How would you have armed the P38 if you were to use it as it was used historically?

[Lighthunmust]

"How many passes would've required 3-4 dozens of .50cal ammo?"

You'd have 6.1 seconds of firing time to expend the low end of 36 rounds (3 Dozen) from one M-2 Browning set to fire at 400 r.p.m. Regards

This is a really complex issue. It will take a great amount of research time to adequately find answer. A couple of things though: 400 rpm per M2 seems a bit low, firing time for a frontal attack is 1.5 seconds according to Mike Spike's diagram and text, number of guns firing, what methodology did the LW use to determine hit percentage and specifically did they include all angles of attack to derive this number, etc.

 

[Shortround6]

So far I believe it looks large in tables and graphs of projectile power and individual weapon cyclic rates, and not so much in actual use. Part of the problem is we don't have many reports of 6/8 gun American fighters attempting to shoot down strongly build, heavily armed, four engined bombers. I wonder why? What I am finding is German accounts of shooting down bombers in one firing pass being atypical. It taking multiple firing passes to force bombers out of formation and then finishing them off. I am finding accounts of the Germans believing hits from twenty 20mm shells or three 30mm shells being necessary to destroy a heavy bomber. I also find accounts of Germans having a 2-4% hit percentage. Sources claim that some of the German cannons equal the cyclic rates of the M2. One of these source usually lists a single rate for the cannons, but a slow and fast rate for the M2. This makes we wonder about a level playing field of primary sources and testing. I am still working on determining what the balance point is between weapons with smaller amounts of devastating projectile power and weapons with larger amounts of sufficient projectile power. To the best of my knowledge, no one has address the actual firing reliabilty of the German cannons or the engagement times of single engine fighters attacking the bombers. I don't consider those over loaded FW190s fighters, they were bomber destroyers and sitting ducks for true fighters. Consider this; would the P-38 mock-up with 12 .50s been an even better bomber destroyer than the cannon armed FW190? It also would cease to be a fighter and become a sitting duck. I have actually fired and M2s and a Dshk, and seen upclose the what hits from .50s and 20mms do to lightly armored targets. The .50s destroyed the targets ability to function, the 20mms destroyed the target. The 20mms did it from the altitude of an AC-130, the .50s from 1000 yards. Either results in a kill if the targets were flying at 20,000 feet. WW2 aerial air to air engagements were rarely more than half of a 1000yards.

Of course installation and environment affected M2 functioning, but I suspect that all those wonderful cannons were much more adversely affected as were the aircraft that mounted them. Here is an example: It is my understanding that on one of the late mark Spitfires they had to remove two of the four 20mms and replace them with .50s because of aircraft flight handling issues. I'm sure shortround6 can find the details faster than I can. He has an amazing ability to post detailed specifications and dates of events. I am wondering about him being a professional aviation writer or some kind of aviation savant. I suspect he has a very good idea of what a .50cal projectile can do.

First, let me thank yo for the kind words. I just have done some reading and collecting of books on few subjects like guns and engines, There are many people on this Forum whose knowledge in many areas of WW II aircraft far exceeds mine.

Back to the subject at hand.
There is no question that the .50 is a very powerful round compared to what most of have had any experience with. It is roughly 4 time more powerful than a .30-06

There is no question that it can do a lot more damage than rifle caliber rounds to armor, masonry walls, trees engine blocks,etc. the problem with comparing it to "THE" 20mm is "WHICH" 20mm are you comparing it to and how?

A short and abbreviated list of muzzle energy in Joules, courtesy of Tony William's book "Flying Guns World War II".

RiflecaliberMGs.........................3,270-4,140
Italian/IJA 12.7........................10,600
American .50...........................17,400
Russian 12.7............................19,200
German 13................................9,700
IJN 20 type 99-1.......................23.000
German 20 FF..........................19,700-24,100
German 20/151........................29,000-29,400
IJA HO-5 20.............................21,000-29,000
Russian 20..............................36,000
IJN type 99-2...........................36,000
Hispano 20..............................46,900-50,300
German 20 X 138.....................60,500

Again this is kinetic energy at the muzzle. Some projectiles could loose up to 38% of their velocity by the time they traveled 300 meters depending on type and shape. The .50 was very good in this regard being among the best if not "THE" best at retaining velocity. From a pure 'striking' power with kinetic energy at normal combat ranges (1000yd shots are best left to flight simulation games) the .50 actually compares rather well with some 20mm rounds. Especially considering rates of fire. How much energy can be delivered per second?
However we can also see that the Hispano was practically in a class by itself, being about 30% more powerful than any other commonly used aircraft 20mm gun. The German 20 X 138 was an anti-aircraft/tank/anti-tank round that was only used in a small run of heavy-slow firing aircraft guns in the late 30s. The Hispano has almost 3 times the kinetic energy of the .50 cal and so is going to do that much better at smashing engines, breaking ribs, spars, attachment flanges,etc.
Of course this is with solid shot (which the British did use when they had problems with early fuses) and does not consider the dynamic of the HE filler.

With the He (or HE+incendiary) we have 3 things to consider that the .50 essentially skips.
1. The amount of HE filler, which varied from 3.7 grams to about 10 grams for most shells with the German M-Geschoss jumping to 20 grams and above.
2. The fusing. does it allow the shell to penetrate or does it blow up on contact, making an impressive hole on the skin but not damaging the internal vital parts of the aircraft.
3. The fragmentation of the 20mm projectile. A German 'mine' shell weighed 92 grams with 20 of that being the HE, take out the weight of the fuse and there isn't a lot of metal to turn into fragments that can cut/pierce nearby wires/lines/cables. Japanese Army 20mm projectiles weighed 79 grams with about 8-12 grams of filler and were in the same boat. Heavier (127-130 gram) projectiles with around 10 grams of filler have a lot more metal flying around after the explosion to cause secondary damage, even if only a few feet from the explosion site.
3-A. Light 20mm shells with high HE content don't penetrate very well. While a heavy shell with thick walls 'can' be fused to penetrate heavy structure or light armor and detonate behind it, a thin wall shell will breakup and fail to penetrate regardless of the fuse.

As can be seen trying to compare the .50cal to 20mm guns is very difficult because of the variety of 20mm rounds and ammunition.

And we haven't even gotten to the rates of fire and guns weights yet

 

[Rivet]

"400 rpm per M2 seems a bit low"

This in the interest of accuracy. Much to be said for a weight of fire on target, not having to fight the recoil increases ability to aim.

 

[Shortround6]

"400 rpm per M2 seems a bit low"

This in the interest of accuracy. Much to be said for a weight of fire on target, not having to fight the recoil increases ability to aim.

Ah, isn't the gun bolted to the airframe in some fashion? Fighting the recoil might only apply to a hand aimed gun like a piviot mount on a jeep or a waist gun. If firing at 800rpm throws the aim off that much in a fixed gun you need a new airplane.

That said some early war .50s did cycle at about 400rpm in synchronized installations. But that has to do with starting with a 600rpm gun, adding the synchronizers and figuring in belt drag.

 

[johnbr]

How about the 6 Mauser 215 guns in the P38.

 

[gjs238]

I am still working on determining what the balance point is between weapons with smaller amounts of devastating projectile power and weapons with larger amounts of sufficient projectile power.

Kinda like the .308/M-14 vs. .223/M16 debate that's been raging for decades.

 

[renrich]

This is a highly interesting debate. Good work by many. All along I have been an advocate of " Old Ma Deuce" perhaps because I fired one on the range at Fort Hood and saw what it could do to old deuce and a halfs and half tracks. Does anyone believe that any WW2 aircraft was built more solidly than those vehicles?

Having said that, I realise that the USN, on their ships, started the war with a lot of fifties in their AA suites and quickly substituted 20 mms and 40 mms for those fifties. They did that because they needed to knock down the attackers now. One factor in those cases was that the shots were usually head on or deflection shots, not from the rear aspect like most aviation kills. That factor raises an interesting question which I don't have the answer for.

When hunters are after dangerous large thick skinned game they generally use solids rather than expanding bullets because they want the projectile to penetrate deeply, maybe go through bone rather than expand quickly. Likewise fmj bullets in modern military rifle caliber bullets often zip right through the target and don't do nearly as much damage to a leg, arm or even the body as a dum dum bullet or the massive relatively blunt, lead minie ball of the War of Northern Aggression.

Here comes the question. I believe that the various cannon shells had a fuse which caused the internal explosive charge to explode when the projectile made contact with the target. Is it possible that in some cases a hit on the skin of the after fuselage of an aircraft or the skin on a wing by a cannon shell would cause the explosion which would cause a hole in that skin but perhaps no further damage where as a kinetic energy bullet like the 50 BMG would zip through the skin and continue more deeply into the fuselage or wing, possibly causing damage to a radio, oil cooler, oxygen bottle, control cable, radiator, etc. ???

Don't misconstrue what I am asking. I have no doubt that, on average, a hit from a 20mm would be more destructive than a hit from the 50 BMG but I am wondering if the destructiveness of the WW2 20mms compared to the WW2 50 BMGs might be overstated as far as air to air combat is concerned. If it is, the relative lethality of the 50 BMGs in WW2 because of number of guns carried, rate of fire, ammo carried, reliability, etc., might be much better than we realise.

Another point which I don't believe is well understood by many of us is that the way guns were bore sighted in WW2. They were not always regulated to converge on a single point at a certain range. According to pilot preference or unit policy, some were regulated to produce a "box" pattern at perhaps 300 yards, some were regulated where the inboard guns converged at a fairly close range, the middle guns further away and the outboard guns even further. The nose mounted guns of the P38 could be sighted to give a fairly wide pattern at 300 yards. I have also read that many pilots of Corsairs would turn off two guns and use the four remaining guns ammo before turning back on the other two.

 

[tyrodtom]

If the cannon fuze can trigger the explosion even in 1/1000th of a second, the shell will have traveled maybe 2 feet before it explodes. That's if it hits something flimsy like the outer skin, if it hit any of the structual members, of course it would slow down more. In some cases the outer skin probably wouldn't even trigger the fuze.

There's a lot of variables, fuze sensitivity, and fuze initiation speed, which i'm sure they were doing a lot of experimenting on.

I was pretty involved with munitions in the mid to late 60's. But i've got a lot to learn on the WWII varietys.

 

[Lighthunmust]

If the cannon fuze can trigger the explosion even in 1/1000th of a second, the shell will have traveled maybe 2 feet before it explodes. That's if it hits something flimsy like the outer skin, if it hit any of the structual members, of course it would slow down more. In some cases the outer skin probably wouldn't even trigger the fuze.

There's a lot of variables, fuze sensitivity, and fuze initiation speed, which i'm sure they were doing a lot of experimenting on.

I was pretty involved with munitions in the mid to late 60's. But i've got a lot to learn on the WWII varietys.

Another variable would be the "dud" percentage. A percentage that may climb if the living conditions of the work force decline. It is my understanding that the Germans did have the technology to fuze their 20mm and 30mm shells to perform as desired. What they needed was a good proximity fuse.

 

[Shortround6]

Another variable would be the "dud" percentage. A percentage that may climb if the living conditions of the work force decline. It is my understanding that the Germans did have the technology to fuze their 20mm and 30mm shells to perform as desired. What they needed was a good proximity fuse.

Since it took some time into the 70s (80s?) to get a proximity fuse into a 40mm shell I think this one is a non starter for WW II aircraft cannon.

With a blast radius measured in single digit feet (and low digits at that) Proximity fuses for 20-30mm shells are not really a worthwhile idea.

 

[Readie]

Since it took some time into the 70s (80s?) to get a proximity fuse into a 40mm shell I think this one is a non starter for WW II aircraft cannon.

With a blast radius measured in single digit feet (and low digits at that) Proximity fuses for 20-30mm shells are not really a worthwhile idea.

Did Anti Aircraft shells have proximity fuses or where they triggered by attitude / time?
Cheers
John

 

[Lighthunmust]

Since it took some time into the 70s (80s?) to get a proximity fuse into a 40mm shell I think this one is a non starter for WW II aircraft cannon.

With a blast radius measured in single digit feet (and low digits at that) Proximity fuses for 20-30mm shells are not really a worthwhile idea.

Did Anti Aircraft shells have proximity fuses or where they triggered by attitude / time?
Cheers
John

Didn't American 40mm shipborne AA have proximity fuses? I also seem to recall American 90mm AA had them.

My understanding is that most fuses were triggered by time of flight to altitude for AA.

 

[Shortround6]

AA shells started with time fuses, the British were developing the proximity fuse and passed it to the US. Since it took mini-vacuum tubes (valves) and special batteries to make it work it took up a lot of volume in the shell. British and US used it in 90mm and bigger AA shells but got it into 3in/75mm by the wars end. The AA troops were not allowed to US proximity fuses where there was a chance of the Germans capturing them until sometime in 1944 when it would have been too late to copy them.

 

[Shortround6]

Didn't American 40mm shipborne AA have proximity fuses? I also seem to recall American 90mm AA had them.

My understanding is that most fuses were triggered by time of flight to altitude for AA.

Maybe in the 70s or 80s the 40mm had proximity fuses.

 

[Lighthunmust]

AA shells started with time fuses, the British were developing the proximity fuse and passed it to the US. Since it took mini-vacuum tubes (valves) and special batteries to make it work it took up a lot of volume in the shell. British and US used it in 90mm and bigger AA shells but got it into 3in/75mm by the wars end. The AA troops were not allowed to US proximity fuses where there was a chance of the Germans capturing them until sometime in 1944 when it would have been too late to copy them.

According to Wikipedia (yes I know) they were used by U.S. artillery during the Bulge. Supposedly terrified German infantry who nearly mutinied. I will do some more fact checking.


According to an article on the Naval Heritage website of the U.S.N. they successfully tested the first fuses in 1941 using among other weapons a 37mm cannon. This may or may not mean that a 40mm proximity fused shell was possible just not economical to mass produce. Gotta do some more digging.

 

[Shortround6]

See; http://www.history.navy.mil/faqs/faq96-1.htm

37mm gun was used to launch test components to see if they would stand the shock of firing, not with the idea of coming up with a workable projectile in that caliber.

Early proximity fuses took up enough room that some shells were provided with a removable explosive element that was taken out when the Proximity fuse was used and left in when normal time fuses were used.

And "In addition to the development of the Mk 33 fuze for the British, another fuze known as the Mk 41 was also produced. This latter fuze was designed primarily for the British 4" gun carried aboard destroyers, and differed from the Mk 33 in that its size was still smaller. This was necessary because the 4" projectile was too small to accommodate the Mk 33 fuze and still leave sufficient quantity of explosive."

"Consequently, a Mk 45 fuze was produced for the 3"/50 in about May of 1944. This fuze was delivered to the Fleet, but was never very satisfactory and its production was ultimately discontinued. A new fuze, known as the Mk 58, was designed for the 3"/50 which contained more or less the standard Mk 45 design with the addition of a wave suppression feature to permit use of this fuze low over waves. The Mk 58 fuze was delivered to the Fleet in November 1944."

 

[Lighthunmust]

Shortround6 I sent you a PM

 

[fastmongrel]

Shortround I have come across some mentions of Canadian work on VT fuses but never found any details. Did the Canadians ever get a working fuse into production.

 

[renrich]

Another example of what I am talking about is the British experience at Jutland. It is said that the relatively poor performance of the heavy caliber AP British shells compared to the German was that either because of poor fuse performance or unstable internal explosive material, the Brit APs exploded on the surface of the target's armor plate whereas the German's APs internal explosive did not detonate until after the shell penetrated inside the armor plate. An extreme example but illustrative of the factor which might hinder lethality of aerial cannon shell.

 

[Lighthunmust]

See; http://www.history.navy.mil/faqs/faq96-1.htm

37mm gun was used to launch test components to see if they would stand the shock of firing, not with the idea of coming up with a workable projectile in that caliber.

You are absolutely right! I obviously skimmed that article way to fast. The relevant passage:

"It was soon decided that the best way to test tubes and other components for ruggedness was to actually fire then from a gun and recover them to examine for extent and causes of failure. Early in 1941, experiments were carried out in which tubes were mounted in blocks in a 5"/38 projectile arranged for parachute recovery. Other means of recovery firing were also undertaken. A smooth bore gun was made out of a piece of gas pipe and set up in a farm yard for testing of tubes and components. This gun was fired vertically and the projectiles, which were homemade, fell back in the field where they could be recovered and disassembled. This gun was later superseded with an Army 37mm gun used for recovery firing.

Concurrently, circuit work was carried out in the laboratory. Also, functioning oscillators were mounted in projectiles and fired in attempts to get functioning in flight. Both the 5"/38 and the 37mm guns were used in these tests. Radio receivers were used in an attempt to hear the signal from the oscillator during flight. As a source of power for the unit in the 5"/38 projectile, special batteries built by the National Carbon Company for the bomb fuze were used. For the unit in the 37mm projectile, a special battery was built using National Carbon Company's minimax cells for B-power and pen-light cells for A-power. At about the end of April 1941, an oscillator fired in the 37mm gun was actually heard throughout flight."

Thanks for catching that Shortround6.