Armor Penetration - 20mm vs. .50 cal.

[Ibuki]

Greetings ladies and gentlemen.

I think you could find this information useful, its in russian, but tables are easy to understand.

http://okirillov.tripod.com/data/rastr/Spravka.htm

Tables № 1 and 2 (табл. №1, табл. №2) show results of aircraft weapons testing which took place in 1947-1948 and 1950-1951. It was a ground testing against actual aircrafts. Сonditions and ranges was set according to «realistic combat conditions». Data in rows shows average number of hits needed to put aircraft out of action.

Some acronyms and translations:
ФЗТ – High Explosive Incendiary Tracer, ФЗ - High Explosive Incendiary, ОЗТ - Fragmentation Incendiary Tracer, ОФТ - Fragmentation Tracer, Ф/ФУГ - High Explosive, МДЗ – Instant Action Incendiary, БЗ – Armor Piercing Incendiary, БЗТ - Armor Piercing Incendiary Tracer, Б-32 – B-32 (12.7mm Armor Piercing Incendiary Bullet)

Б – Boeing, Ту – Tupolev, Пе - Petlyakov, Ла - Lavochkin, Як - Yakovlev, Ил - Ilyushin, МиГ - Mikoyan-Gurevich.

Сзади – from the rear, Спереди – from the front, без учета крыльев – wings don't take into account

А-23, А-44, А-67 – fuse mark. A-23 – probably delayed action, A-67 (aka Б-23) - instant action

Guns:
Н-57 – experimental 57mm cal cannon, НС-37 - NS-37, М-4 - 37mm M4, НР-23 - NR-23, НС-23 – NS-23 (same ammo as NR-23), Г-20 - experimental 20mm cal cannon, Испано – Hispano, МГ-151 - MG 151/20, УБ-12,7 - 12.7mm UB, Оп. 30 мм - experimental 30mm cal cannon, Ш-3 - experimental 23mm cal cannon

http://www.quarry.nildram.co.uk/WW2guneffect.htm
http://www.quarry.nildram.co.uk/modern_fighter_gun_effectiveness.htm

 

[tomo pauk]

The page from the above post, translated by Google:

Translation

Welcome to the ww2aircraft.net, BTW

 

[HoHun]

Hi Clay,

>I still think that a compromise was the best route. Neck up the .50 to .75 and develop a meaningful HE projectile, more ammunition selection in general.

Interesting thought. The German 15 mm MG 151 was transformed into the 20 mm MG 151/20 cannon that way, and the transformation was so successful that after the intoduction of the 20 mm variant, the 15 mm version virtually vanished from fighter use.

I believe the Japanese actually scaled up the entire 12.7 mm Browning (not just the Barrel) to 20 mm with good success, too. I'd have to look it up in Tony's book to see which cannon model this was ...

Regards,

Henning (HoHun)

 

[HoHun]

Hi Colin,

>Doesn't that, by definition, make it a cannon now?

There are different definitions I believe.

One is the capability to fire explosive shells.

The Germans used a definition strictly by calibre ... everything 20 mm and upwards is considered a cannon.

I believe in Tony's book I read about yet another definition that is based on whether the projectiles use driving bands to engage the rifling, but that would make it difficult to categorize a smoothbore gun I'd think

Regards,

Henning (HoHun)

 

[Clay_Allison]

Hi Colin,

>Doesn't that, by definition, make it a cannon now?

There are different definitions I believe.

One is the capability to fire explosive shells.

The Germans used a definition strictly by calibre ... everything 20 mm and upwards is considered a cannon.

I believe in Tony's book I read about yet another definition that is based on whether the projectiles use driving bands to engage the rifling, but that would make it difficult to categorize a smoothbore gun I'd think

Regards,

Henning (HoHun)

I have heard that about the Japanese 20mm, but I have also heard they used (scaled up) the Italian Breda MG design, and have not been able to determine which is true.

 

[Demetrious]

Hi Demetrious,
Hm, I think you should have given me some hint on how you arrived at this idea, but as far as I can tell it's completely wrong.

I speak directly to your comparison of rate-of-fire. I raised no objections to the rest of your analysis. Besides the point Glider raised, of course:

If I read them right, your figures give close to a 1:4 relationship. I find it difficult to believe that the USN and USAAF would be between 35-55% out in their findings.

IIRC, The British found the cannons to be 3X as effective, and the US Navy, 2.5. So your figures showing a 4X advantage are... interesting.

However, even a 2.5X advantage is a 2.5X advantage.

Everything else you said is basic- two Brownings weighted a bit more then a single Hispano, the Hispano threw more firepower, etc. I'm just saying that the ROF analysis should account for two Brownings to a single Hispano, just as the rest of your calculations do.

While I'm at it, I may as well inquire: why didn't more nations, during the war, make more of an effort to go to an all-cannon armament? Most cannon-armed planes I can think of suffered from horribly low ammunition capacities for their cannons. Why didn't they ditch the twin machine guns they invariably carried in order to carry more cannon ammunition? Clearly this is what the US Navy wanted to do. I am at a loss to understand why the German and Russian militaries did not go this route (though the Russians did go all-cannon with the La-7.)

 

[timshatz]

I believe the Japanese actually scaled up the entire 12.7 mm Browning (not just the Barrel) to 20 mm with good success, too. (HoHun)

It makes you wonder, if the Japanese could scale up the M2 to a 20MM and get good results, why the US Military couldn't do it as well. My understanding is they were having trouble with the US "homegrown" 20MM all through the war.

This seems like a simple answer.

Anybody know anything about this?

 

[delcyros]

While I'm at it, I may as well inquire: why didn't more nations, during the war, make more of an effort to go to an all-cannon armament? Most cannon-armed planes I can think of suffered from horribly low ammunition capacities for their cannons. Why didn't they ditch the twin machine guns they invariably carried in order to carry more cannon ammunition? Clearly this is what the US Navy wanted to do. I am at a loss to understand why the German and Russian militaries did not go this route (though the Russians did go all-cannon with the La-7.)

The germans did go into all cannon armement. Most Fw-190A/U used for Sturmstaffeln had their cowl LMG/BMG removed and faired over. So they had 4 x 20mm or 2x 20mm + 2x 30mm all cannon armement. I believe the Me-410 in several versions and the nightfighter, too. Altough mixed cannon armement was common, too.
Later in the war the He-162, Me-262 and Me-163 jet fighters all had uniform main calibre cannon armement, indicating that the GAF made the switch to all cannon armement towards the end of ww2.

 

[tomo pauk]

...
While I'm at it, I may as well inquire: why didn't more nations, during the war, make more of an effort to go to an all-cannon armament? Most cannon-armed planes I can think of suffered from horribly low ammunition capacities for their cannons. Why didn't they ditch the twin machine guns they invariably carried in order to carry more cannon ammunition? Clearly this is what the US Navy wanted to do. I am at a loss to understand why the German and Russian militaries did not go this route (though the Russians did go all-cannon with the La-7.)
...

Actually the russkies did have all-cannon fighter in 1942, the La-5.

I disagree that all-cannon fighters sufferd from the lack of the on-board, ammo, eg. La-5 carried 2x200 rounds. It was the drum-fed cannons that carried typically 60 rounds per gun, but those were not likely to be around from 1942 on.
Also the Hurricane IIC, Typhoon and Tempest were not known to have low ammo count (4X200 rds for the later two planes).

 

[HoHun]

Hi Demetrious,

>I speak directly to your comparison of rate-of-fire.

I have considerable difficulty following your perception of my posts because you seem to respond to stuff I have never written.

Where did I make a comparison of rates-of-fire to which your criticism might apply?

>IIRC, The British found the cannons to be 3X as effective, and the US Navy, 2.5. So your figures showing a 4X advantage are... interesting.

I'm not aware of a British comparison, and the US Navy according to my knowledge and also according to Tony's website saw a 1:3 relation:

"A further validation of the calculations is provided by the outcome of tests by the USN, which stated that the 20 mm Hispano was about three times as destructive as the .50 M2. In the above table, the ratio between their scores is 3.3."

I have pointed out that Tony's calculations slightly underestimate the effectiveness of high-capacity explosive shells in comparison to solid projectiles, and Tony has included the total energy calculations on his site, complete with a comparison table showing the difference between our methods for the Hispano II being only 11%, which I consider excellent agreement. (The differences are greater for German mine shells, for example.)

The figures I quoted above were:

Hispano II: 1.06 MW
12.7 mm Browning: 0.28 MW

This works out to a 1:3.8 relation, not a 1:4 relation. So "HoHun versus The Navy" is not 4 versus 2.5 or 60 % higher, but 3.8 versus 3.0, or just 27 % higher.

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.

The remaining difference of 27 % ... well, what where the Navy's methods and assumptions? An immediate source for differences would be the belting assumed by the Navy for combat aircraft. The RAF's Hispano cannon for a while used solid "ball" ammunition in the mix because production of high-explosive and armour-piercing incendiary rounds wasn't yet able to meet their demands. If the Navy used RAF-style belting for their comparison, the cannon would logically appear slightly less powerful than my calculations, which are based on a 1:1 mix of HE and API for the Hispano and pure API for the 12.7 mm Browning.

>I'm just saying that the ROF analysis should account for two Brownings to a single Hispano, just as the rest of your calculations do.

As far as I can tell, it does. I repeated the calculations in post #109 in this thread, and I don't think you're going to find a mistake there.

Regards,

Henning (HoHun)

 

[HoHun]

Hi Tomo,

>For extra fun: how do you folks rate effectivenes of 37mm cannons ( the US M4 and Russian NS-37 ) for air combat?

Here is a comparison of some cannon with calibres of 30 mm upwards:

MK 108 with 47 rounds (88 kg total), 4,6 MW firepower (52,44 kJ/kg)
MK 103 with 54 rounds (191 kg total), 2,81 MW firepower (14,7 kJ/kg)
VYa-23 with 164 rounds (106 kg total*), 1,2 MW firepower (11,32 kJ/kg)
Ho-301 with 72 rounds (174 kg total*), 2,26 MW firepower (12,98 kJ/kg)
NS-37 with 40 rounds (200 kg total*), 2,17 MW firepower (10,87 kJ/kg)
37mm M4 with 60 rounds (150 kg total), 0,91 MW firepower (6,02 kJ/kg)
,50 Browning M2 with 1000 rounds (165 kg total), 0,28 MW firepower (1,72 kJ/kg)

* weight of belting not included for lack of data

The amount of ammunition is tailored to be equivalent in total muzzle energy to the 1000 rounds of 12.7 mm Browning API included to save as a baseline for comparison.

Oh well, I also made a diagram ... see below.

Regards,

Henning (HoHun)

 

[HoHun]

Hi again,

>Here is a comparison of some cannon with calibres of 30 mm upwards:

>MK 108 with 47 rounds (88 kg total), 4,6 MW firepower (52,44 kJ/kg)
>...

I just noticed I meant to write kW/kg, not kJ/kg! I'm afraid I didn't pay the proper attention to the correct units. This applies to the entire table in the previous post.

Regards,

Henning (HoHun)

 

[HoHun]

Hi again,

Since I liked the way the above graph sums up complex data, I created another one to show machine guns and light cannon, posting it here:

http://www.ww2aircraft.net/forum/te...mparison-machine-guns-light-cannon-17521.html

Have fun!

Regards,

Henning (HoHun)

 

[tomo pauk]

Great stuff, as usual, Henning

Btw, any info about Tony Williams? Hope hi's OK, but we've haven't heard from him a long time.

 

[davparlr]

Do you actually have a price tag for the 12.7 mm Browning vs. the 20 mm Hispano, or are you just making this up? Considering that three 12.7 mm machine guns were needed to replace one cannon, I'd be surprised if it actually was economic at all.

I have no price data on either. Considering that two to three times more M-2 were required for each aircraft, cost, even with construction of a new 20 mm manufacturing facility was probably not a factor. I am sure, due to economies of scale, each M-2 was cheaper than a more limited produced Hispano, but probably not two to three times cheaper.

The lack of reliability of the US Hispano was home-made and avaoidable, and just demonstrates another mistake in US armament development:

Problem would still have to be fixed.

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

That is not a strength of the 12.7 mm Browning, but another failure in US procurement planning. The British with their much narrower industrial base seem to have had few problems to supply enough cannon for the RAF ...

This has nothing to do with the 50 cal or US procurement planning; it is just a reality when an established production line is interrupted with any type of modification. Manufacturing stations must be modified. Production fixtures must be manufactured or modified. Workforce must be trained. All of this must be supported by engineering and documentation and its associated release cycle. Interrupting an existing production line is typically an expense far beyond what is expected. I doubt the British had more efficient production lines than the US.

Actually, I'm surprised that you evade the obvious: 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 Kind 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.

By mid 1942, a useable US 20mm was not assured. I am sure the Navy determined that what they needed was a new aircraft and that modifying and updating the F4F, which would still be marginal, would not be completed prior to the availability of the next generation aircraft, the F4U (carrier suitability was assumed at this time) and F6F. As for implementing the 20mm on those aircraft, there would have been no desire to delay introduction of these superior aircraft without a serious deficiency identified, which there was none regarding the 50cal. Interestingly, ammunition quantity was not increased for these aircraft. I don't think either one of these aircraft is considered a failure because of that decision. The Navy continued to review the use of 20mm and indeed did put it on some ground attack aircraft; however, they must not have felt that the disruption of production lines, down time for deployed aircraft, and increase of logistics, for update of the fighter fleet was warranted, as the 50 cal., while maybe not the optimum configuration, was still devastatingly effective against the enemy. To deem this a failure sixty years later is not reasonable, especially considering the performance historically shown.

The Battle of Midway occurred in 1942. At least try to stay honest, and cut the condescending "Lieutenant Henning" crap.

I am sorry if I came across condescending, although I see how you could take it that way, it was only a pathetic attempt at humor. I am a great admirer of your analysis and weigh your opinions heavily. Please accept my apology.

However, the arguments I made about 1944 were just as valid for 1942, probably even more so, since the US 20mm was very problematic at time. The decision by the US military not to change from a proven weapons system to another without accurate information on kill effectiveness (which was unavailable in 1942, as it apparently is still) would have been irresponsible. As late as 1944, this argument was still unresolved as reported in the Fighter Conference. Here is an insightful quote showing the thought process of the Navy (and the Army), who was starting to favor the 20mm.

I think that was a very good presentation of the arguments against the 20 mm., and it shows the Army's point of view,

-the Army's position was that the 20 mm. would probably be most effective in nose mounted configuration such as the P-38, but that, for the wing mounted installation, they liked the spread targeting afforded by the multiple ranging of multiple guns and the increased rounds delivered of the 50, believing it would the improve the opportunity of hits for the mediocre pilot-

which I have been wondering about for a long time. We are going to let our case for the 20 rest entirely on the way the Fleet wants it. If the 20s are wanted, they will get them; if not, we will stick with the 50's. I think the 20's are coming in here shortly.

Apparently the fleet did not want them as the 20's did not become available until after the war.

The British representative's comment was that they liked the 20 mm. They had determined the optimum size was about .76 cal, based on "statistics for weight of gun, weight of ammunition, velocity, armor penetration, amount of H.E. you can carry and a host of factors like that." 20 mm is a about .77 cal.

Another interesting point was that the British could not clear stoppages in the 20 mm guns.

The mistakes in US weapons procurement

.

A US weapons mistake was not adequately testing torpedoes prior to the war which is testified by the lack of enemy ships sunk. The 50 cal on the other hand, has thousands of down enemy aircraft to testify that the decision to keep the 50 cals was valid. Again, unless you can show something like kills per sortie, and it would have to be significant, your comments are only supposition, not warranting the comment of "failure". I did read in Wikipedia (for what it is worth), that the Germans determined that it took an average of four 20 mm strikes to down a fighter. Now if you could find the average for 50 cals, you may be able to establish a clear position and not just an opinion.

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. I don't know how many Mustangs the Brits flew or how they fought, but, apparently, the 20 mms were not enough of an improvement to warrant updating their P-51s. I guess they felt the P-51 just wasn't hampered enough.

 

[Ibuki]

I did read in Wikipedia (for what it is worth), that the Germans determined that it took an average of four 20 mm strikes to down a fighter. Now if you could find the average for 50 cals, you may be able to establish a clear position and not just an opinion.

Russian tests find that it took 1-2 hits from MG151/20 to down a light fighter (La-7, Yak-3 or P-39). 50 cals needed 10-15 hits. So one MG-151/20 canon was a rough equivalent of six 50 cal machinegun battery and four MG151/20 were equivalent of 24 50 cal machineguns. Hispano was 50% worse than MG151/20 due to weak HE shell.

Of course against tougher targets like P-51 and P-47 numbers could be different.

 

[HoHun]

Hi Davparlr,

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

>>That is not a strength of the 12.7 mm Browning, but another failure in US procurement planning. The British with their much narrower industrial base seem to have had few problems to supply enough cannon for the RAF ...

>This has nothing to do with the 50 cal or US procurement planning; it is just a reality when an established production line is interrupted with any type of modification.

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.

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.

>By mid 1942, a useable US 20mm was not assured.

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.

>To deem this a failure sixty years later is not reasonable, especially considering the performance historically shown.

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.

>I am sorry if I came across condescending, although I see how you could take it that way, it was only a pathetic attempt at humor.

Ah, no offense taken then. Irony somehow does not work as well on the web as it works in personal conversation - I have had irony back-fire on me like that too, and more than once :-/

>However, the arguments I made about 1944 were just as valid for 1942, probably even more so, since the US 20mm was very problematic at time.

I can see your point regarding lead times. However, it still comes down to a failure to have a 20 mm cannon ready for (say) Midway, where a cannon-armed F4F would have enjoyed undeniable and important advantages over a machine-gun armed F4F. Even if we consider it impossible to the Hispano cannon to be made ready in time, US procurement also failed to have an indigeneous US cannon developed, or simply a foreign cannon built under license. 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.

>The decision by the US military not to change from a proven weapons system to another without accurate information on kill effectiveness (which was unavailable in 1942, as it apparently is still)

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. 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.

>Another interesting point was that the British could not clear stoppages in the 20 mm guns.

Do you mean "clear stoppages in flight"?

>The 50 cal on the other hand, has thousands of down enemy aircraft to testify that the decision to keep the 50 cals was valid.

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.

>Again, unless you can show something like kills per sortie, and it would have to be significant, your comments are only supposition, not warranting the comment of "failure".

Don't fool yourself - the firepower and the weight of the guns in question can be calculated rather easily, and there is no way around energy as key parameter for destructiveness. The superiority of cannon is so great that any approach based on the physical parameters of the guns will show it, and in fact Tony's "traditional" approach shows it as well. 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.

The Bad Eilsen comparison shows that the Germans considered the 20 mm shells 3.75 times as effective as the 15 mm projectiles against bombers, and in direct comparison to the 12.7 mm gun, the 15 mm weapon fired a projectile of 150 - 160 g at 850 - 960 m/s, compared to the 12.7 mm's 112 g at 890 m/s. Accordingly, the 20 mm Mauser was vastly superior to the 15 mm Mauser which was markedly superior to the 12.7 mm Browning (so much that the US copied it with the intention of replacing the 12.7 mm Browning).

In terms of total muzzle energy, the 20 mm mine shell (found to be highly effective against fighters by the Germans) has about 6.0 - 6.5 times the value of the 12.7 mm Browning API projectile, which means that the energy comparison matches the German Bad Eilsen documents well. The belting instructions from the Schießfibel, showing that the best belting against fighters includes a higher proporition of mine shells than the best belting against bombers (putting to rest the myth of mine shells being dedicated anti-bomber armement), validates the assumption that against fighters, high explosive projectiles are (particularly) effective.

(In my calculations, I'm using the 13 Sprgr.L.zgr.:M-Gesch. mix recommended by the Schießfibel, so the total energy factor over a pure 12.7 mm API belting is only 4.4 on the average.)

I don't see any way someone could come up with a different method of comparing firepower based on the physical realities that would yield a radically different picture from the results Tony and I have determined.

Regards,

Henning (HoHun)

 

[HoHun]

Hi Ibuki,

>Russian tests find that it took 1-2 hits from MG151/20 to down a light fighter (La-7, Yak-3 or P-39). 50 cals needed 10-15 hits. So one MG-151/20 canon was a rough equivalent of six 50 cal machinegun battery and four MG151/20 were equivalent of 24 50 cal machineguns. Hispano was 50% worse than MG151/20 due to weak HE shell.

Highly interesting data! Do you know the kind of shell was used by the MG 151/20 for the test?

Were the hits "randomly distributed", or were the guns aimed at (for example) the fuselage? I'm asking because the British conducted a test of the 30 mm MK 108 in which a single shot was fired at Spitfire fuselages.

(The Germans established that the effect of mine shells was greater against the wings than against the fuselage due to the smaller expansion space provided for the blast.)

Regards,

Henning (HoHun)

 

[Demetrious]

Hi Demetrious,

I have considerable difficulty following your perception of my posts because you seem to respond to stuff I have never written.

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.

I am tremendously interested in this little quote of yours, because it seems to be making a direct comparison between the 12.7mm and the 20mm, "the probability of a hit for a single round." Now, if you're comparing two Brownings to one Hispano, that means there are 27 bullets in the air per second of fire for the Brownings compared to 10 cannon shells for the Hispano. 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.

The rest of your calculations make sense, they're done from a number-of-guns standpoint as regards throw weight and ammunition supply/duration.

I'm not aware of a British comparison, and the US Navy according to my knowledge and also according to Tony's website saw a 1:3 relation:

That was said earlier in the thread, and I've heard the same thing quoted elsewhere. 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.

To be honest, I can't tell which is which anymore; it's very confusing. But it would make sense, however, if the US Army's comparison found it to be 2.5, and the Navy, 3.0, which would explain why the Navy wanted to switch to all-cannon armament and the Army did not.

So "HoHun versus The Navy"

Actually, to be fair, I would have said it was "HoHun vs. the British" and their x3 value- based on the principle of charity, after all.

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?

If the Navy used RAF-style belting for their comparison, the cannon would logically appear slightly less powerful than my calculations, which are based on a 1:1 mix of HE and API for the Hispano and pure API for the 12.7 mm Browning.

Standard belting practice for the 20mm in the P-38 was two tracer, two AP, and two HE, if memory serves, so I suspect they would have done the same for their trials.

As for the rest of this, I think the primary objection most people have to your statements is the rather bold claim that the failure to procure cannon was a serious, dangerous failure on the part of the US Navy. If I understand this right, you are implying that the 12.7mm gun was insufficient and nearly failed the US Navy. I don't know to what extent you share Admiral King's views on that.

However:

However, it still comes down to a failure to have a 20 mm cannon ready for (say) Midway, where a cannon-armed F4F would have enjoyed undeniable and important advantages over a machine-gun armed F4F.

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 machine-gun armed F4F was more then good enough, however- it had guns that dealt out more then enough firepower to down it's principle opponent and had good ballistic properties. You seem to be implying that you agree with Admiral King in that the Browning was dangerously insufficient, and that's what most people here seem to be baffled by. Can you clarify on this?

As for numbers: let me demonstrate why I don't trust numbers to tell the whole story. Consider this: if you kill the pilot, you have destroyed both the plane and a trained enemy aviator. It only takes one bullet to penetrate the cockpit to kill the pilot. Now, the .50 cal gun was just as likely to penetrate armor as was the explosive 20mm round, (about 20mm was the value given earlier in this thread.) So, the Browning batteries, putting out twice the number of projectiles, had twice the probability of landing hits on the armored cockpit, and thus twice the probability of killing the pilot and destroying the aircraft.

A horrible over-simplification, but hey, it sounds good!

 

[Ibuki]

Highly interesting data! Do you know the kind of shell was used by the MG 151/20 for the test?

Stated ФУГ (ФУГасный) – High Explosive, same for Hispano (Ф - Фугасный).

Were the hits "randomly distributed", or were the guns aimed at (for example) the fuselage? I'm asking because the British conducted a test of the 30 mm MK 108 in which a single shot was fired at Spitfire fuselages.

Not specifically stated but looks like randomly distributed, except for Il-2 testing. During that testing «wings were not taken into account»

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