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Dave
The comment that one 20mm was equal to 3 x 0.5 was a general statement applying to the weapon, not one 20mm hit was equal to 3 x 0.5 hits. My understanding would be that he additional chance of obtaining a hit would have been factored into the equation. To put it another way the additonal chance of a hit would be more than 3 to 1 in the F86 favour due to the larger number of projectiles fired but the impact of a 20mm hit would be significantly higher.
Not likely since the probability of a strike is a variable depending on many other variables such as distance and gun sight. Most likely the analysis was made against a fixed target at a specific range. Once the baseline ballistics is determined and the damage measured, the impact of the other variables can be easily calculated. It is possible that the test was run on AP rounds and not explosive rounds, but I certainly would be surprised if they decided on weapons selection without including this very important factor, and I think this would have been brought up if it was not. This was a very high powered meeting; one of the participants at the conference was a C. A. Lindbergh, representing United Aircraft.
Also, since probability of strike is function of accuracy, the effectivity of the gun is a variable, but not the round. As accuracy increases the 50 cal is landing more rounds per 20mm round so the effectivity of the 50 changes but the 20mm does not.
The Northrop armament engineer I mentioned earlier that was proposing a 50 cal Gatling for the F-5 stated that the penetrating power of the 50 was an advantage in combating jet aircraft.
My copy of the book is out of my reach at the moment so you could be right but my memory was that it was a general statement not a specific breakdown. I do agree that your probability of a hit was done on the variables you mention however using those calculations. However my posting 81 shows a very significant advantage to the 20mm which far outweighs the additional hits obtained by the 0.5 which has to rely on hitting a vulnerable part whereas the 20mm is almost certain to do damage wherever it hits.Not likely since the probability of a strike is a variable depending on many other variables such as distance and gun sight. Most likely the analysis was made against a fixed target at a specific range. Once the baseline ballistics is determined and the damage measured, the impact of the other variables can be easily calculated. It is possible that the test was run on AP rounds and not explosive rounds, but I certainly would be surprised if they decided on weapons selection without including this very important factor, and I think this would have been brought up if it was not. This was a very high powered meeting; one of the participants at the conference was a C. A. Lindbergh, representing United Aircraft.
I was trying to say that the despite the additional hits of the 6 x 0.5 something that I do not doubt, the additional KE impact of the 20mm coupled with its much higher explosive content, still resulted in a 3 to 1 advantage.I don't really understand the last sentence. The probabilities I generated was for a one second burst with varying probability of accuracy.
No doubt he believed what he said but history has proven him wrong. The US went to 20mm as Europe went to 30mm, now the newest guns are in the 25 - 27mm band no one, of any nation, has ever gone back to the 0.5.The Northrop armament engineer I mentioned earlier that was proposing a 50 cal Gatling for the F-5 stated that the penetrating power of the 50 was an advantage in combating jet aircraft.
Is this what was used in the P-38? Do we know how they performed in the P-38?Yes and no, some of decisions were incompetent. the story of the US 20mm Hispano is a long and sad one. Some ordnance officials refused to change earlier decisions on details like chamber length ( a difference of 1/16 of an inch) no matter how many demonstrations showed it was wrong until guns were stacked in warehouses by the 10s of thousands with no takers because of the resulting poor reliability. In that case the decision to stick with the .50 rather than try to use defective 20mm guns was the right one. Bur it wasn't a question of sticking with a gun that was "good", it was a question of sticking with the lesser of two evils. a gun of adequate power and reliability (many early .50 cal installations weren't that good but that was the installation and not the basic gun) vs a harder hitting but much lower reliability gun, and again the lower reliablilty was pretty much the ordnance depts own doing, British guns (with the shorter chamber) being much more reliable than the American ones.
I thought it was developed from (or at least inspired by) the FG42 and perhaps the MG42. Sounds like something got lost in translation.The M60 was a mixed bag, it did some things right and got some things wrong and what was wrong was stupid stuff that shouldn't have been. One thing was that on early versions it was possible to assemble the gun with the gas piston in backwards, gun would fire one shot and stop. Can be gotten around by training (somewhat) by why not make the gun a little more soldier proof to begin with? another thing was that the barrel, gas cylinder and bi-pod came as a one piece unit. Carrying a spare barrel meant carrying a spare bi-pod. Now the bi-pod did give the gunner (or his assistant) something to hang onto while changing the barrel but it also meant the gun flopped on the ground when the bi-pod was removed. An asbestos glove was part of the barrel changing gear (according to the book). one cold over look such things on a WW I or 1920s machine gun. On a 1950s machine gun it leaves you wondering where the guys who approved it it were hiding for the last 20 years. An other feature )(not) was that the replaceable barrel had a fixed front sight. Bren guns had movable front sight sights. two or more barrels could be zeroed to the same point of impact using the same rear sight settings and the barrels swapped in combat with little or no change in impact with no work by the gunner. The M-60 required the gunner to know (or record in a pocket notebook) the rear sight settings for each barrel and change the zero setting on the sight each time the barrel was changed. Again,not a good feature on a a 1950s gun. There are a few other details that were less than world class.
All in all if leaves one less than impressed with some of the personnel in the ordnance dept. others may have done a very good job on other projects but US Ordnance was certainly far from infallible at times.
Was the issue really one of "upgrading" the Sherman, or switching from a medium tank to a heavy tank. At the time, I thought US Army doctrine favored medium tanks, with anti-tank guns and tank destroyers meant to tackle enemy heavy tanks. So I suppose the Sherman did was it was designed to do, be a medium tank.While the M-4 was a world class tank in 1941 (initial design) and 1942 and while ordnance tried the decision makers screwed this one up. Depending on you opponent NOT to upgrade his tanks for several more years is NOT smart. The decision to upgrade the Sherman (even if they didn't go for the M-26) should have been made sooner. Much like the Russians upgraded in the T-34 in early 1944.
Is this what was used in the P-38? Do we know how they performed in the P-38?
I always assumed the accuracy of the two weapons the same.Which important meeting? the Navy Requested 23,326 T-31 20mm guns on the 12th of February 1944, this is the gun that wound up standardized as the M3 Hispano. According to Chin "ALL" future Navy aircraft designs (at the time) would use this gun. This predates the fighter conference by 8 months?
Given equal gun sights there shouldn't be much difference in accuracy. At practical ranges there is little difference in either trajectory or flight time. At 600yds the 20mm Hispano with it's "poorly" shaped projectile has it's first round arrive about the same time as a .50 (firing at 800rpm) has it's second round arrive. According to the P-38 trajectory chart the two guns were within inches of each other to 500yds. The 20mm shells, starting 7 in below the upper .50s hit at the same height (or within an inch) by the time the range was 350-500 yds. you would have to be well beyond 600yds to get any real difference in trajectory. And the higher you go into thinner air the less difference there is.
The accuracy, ie, probability of a hit per projectile, is equal for both the 20mm and 50cal, however the faster firing weapons lands a proportionally greater number of rounds as the accuracy goes up.This makes no sense. why is the "accuracy" of the 50 cal increasing but the 20mm is not? a better gun sight would affect the accuracy of both guns. proportions may change a bit but a better sight is not going to do zero for the 20mm hit probability if makes any significant change to the .50.
Taking the points one at a time,
My copy of the book is out of my reach at the moment so you could be right but my memory was that it was a general statement not a specific breakdown. I do agree that your probability of a hit was done on the variables you mention however using those calculations. However my posting 81 shows a very significant advantage to the 20mm which far outweighs the additional hits obtained by the 0.5 which has to rely on hitting a vulnerable part whereas the 20mm is almost certain to do damage wherever it hits.
I don't see the attendance at the conference of C. A. Lindbergh being of relavence to this as he isn't a gunnery expert.
Do you have any 20 mm and/or 50 cal ballistics data. I am confused by the Navy comment on kinetic energy at a 500yd target as the 20 having 2.5 times the 50 cal. yet the gun having three times the horsepower. I can only believe that ballistic changes would cause this, or my lack of understanding.
Certainly, in ww2 the HS 20mm was superior in performance where two 20s balance six .50s, except when a gun jams where 50% of the firepower of the 20s would have been lost, and its inclusion would have improved performance because of reduced weight. However, in the book and historically, there seem to be no great enthusiasm among the combat commanders or the war fighters to replace the 50 in the Navy, whose tech staff did prefer it and did update after the war, and certainly in the AAF. This may have been due to poor performance of the M-2 cannon. Also, as far as I know, there seemed to be no great enthusiasm with the British, who had experience with the 20s and had a better cannon, to upgrade their F4Fs, P-51s, F4Us, or F6Fs, to 20mm even though they did upgrade the P-51 with other weapons(I believe a rocket launcher), the Malcolm hood and test advance engines, and clip the wings of the F4Us, all to improve performance. I am being redundant here with another thread.
I understand what you are saying but kinetic energy is also part of the energy equation and cannot be dismissed lightly.If I may cut in.
Perhaps we need to make sure about nomenclature.
My take is that USN estimated that one 20mm (Hispano) cannon is equal in aerial combat as 3 .50 cals. So did they mean kinetic energy, or (horse?)power, or whatever scientific metric? Nope, just plain, and, IMO, fairly precise estimate of a weapon's worth in combat. Further, the kinetic energy is a factor in aerial combat, but so is the explosive payload. And a projectile carrying payload is far less susceptible to the loss of velocity over bigger distance, than a bullet that relies on speed to make damage.
I said this poorly "replace the 50 in the Navy, whose tech staff did prefer it and did update after the war". I meant to say that the tech staff preferred upgrading the 50 to 20 mm and did update after the war.As for Navy tech staff not prefering the cannon over HMG:
- that declaration could use some good source
Oct. '44, some of the most vicious and deadly fighting using these "left over aircraft" was yet ahead for the allied forces in the Pacific, and the Navy was about to field the most powerful fighter it would field in the war, the F4U-4, with 50s.- what should be a reason for major update of WW2 left-overs?
With the F4U-4C it tried out the American gun, I think, and it was a failure. The Post war F4U-5 also came with 20mm, but I don't know which one.- the Panther used cannons in Korean war, so quite soon after WW2 ended
I was not complaining about the jamming sensitivity of the 20s. I was comparing six 50s to two 20s. With one gun jam, the six 50s only lose a sixth of its fire power, the 20s, however, lose half.The jamming issue US produced 20mm cannons had was not shared with 20mm cannons other countries were producing - again no proof that cannon is a worse choice.
four 20s was indeed formidable.Wing clipping and rocket launchers were better choice than full-span wings of Corsair (would'nt fit in hangers) and no rockets at all. As for Malcolm hood, it took only one per plane (and not all the bird-cage Mustangs got it), unlike the cannons, that were 4 needed.
Exactly. The forces that had to make decisions did not feel replacing the 50 cals warranted the effort. They were doing the job.The RAF/FAA didn't rearm their US aircraft I agree probably for the same reason that the USAAF didn't, why should they it was good enough for the job that they had to do. Why go to all the trouble when the original was good enough and you need them ASAP?.
The point is that the British were not adverse to modifying US aircraft to meet some combat or operational need. I don't think they felt they had a need to replace the 50s.I don't think the P51 used rocket in action but could be wrong, the Malcolm hood was needed as the original birdcage wasn't good enough and the F4U's had their wings clipped so they could fit inside the RN carriers whose hangers had less headroom than the USN carriers.
I understand what you are saying but kinetic energy is also part of the energy equation and cannot be dismissed lightly.
I said this poorly "replace the 50 in the Navy, whose tech staff did prefer it and did update after the war". I meant to say that the tech staff preferred upgrading the 50 to 20 mm and did update after the war.
Oct. '44, some of the most vicious and deadly fighting using these "left over aircraft" was yet ahead for the allied forces in the Pacific, and the Navy was about to field the most powerful fighter it would field in the war, the F4U-4, with 50s.
With the F4U-4C it tried out the American gun, I think, and it was a failure. The Post war F4U-5 also came with 20mm, but I don't know which one.
I agree and I must admit that I lack any knowledge of impact of explosive shells.No it can't but then the HE content should not be dismissed lightly either.
Maybe at BuAer, but I have not read anything about desire at ops, even at the Fighter Conference. Of course the Navy was fighting Japanese aircraft that were notoriously vulnerable to 50 cal fire.The Navy was trying to update during the war, perhaps from the beginning of the war.
I fully understand the Navy was moving toward the 20mm. However, to be picky, the FH-1 Phantom initial production contract was placed on 7 March, 1945, with four (!) 50 cals.I have stated this before, from the Fall of 1944 it does not appear that ANY contracts were placed for Navy fighter planes of ANY type ( piston, jet, night fighter) that were not armed with 20mm cannon.
With over 23,000 20mm cannon on order (of the faster firing M3 type) in the spring of 1944 that is enough for 2875 four gun fighters with a complete set of 4 spare guns per fighter. What were they planning to do with these guns if they planned to keep the .50 as the standard gun?