.
If we're talking about WW2 air-to-air gunnery, there is not the sharp contrast noted in this "old" example. The 12.7 mm API projectile had a muzzle velocity of 890 m/s, the 20 mm Hispano II HE shell 860 m/s, and the MG 151/20 mine shell 805 m/s - that's about a 10 % span.
There also were cannon that were designed for lower muzzle velocities, but this was due to a deliberate design decision, not due to some inherent characteristic inevitable for cannon as your post implies.
>I have read reports that WWII pilots preferred large caliber machine guns (I assume they're referring to 50 cal.) compared to cannons because it was easier to put more shots on the target and the machine guns tended to "jar" those planes less (making aiming easier, once the guns started firing).
Hm, what can I say - sounds like utter nonsense I doubt someone would prepare a "report" on pilot's preferences, and if even he did, few pilots would have had an opportunity to actually compare the effect of heavy machine guns to that of cannon in combat, making it impossible to come up with a valid conclusion. It's fairly evident that any WW2 air force that actually had a choice went from machine gun to cannon, and I'm not aware of any one that ever made the opposite switch. Post-war popular book talk rationalizing the USAAF's failure to employ cannon, if you ask me.
>Thus I was defining "low performance" as a combination of a slower rate of fire and the ability to stay on target, once the guns started firing.
The pattern size of the 12.7 mm Browning, especially in the wing-mounted installations typical for USAAF fighters, was considerably larger than that of Luftwaffe cannon, which were very accurate in comparison. And if someone told you that cannon recoil would bounce about the nose of a fighter enough to spoil the pilot's aim, he was feeding you sea stories
>Except for the 20mm guns used in the F-86 (which I understand actually worked more like a revolver), I think all guns used on US aircraft since the time of Korea have been multi-barrelled weapons.
Sounds about right. However, this is not a worldwide design consensus, but in fact an exclusively US engineering tradition. Most Western nations prefer MG-213C-style revolver types of 27 to 30 mm, while the Russians have been very flexible in their cencept, coming up with a variety of different, but usually well-designed weapons of 23 mm to 37 mm over the decades. (The US actually considered switching to a 25 mm gun with the introduction of the F-15, and I think a similar plan was made for the F-22, but both came to nothing.)
Regards,
Henning (HoHun)
>Forgive my lack of clarity, I wasn't saying that cannons fitted to aircraft were inferior to machine guns, as far as the cartridge's performance was concerned.
Oh, I'm afraid my post was deficient in clarity as well. I wasn't really concerned merely with the performacne of the cartridge, but actually meant to point out that cannon were decidedly superior to machine guns if you compare entire weapons systems.
That's what the numbers in my table show - you get the same firepower from cannon at a much lower weight penalty than you get from machine guns, or for a battery of identical weight, you get much superior firepower from cannon.
>The Britsh proved that a large, slow moving projectile is actually better at stopping an adversary, compared to a lighter, faster moving projectile during some testing that was performed in the early 1900's.
If we're talking about WW2 air-to-air gunnery, there is not the sharp contrast noted in this "old" example. The 12.7 mm API projectile had a muzzle velocity of 890 m/s, the 20 mm Hispano II HE shell 860 m/s, and the MG 151/20 mine shell 805 m/s - that's about a 10 % span.
There also were cannon that were designed for lower muzzle velocities, but this was due to a deliberate design decision, not due to some inherent characteristic inevitable for cannon as your post implies.
>I have read reports that WWII pilots preferred large caliber machine guns (I assume they're referring to 50 cal.) compared to cannons because it was easier to put more shots on the target and the machine guns tended to "jar" those planes less (making aiming easier, once the guns started firing).
Hm, what can I say - sounds like utter nonsense
I doubt someone would prepare a "report" on pilot's preferences, and if even he did, few pilots would have had an opportunity to actually compare the effect of heavy machine guns to that of cannon in combat, making it impossible to come up with a valid conclusion. It's fairly evident that any WW2 air force that actually had a choice went from machine gun to cannon, and I'm not aware of any one that ever made the opposite switch. Post-war popular book talk rationalizing the USAAF's failure to employ cannon, if you ask me.>Thus I was defining "low performance" as a combination of a slower rate of fire and the ability to stay on target, once the guns started firing.
The pattern size of the 12.7 mm Browning, especially in the wing-mounted installations typical for USAAF fighters, was considerably larger than that of Luftwaffe cannon, which were very accurate in comparison. And if someone told you that cannon recoil would bounce about the nose of a fighter enough to spoil the pilot's aim, he was feeding you sea stories
>Except for the 20mm guns used in the F-86 (which I understand actually worked more like a revolver), I think all guns used on US aircraft since the time of Korea have been multi-barrelled weapons.
Sounds about right. However, this is not a worldwide design consensus, but in fact an exclusively US engineering tradition. Most Western nations prefer MG-213C-style revolver types of 27 to 30 mm, while the Russians have been very flexible in their cencept, coming up with a variety of different, but usually well-designed weapons of 23 mm to 37 mm over the decades. (The US actually considered switching to a 25 mm gun with the introduction of the F-15, and I think a similar plan was made for the F-22, but both came to nothing.)
Regards,
Henning (HoHun)
davparlr
Senior Master Sergeant
In addition to the F-86, several US aircraft post-Korea used non multi-barrel 20mm cannons, the F-100, F-101A, and the F-5 (all using the F-86 gun). In addition, the US Navy had several aircraft that used non multi-barrel cannons, including the F-8.
davparlr
Senior Master Sergeant
I don't think it was a failure to employ cannon, but rather a decision. I have not seen any complaints about the use of 50 cals by the crews of US military aircraft. This included the Joint Fighter Conference in 1944, where multi-service combat airmen were involve in this discussion. In fact, I have read where some pilots perferred the four gun F4F-3 over the six gun F4F-5 (due mainly to weight).
For the type of combat the US air services were involved in, the 50 cals were apparently sufficient.
Elvis
Chief Master Sergeant
You know, I didn't think about those planes when I posted those comments, but you're right.
None of them used a multi-barrelled gun.
I never knew that all used the same gun, however. That's interesting.
Thanks.
Elvis
Hi Davparlr,
>I don't think it was a failure to employ cannon, but rather a decision.
Of course it was a failure, considering that it gave them the same firepower and ammunition supply they could have had from two Hispano canon while saving more than 200 kg of weight.
>I have not seen any complaints about the use of 50 cals by the crews of US military aircraft.
As I already pointed out, they had no comparison. And I have not seen any comments that show that they were aware of the weight penalties they were paying for their overweight guns ... pilots certainly were critical of weight issues. The rear warning radar at first was rejected by the P-47 pilots in the ETO because they didn't believe it was worth its weight.
>In fact, I have read where some pilots perferred the four gun F4F-3 over the six gun F4F-5 (due mainly to weight).
Due to weight, and also due to duration of fire. However, if you look at the details, you'll find that it would have been possible to give the F4F-4 (guess your "-5" was only a type) a cannon battery that weighed no more than that of the F4F-3 while at the same time increasing firepower and duration of fire beyond that of either type ... simply by using cannon.
The 4x 12.7 mm battery had 1720 rounds of ammunition while the 6x 12.7 mm battery had only 1440 rounds. What the pilot bemoaned was that the new aircraft had less ammunition ...
4x ,50 Browning M2 - 430 rpg, 33 s duration - 305 kg - 1,1 MW firepower - 37.5 MJ total supply
6x ,50 Browning M2 - 240 rpg, 18 s duration - 332 kg - 1,7 MW firepower - 31.4 MJ total supply
Here is an alternative battery that would have done a much superior job:
2x Hispano II - 417 rpg, 42 s duration - 305 kg - 2,1 MW firepower - 88.5 MJ total supply
What would these cannon have done for the US navy?
- They would have increased firepower by a factor of almost 2 over the F4F-3 battery (at the same weight).
- They would have increased the total firing duration by a factor of 1.3 over the F4F-3 battery (at the same weight).
- They would have increased the total ammunition supply by a factor of 2.4 over the F4F-3 (at the same weight).
- It would have increased firepower by more than 20% over the six-gun battery of the F4F-4 (at lower weight).
So whatever way you look at it, the 12.7 mm Browning armament was inferior to contemporary cannon, and replacing it with a different type of gun would have had considerable performance and tactical benefits for the US forces.
>For the type of combat the US air services were involved in, the 50 cals were apparently sufficient.
You can excuse any type of inferior Allied equipment that way since it was still "sufficient to win the war". That really doesn't mean anything.
Regards,
Henning (HoHun)
>I don't think it was a failure to employ cannon, but rather a decision.
Of course it was a failure, considering that it gave them the same firepower and ammunition supply they could have had from two Hispano canon while saving more than 200 kg of weight.
>I have not seen any complaints about the use of 50 cals by the crews of US military aircraft.
As I already pointed out, they had no comparison. And I have not seen any comments that show that they were aware of the weight penalties they were paying for their overweight guns ... pilots certainly were critical of weight issues. The rear warning radar at first was rejected by the P-47 pilots in the ETO because they didn't believe it was worth its weight.
>In fact, I have read where some pilots perferred the four gun F4F-3 over the six gun F4F-5 (due mainly to weight).
Due to weight, and also due to duration of fire. However, if you look at the details, you'll find that it would have been possible to give the F4F-4 (guess your "-5" was only a type) a cannon battery that weighed no more than that of the F4F-3 while at the same time increasing firepower and duration of fire beyond that of either type ... simply by using cannon.
The 4x 12.7 mm battery had 1720 rounds of ammunition while the 6x 12.7 mm battery had only 1440 rounds. What the pilot bemoaned was that the new aircraft had less ammunition ...
4x ,50 Browning M2 - 430 rpg, 33 s duration - 305 kg - 1,1 MW firepower - 37.5 MJ total supply
6x ,50 Browning M2 - 240 rpg, 18 s duration - 332 kg - 1,7 MW firepower - 31.4 MJ total supply
Here is an alternative battery that would have done a much superior job:
2x Hispano II - 417 rpg, 42 s duration - 305 kg - 2,1 MW firepower - 88.5 MJ total supply
What would these cannon have done for the US navy?
- They would have increased firepower by a factor of almost 2 over the F4F-3 battery (at the same weight).
- They would have increased the total firing duration by a factor of 1.3 over the F4F-3 battery (at the same weight).
- They would have increased the total ammunition supply by a factor of 2.4 over the F4F-3 (at the same weight).
- It would have increased firepower by more than 20% over the six-gun battery of the F4F-4 (at lower weight).
So whatever way you look at it, the 12.7 mm Browning armament was inferior to contemporary cannon, and replacing it with a different type of gun would have had considerable performance and tactical benefits for the US forces.
>For the type of combat the US air services were involved in, the 50 cals were apparently sufficient.
You can excuse any type of inferior Allied equipment that way since it was still "sufficient to win the war". That really doesn't mean anything.
Regards,
Henning (HoHun)
Demetrious
Airman 1st Class
- 104
- Aug 22, 2007
Incorrect- as far as the F4F and the Pacific Theater are concerned, at the very least.
The prime advantage of .50 caliber guns over the Hispano is that they have a much higher rate of fire, greatly increasing one's chance to hit. Of course, this doesn't mean as much when one considers that a single 20mm strike is worth four or five .50 cal strikes (at least,) but in the Pacific Theater, this was entirely insignificant, since the principal opponent was the Zero. The Zero, as we all know, would vanish in an amusingly pyrotechnic fashion from even the briefest of .50 caliber bursts. This same vulnerability held true for most Japanese aircraft, and even their tanks. Given this, the increase in destructive firepower was of little value, and the trade-off in ease of connecting was horrible. Most pilots were not very good shots, after all, and given the difficulty of aerial gunnery, nobody can blame them.
Given this, I am at a loss to see why the reluctance of the USN to equip their F4F's with Hispano cannons is seen as a "failure."
There is a further consideration that speaks louder, however- production problems in obtaining Hispano cannons in the first place. Many cannons of the war had good destructive power but regrettable ballistics, making them close-range sledgehammers (early German, Russian, and Japanese 20mms are all guilty of this,) but the Hispano was a truly wonderful gun; one of the few cannons with ballistics that could approach that of the .50 cal. It's wonderfully flat trajectory went a long, long way towards forgiving the usual vice of cannons; slow rate of fire, and I have no doubt that the USAF and USN would have used many more Hispanos, if only they could. As it stood, however, production of the single 20mm Hispano for the P-38 gave them enough trouble.
Also, from Wikipedia:
The USN, at least, lusted for their cannons: they just couldn't get them. A failure of implementation, certainly- not a failure of policy.
Standard .50 ball ammo loses in a comparison with 20mm. The latter being an explosive clearly has advantages. The .50 API (armor piercing incendiary) was a more volatile round than the 20mm, though. It penetrated and then began to burn explosively at a much higher temperature and volatility than a 20mm. Plus, it could lodge itself into a spar and just sit there and burn violently. It was like a buzz saw. Regular incendiary begin burning in the barrel and quickly burned out the barrel. That's why they weren't used extensively. Many pilots preferred not to use them except as markers indicating they were low on ammo. They preferred API rounds because they didn't ruin the gun barrels and were much more effective than standard ball ammo. Also consider rate of fire and time-on-target. High rates of fire (900-1000 RPM) with the .50 outstripped any 20mm meaning those milliseconds the opponent was bracketed the .50 had the advantage of more rounds on-target.
My Pop was a P-47 and P-51 driver and he seldom used anything but ball and API. In contests he was part of with the 20mm equipped British planes of that period the American heavy MG equipped types typically left more damage than the British types pass-for-pass. The 20mm just didn't deliver the same weight of metal as the heavy MGs because the 20mm was slower firing. Add to that the .50 API round and the advantages clearly weighed in favor of the .50 BMG.
My Pop was a P-47 and P-51 driver and he seldom used anything but ball and API. In contests he was part of with the 20mm equipped British planes of that period the American heavy MG equipped types typically left more damage than the British types pass-for-pass. The 20mm just didn't deliver the same weight of metal as the heavy MGs because the 20mm was slower firing. Add to that the .50 API round and the advantages clearly weighed in favor of the .50 BMG.
I'll let to Henning to deal with rest (
), but could you please explain the quoted part, Sweb? What was burning in the barrell?I'll let to Henning to deal with rest (
Incendiary rounds - tracers - were ignited when the round was fired so it began burning inside the gun barrel. They were white-hot and caused damage to the rifling of the barrel. Also, because it burned it lost weight. Losing weight meant it traveled a flatter trajectory than standard ball (FMJ rounds). Incendiaries were used to give a gunner an "idea" where his rounds were going relative to a target. Knowing his tracers were lighter and took a flatter trajectory he would aim accordingly placing his tracers above the target. Experienced gunners got to know their ranges and round characteristics so they began to eliminate tracers, usually one in every ten rounds, from their belts. It was a common event when fighters returned with burned out barrels armorers had to replace when servicing the guns. Long bursts and/or high incendiary usage could quickly ruin the rifling inside the barrel causing subsequent rounds to have erratic trajectories or even tumble in what we shooters call "flyers". Armor piercing rounds (API) did not burn in the barrel. They burned after piercing the target and they burned a magnesium composition that went instantaneously to a white-hot temperature that - simply stated - melted everything in close proximity to it. Magnesium, once ignited, cannot be extinguished. It burns itself out. One round lodged in an opponents spar will damage it to the point of failure. Tracers, on the other hand, because they burn of their weight on the way to the target have no striking power. If they penetrate they can do some serious damage but they weren't designed to penetrate. In WWI where wood and fabric were the bulk of construction materials the tracer was deadly. By WWII it was more of a "marker" round for gunners.
Some pilots flew types that had individual gun selectors. The Corsair had 6 individual gun solenoid selector switches. The pilot could elect to use 4 in combat and save 2 for the trip home. This kind of option allowed them to stagger barrel wear and up their usage of mixed round compositions in their belts. The P-47 did not have such an option. One switch armed all 8 gun solenoids so they had to be a bit more conservative in their tracer usage and burst lengths lest they burn out their barrels early in an action.
Edit: I forgot to mention that tracers let the opponent know where their attacker was coming from. This gave them the chance to maneuver immediately rather than take the time to get a visual on their attacker.
Hi Demetrious,
>Given this, I am at a loss to see why the reluctance of the USN to equip their F4F's with Hispano cannons is seen as a "failure."
Since you tried to evade the question of destruciveness with a hand-waving argument, let me remind you of the math:
Pk_total = P_hit_round * n_rounds * Pk_round
As P_hit_round, the probability of a hit for a single round, is not likely to be any worse for the Hispano cannon than for the 12.7 mm Browning, the total probability for a kill for a given number of rounds Pk_total depends on n_rounds * Pk_round.
As this parameter is superior for cannon, the entire cannon battery is superior.
>It's wonderfully flat trajectory went a long, long way towards forgiving the usual vice of cannons; slow rate of fire
You're way removed from reality ... the vast majority of kills were scored at short ranges where the trajectory curvature did not matter at all. And at long ranges, the out-of-centre mounting introduced aiming problems for wing-mounted armament that was more serious than trajectory curvature anyway. Rate-of-fire fallacy, see above.
Here is some British data on combat ranges from RAF report "2nd T.A.F./O.R.S. Report No. 43" (which I unfortunately dont' know in its entirety), listing 482 combats as reviewed from RAF gun camera films from Spitfire and Tempest fighters.
Of the 272 "destroyed" claims resulting from these 482 combats, 86 % were from combat distances of 400 yards or less.
The table (1 - 2 % inaccuracy due to rounding in the original report):
600 yards and less: 96 %
400 yards and less: 86 %
300 yards and less: 74 %
200 yards and less: 52 %
The US experience was not much different ... you might have heard of Frederick C. Blesse, WW2 and Korean War veteran and author of the first "fighter pilot's bible", titled "No Guts, No Glory". His comments confirm the short firing ranges I pointed out:
"This business of firing at greater ranges is a popular misconception in regard to Korea. Contrary to much that has been published, the Fighter Pilots who shot down more than an occasional Mig or two, got them around 400-1200 feet just like they did in Europe and the Southwest Pacific during World War II."
> The Zero, as we all know, would vanish in an amusingly pyrotechnic fashion from even the briefest of .50 caliber bursts.
Here is a quote from a despatch from Admiral Nimitz to Admiral King sent on 20 June 1942 (Kudos to Amsel!:
"TAKE ANY POSSIBLE STEPS TO LIGHTEN F4F4 AND INCREASE AMMUNITION CAPACITY EVEN AT COST OF REDUCTION IN NUMBER OF GUNS"
Note that from switching to Hispano cannon, you get a 20% firepower increase coupled with a 27 kg weight reduction and an ammunition supply increase, both expressed in duration of fire and in total energy, by more than a factor of two.
4x ,50 Browning M2 - 430 rpg, 33 s duration - 305 kg - 1,1 MW firepower - 37.5 MJ total supply
6x ,50 Browning M2 - 240 rpg, 18 s duration - 332 kg - 1,7 MW firepower - 31.4 MJ total supply
2x Hispano II - 417 rpg, 42 s duration - 305 kg - 2,1 MW firepower - 88.5 MJ total supply
If the Hispano had been made ready in time, the Navy could have conveniently adjusted weight and ammunition supply between these two extremes ...
Maximum ammunition supply:
2x Hispano II - 472 rpg, 47 s duration - 332 kg - 2,1 MW firepower - firepower per weight: 6,4 kW/kg
Maximum weight savings:
2x Hispano II - 180 rpg, 18 s duration - 189 kg - 2,1 MW firepower - firepower per weight: 11,3 kW/kg
... while surpassing all relevant parameters of the existing machine gun batteries.
Of course it was a failure not to have this option when the Battle of Midway showed the shortcomings of the Browning-armed Wildcat. The worse failure however was not to have installed cannon in the Wildcats even before Midway.
Regards,
Henning (HoHun)
>Given this, I am at a loss to see why the reluctance of the USN to equip their F4F's with Hispano cannons is seen as a "failure."
Since you tried to evade the question of destruciveness with a hand-waving argument, let me remind you of the math:
Pk_total = P_hit_round * n_rounds * Pk_round
As P_hit_round, the probability of a hit for a single round, is not likely to be any worse for the Hispano cannon than for the 12.7 mm Browning, the total probability for a kill for a given number of rounds Pk_total depends on n_rounds * Pk_round.
As this parameter is superior for cannon, the entire cannon battery is superior.
>It's wonderfully flat trajectory went a long, long way towards forgiving the usual vice of cannons; slow rate of fire
You're way removed from reality ... the vast majority of kills were scored at short ranges where the trajectory curvature did not matter at all. And at long ranges, the out-of-centre mounting introduced aiming problems for wing-mounted armament that was more serious than trajectory curvature anyway. Rate-of-fire fallacy, see above.
Here is some British data on combat ranges from RAF report "2nd T.A.F./O.R.S. Report No. 43" (which I unfortunately dont' know in its entirety), listing 482 combats as reviewed from RAF gun camera films from Spitfire and Tempest fighters.
Of the 272 "destroyed" claims resulting from these 482 combats, 86 % were from combat distances of 400 yards or less.
The table (1 - 2 % inaccuracy due to rounding in the original report):
600 yards and less: 96 %
400 yards and less: 86 %
300 yards and less: 74 %
200 yards and less: 52 %
The US experience was not much different ... you might have heard of Frederick C. Blesse, WW2 and Korean War veteran and author of the first "fighter pilot's bible", titled "No Guts, No Glory". His comments confirm the short firing ranges I pointed out:
"This business of firing at greater ranges is a popular misconception in regard to Korea. Contrary to much that has been published, the Fighter Pilots who shot down more than an occasional Mig or two, got them around 400-1200 feet just like they did in Europe and the Southwest Pacific during World War II."
> The Zero, as we all know, would vanish in an amusingly pyrotechnic fashion from even the briefest of .50 caliber bursts.
Here is a quote from a despatch from Admiral Nimitz to Admiral King sent on 20 June 1942 (Kudos to Amsel!
:"TAKE ANY POSSIBLE STEPS TO LIGHTEN F4F4 AND INCREASE AMMUNITION CAPACITY EVEN AT COST OF REDUCTION IN NUMBER OF GUNS"
Note that from switching to Hispano cannon, you get a 20% firepower increase coupled with a 27 kg weight reduction and an ammunition supply increase, both expressed in duration of fire and in total energy, by more than a factor of two.
4x ,50 Browning M2 - 430 rpg, 33 s duration - 305 kg - 1,1 MW firepower - 37.5 MJ total supply
6x ,50 Browning M2 - 240 rpg, 18 s duration - 332 kg - 1,7 MW firepower - 31.4 MJ total supply
2x Hispano II - 417 rpg, 42 s duration - 305 kg - 2,1 MW firepower - 88.5 MJ total supply
If the Hispano had been made ready in time, the Navy could have conveniently adjusted weight and ammunition supply between these two extremes ...
Maximum ammunition supply:
2x Hispano II - 472 rpg, 47 s duration - 332 kg - 2,1 MW firepower - firepower per weight: 6,4 kW/kg
Maximum weight savings:
2x Hispano II - 180 rpg, 18 s duration - 189 kg - 2,1 MW firepower - firepower per weight: 11,3 kW/kg
... while surpassing all relevant parameters of the existing machine gun batteries.
Of course it was a failure not to have this option when the Battle of Midway showed the shortcomings of the Browning-armed Wildcat. The worse failure however was not to have installed cannon in the Wildcats even before Midway.
Regards,
Henning (HoHun)
Hi Sweb,
>The 20mm just didn't deliver the same weight of metal as the heavy MGs because the 20mm was slower firing.
Well, here is a comparison of raw firepower (in terms of firepower at the muzzle, international decimal separator):
Me 262: 20,1 MW
Fw 190A-8/R2: 13 MW
Ta 152H: 7,6 MW
Fw 190A-8: 5,5 MW
Me 109K-4: 5,5 MW
Beaufighter Mk 21: 5,3 MW
Tempest: 4,9 MW
Fw 190A-4: 4,3 MW
Typhoon: 4,2 MW
Spitfire IXE: 2,7 MW
Spitfire VC: 2,5 MW
P-47D: 2,3 MW
P-38: 2,2 MW
Me 109G-6: 1,8 MW
Me 109E-4: 1,7 MW
P-51D: 1,7 MW
Me 109G-2: 1,4 MW
P-51C: 1,1 MW
Hurricane IIA: 1,1 MW
Spitfire II: 0,7 MW
Me 109F-2: 0,6 MW
Me 109E-1: 0,3 MW
Rate-of-fire losses through synchronization are not included, but with an electrical system as used by the Luftwaffe should be around 5 % - 10 % depending on type of gun and current flight parameters.
(The MG 151/20 installed have been considered to be using standard ammunition, not the more powerful late-war MX ammunition.)
>Add to that the .50 API round and the advantages clearly weighed in favor of the .50 BMG.
Larger calibres made it possible to design more effective rounds of any given ammunition type, and naturally there were API rounds available for 20 mm cannon as well. The 12.7 x 99 mm API contained just 0.86 g of incendiary, the 20 x 82 mm API 3.6 g, the 30 x 184 mm Pz.Brgr. 9.0 g.
However, as the German combat results showed, the most effective type of ammunition were not API rounds but mine shells, and these relied on a large amount of explosive that could not be crammed into machine-gun calibre shells.
The German 20 x 82 mm mine shell contained 20 g of explosives, while the 30 x 90 mm mine shell contained 96 g of explosives. I'm not aware of any high-explosive aircraft rounds for the 12.7 mm, but the Italian 12.7 x 81 mm HE shell carried just 0.6 g, as in illustration of what might have been possible in the smaller calibre.
Regards,
Henning (HoHun)
>The 20mm just didn't deliver the same weight of metal as the heavy MGs because the 20mm was slower firing.
Well, here is a comparison of raw firepower (in terms of firepower at the muzzle, international decimal separator):
Me 262: 20,1 MW
Fw 190A-8/R2: 13 MW
Ta 152H: 7,6 MW
Fw 190A-8: 5,5 MW
Me 109K-4: 5,5 MW
Beaufighter Mk 21: 5,3 MW
Tempest: 4,9 MW
Fw 190A-4: 4,3 MW
Typhoon: 4,2 MW
Spitfire IXE: 2,7 MW
Spitfire VC: 2,5 MW
P-47D: 2,3 MW
P-38: 2,2 MW
Me 109G-6: 1,8 MW
Me 109E-4: 1,7 MW
P-51D: 1,7 MW
Me 109G-2: 1,4 MW
P-51C: 1,1 MW
Hurricane IIA: 1,1 MW
Spitfire II: 0,7 MW
Me 109F-2: 0,6 MW
Me 109E-1: 0,3 MW
Rate-of-fire losses through synchronization are not included, but with an electrical system as used by the Luftwaffe should be around 5 % - 10 % depending on type of gun and current flight parameters.
(The MG 151/20 installed have been considered to be using standard ammunition, not the more powerful late-war MX ammunition.)
>Add to that the .50 API round and the advantages clearly weighed in favor of the .50 BMG.
Larger calibres made it possible to design more effective rounds of any given ammunition type, and naturally there were API rounds available for 20 mm cannon as well. The 12.7 x 99 mm API contained just 0.86 g of incendiary, the 20 x 82 mm API 3.6 g, the 30 x 184 mm Pz.Brgr. 9.0 g.
However, as the German combat results showed, the most effective type of ammunition were not API rounds but mine shells, and these relied on a large amount of explosive that could not be crammed into machine-gun calibre shells.
The German 20 x 82 mm mine shell contained 20 g of explosives, while the 30 x 90 mm mine shell contained 96 g of explosives. I'm not aware of any high-explosive aircraft rounds for the 12.7 mm, but the Italian 12.7 x 81 mm HE shell carried just 0.6 g, as in illustration of what might have been possible in the smaller calibre.
Regards,
Henning (HoHun)
