What was the air to air weapon, or combination of weapons, used in WWII?

[Greyman]

I agree that I am largely speculating with my figures for the .50

You are exceedingly close to the actual figure at which the British arrived (for a Heinkel 111). When I get a few minutes tonight I'll try and relay the figures.

EDIT:

Alright, basically it broke down to this:

25% chance of Lethality
20 mm HE/I - 4 rounds
.5 inch AP - 11 rounds
.303 inch - 24 rounds

50% chance of Lethality
20 mm HE/I - 9 rounds
.5 inch AP - 20 rounds
.303 inch - 42 rounds

75% chance of Lethality
20 mm HE/I - 17 rounds
.5 inch AP - 33 rounds
.303 inch - 67 rounds

90% chance of Lethality
20 mm HE/I - 29 rounds
.5 inch AP - 50 rounds
.303 inch - 105 rounds

The tests were based on ground-firing trials against a Heinkel III, 200 yards direct astern and assumed a uniform distribution of strikes over the airframe.

The British analysts remarked that the figures were probably slightly pessimistic due to the impossibility to simulate airframe disintegration (lack of air stresses) and it was not possible to assess on a statistical basis the myriad of ways a fire could start due to engine behavior under fire.

During the test they didn't have proper stats on the likelihood an HE/I round would set a petrol tank on fire. Based on four strikes, the tank lit up once, so they went with 25%.
Afterwards they were able to do more extensive tests and found this was 40% (this time based on 60 strikes). This was indicated in an addendum to the firing trial.

Also, fuel leaks were not factored in. The thinking was that German bombers operate from such short distances to their targets, the chance of petrol tanks being holed and emptied was removed. I would think this would hurt the Hispano numbers more than the two Brownings.

---

Your 'two percent' hit accuracy figure sounds reasonable to me as well, as the figure I think I've generally run into is about one percent accuracy. If you were isolating the statistic against large bombers that weren't maneouvreing, a doubling of hits would seem to fit.

 

[zjtins]

Yet, you admit that you've nothing to go on but youtube videos of gun camera footage highlights, which neither know the speed of or which aircraft were doing the firing.

Not sure how you can conclude that when I specifically talked about books from pilots from WWII and compared the results as being similar.

I tried several national archives but several have been turned off after 911 you have to have a clearance now. If you know of one that is still open I will research it.


Greyman now that is interesting data, I assume lethality as likelihood of bomber going down.

But it shows the ratio for number of 50.cal to 20mm rounds reducing for a greater liklehood of shootdown.
25% 2.8
50% 2.2
75% 1.9
90% 1.7


Assuming the ROF for the .50 and 20mm were close then

2x20mm 4x20mm setup vs 6 and 8 gun .50cal setup @50% lethality

2x20mm 0.7 and 0.6 of 6 and 8 gun
4x20mm 1.5 and 1.1 of 6 and 8 gun

So a 2 x20mm is worse than a 6 or 8 gun .50 but 4x20mm is better.

But to give an idea of other factors influence, when the Germans went to the gyro sight they claimed a 30% increase in hit probability.
30% is around the delta between the 2x20mm and 6 gun .50 and more than the delta between the 4x20mm and 8 gun .50 cal setup.

Also the longer the shooting the less the difference to bring the Heinkel down. Granted we don't know the wind/loading affects and the 20mm has an advantage there but unless its is major impact then its just another complicating factor.

 

[RCAFson]

90% chance of Lethality
20 mm HE/I - 29 rounds
.5 inch AP - 50 rounds
.303 inch - 105 rounds

.

The effectiveness of the .303 is interesting; if we assume 14rps for the .5in and 20rps for the .303, it would seem that 8 x .303 is roughly equal to 6 x .5in, yet the 8 x .303 battery is much lighter, ditto for 4 x 20mm cannon at 10rps.

 

[zjtins]

The effectiveness of the .303 is interesting; if we assume 14rps for the .5in and 20rps for the .303, it would seem that 8 x .303 is roughly equal to 6 x .5in, yet the 8 x .303 battery is much lighter, ditto for 4 x 20mm cannon at 10rps.

Now you get it!

The P-47 was big and had a huge engine and could lug 8x50cal. The rest of the AF/Navy (generally) had 6x.50 and had engines big enough to lug them around.
The Spit was too sluggish with 4x20mm as was the ME-109 with more than the 1x20mm and 2 MG.

There were all kind of tradeoffs each country/AF had to make for their situation. They had constraints they just could not build what every they wanted, plus political infighting, plus not having hard data. All sides were way off in both actual kills and enemy estimates. How does one select a weapon/weapon system or setup when the input so cloudy?
BTW the Typhoon (?) I think was the fighter had 12X.303 until they got some 20mm available. I could not find any record of combat with it.

However the range the .303 in terms of bullet momentum dropped off much faster than the .50 cal AP so range would be a bigger factor in combat that was not measured.

I can prove it but that seems to be a big problem in the BoB as it appear that many novice pilots opened up at too great a distance, losing momentum, surprise and not a the optimum distance for the gun angles.

 

[Greyman]

A couple more things I forgot to add about the test, things that would hurt the 20-mm numbers more than the others'.

During the test they didn't have proper stats on the likelihood an HE/I round would set a petrol tank on fire. Based on four strikes, the tank lit up once, so they went with 25%.
Afterwards they were able to do more extensive tests and found this was 40% (this time based on 60 strikes).

Also, fuel leaks were not factored in. The thinking was that German bombers operate from such short distances to their targets, the chance of petrol tanks being holed and emptied was removed. I would think this would hurt the Hispano numbers more than the two Brownings.

I'll edit the original post and add this info as well.

 

[CobberKane]

Not sure how you can conclude that when I specifically talked about books from pilots from WWII and compared the results as being similar.

I tried several national archives but several have been turned off after 911 you have to have a clearance now. If you know of one that is still open I will research it.


Greyman now that is interesting data, I assume lethality as likelihood of bomber going down.

But it shows the ratio for number of 50.cal to 20mm rounds reducing for a greater liklehood of shootdown.
25% 2.8
50% 2.2
75% 1.9
90% 1.7


Assuming the ROF for the .50 and 20mm were close then

2x20mm 4x20mm setup vs 6 and 8 gun .50cal setup @50% lethality

2x20mm 0.7 and 0.6 of 6 and 8 gun
4x20mm 1.5 and 1.1 of 6 and 8 gun

So a 2 x20mm is worse than a 6 or 8 gun .50 but 4x20mm is better.

But to give an idea of other factors influence, when the Germans went to the gyro sight they claimed a 30% increase in hit probability.
30% is around the delta between the 2x20mm and 6 gun .50 and more than the delta between the 4x20mm and 8 gun .50 cal setup.

Also the longer the shooting the less the difference to bring the Heinkel down. Granted we don't know the wind/loading affects and the 20mm has an advantage there but unless its is major impact then its just another complicating factor.

On the whole the info would seem to be compatible with the LW and USN conclusions. The LW were looking at the average number of 20mm hits required to bring down a bomber, so their conclusion of twenty hits would correspond to the British findings for 50 percent lethality. The Brits found it took nine hits to achieve 50 percent lethality on an He 111, the Germans concluded that it took twenty hits to achieve the same on a B-17, which would make the four engine bomber a little more than twice as tough as the twin. Halve it again and you get 4-5 (12-15 .50 cal) hits fot a fighter, again in the ballpark.
As you point out, at 50 percent lethality it takes 2.2 .50 rounds to do the work of one 20mm, so the USN idea of one 20mm cannon being equal to about three .50 cals is also supportable, particularly given the factors Greyman mentioned that may has penalised the 20mm somewhat.
What isn't considered here is the lethality of the weapons in proportion to weight. I haven't done the sums but I'm betting that one 20mm with ten seconds of ammo would weigh quite a bit less than the equivalent three .50 cals with the same firing time (or even a bit less ammo if the .50s higher ROF would allow it to score the required number of hits in less time). If that's so, to my mind the 20mm is clearly the better weapon once the battle is joined, but this does not invalidate the US decision to stick with the .50 given its demonstrated effectiveness in the use to which it was being put, logistical considerations etc.

 

[Jabberwocky]

You are exceedingly close to the actual figure at which the British arrived (for a Heinkel 111). When I get a few minutes tonight I'll try and relay the figures.

EDIT:

Alright, basically it broke down to this:

25% chance of Lethality
20 mm HE/I - 4 rounds
.5 inch AP - 11 rounds
.303 inch - 24 rounds

50% chance of Lethality
20 mm HE/I - 9 rounds
.5 inch AP - 20 rounds
.303 inch - 42 rounds

75% chance of Lethality
20 mm HE/I - 17 rounds
.5 inch AP - 33 rounds
.303 inch - 67 rounds

90% chance of Lethality
20 mm HE/I - 29 rounds
.5 inch AP - 50 rounds
.303 inch - 105 rounds

The tests were based on ground-firing trials against a Heinkel III, 200 yards direct astern and assumed a uniform distribution of strikes over the airframe.

The British analysts remarked that the figures were probably slightly pessimistic due to the impossibility to simulate airframe disintegration (lack of air stresses) and it was not possible to assess on a statistical basis the myriad of ways a fire could start due to engine behavior under fire.

During the test they didn't have proper stats on the likelihood an HE/I round would set a petrol tank on fire. Based on four strikes, the tank lit up once, so they went with 25%.
Afterwards they were able to do more extensive tests and found this was 40% (this time based on 60 strikes). This was indicated in an addendum to the firing trial.

Also, fuel leaks were not factored in. The thinking was that German bombers operate from such short distances to their targets, the chance of petrol tanks being holed and emptied was removed. I would think this would hurt the Hispano numbers more than the two Brownings.

---

Your 'two percent' hit accuracy figure sounds reasonable to me as well, as the figure I think I've generally run into is about one percent accuracy. If you were isolating the statistic against large bombers that weren't maneouvreing, a doubling of hits would seem to fit.

Taking a theoretical on-target burst with a 90% chance of leathality, for the following set up's you'd need the following firing times

2 x Hispano II (~650 rpm): 1.33 seconds
2 x Hispano V (~750 rpm): 1.16 seconds
4 x Hispano V (~750 rpm): 0.58 seconds
6 x M2 (~800 rpm): 1.25 seconds
8 x M2 (~800 rpm): .94 seconds
4 x .303 Browning (~1150 rpm) 1.36 seconds
8 x .303 Browning (~1150 rpm): 0.68 seconds
12 x .303 Browning (~1150 rpm): 0.45 seconds

That makes the .303 appear obscenely good. And also the mixed .303/20 mm battery. Unfortuantely, it doesn't include things like dissimilar ballistics and gun positioning.

 

[Shortround6]

It also doesn't take into account different ammo types.

British were using 4 different types of projectiles in the .303 during the Bob.

The Americans had .50 cal ball, AP, tracer and incendiary up until 1943 when they began to introduce the M-8 API. By some point in 1944 most fighters were using almost 100% M-8 API. M 23 incendiary was coming in at the end of the war I believe?

Not only do the Hispano rounds vary but even on the same type shell (HE) the fuses were changed at times.

The trial results are a nice find but they represent a snapshot in time of the weapons capability at the time of the trial/test.

 

[CobberKane]

I'd suggest the .303s might be getting a break because the test was conducted at comparatively short range (200 yards.) The destructive power of the 303 rounds could be expected to drop off more rapidly than that of the .50 or 20mm. As aircraft speed increased throughput the war so did typical ranges, which would have further worked against the 303. This might account for the apparent effectiveness of the 303 in this test compared to the combat experience of pilots, who generally considered it inadequate as sole armament.

 

[Glider]

On the Williams web site it gives the time taken to match the firepower of the Me 262 for one second.

For the
6 x 0,5 it takes 6.5 seconds
8 x 0.5 - 4.8 seconds
8 x LMG - 14.5 seconds
4 x 20mm Hispano II 2.9 seconds
4 x 20mm Hispano V 2.3 seconds
Jap 4 x type 99-2 4.8 seconds

It seems to be broadly inline with the above comments. What is interesting is that he allows for the effect of Sync on the aircraft when comparing aircraft with different weapons. So a

190 A8 takes 2.8 seconds
La 7 - 7 seconds
Spit 2 x 20mm and 4 x LMG - 4.8 seconds
Spit 2 x 20mm and 2 x HMG - 4.5 seconds
109 F 1 x 20mm and 2 x LMG - 10.3 seconds
P38 5.3 seconds

It does show how the 20mm made a significant difference to the firepower of the aircraft. Also that USAAf fighters had at best average firepower for the war in 1944/5 but that was sufficient for the targets they were shooting at

 

[Jabberwocky]

I'd suggest the .303s might be getting a break because the test was conducted at comparatively short range (200 yards.) The destructive power of the 303 rounds could be expected to drop off more rapidly than that of the .50 or 20mm. As aircraft speed increased throughput the war so did typical ranges, which would have further worked against the 303. This might account for the apparent effectiveness of the 303 in this test compared to the combat experience of pilots, who generally considered it inadequate as sole armament.

I think you're onto the right path.

The tests and analysis I've seen suggests that the 12.7 x 99 round was somewhere between 1.9 times and 4.1 times as effective as a light machine gun round like the .30, .303, 7.92, 7.62 Soviet.

Most LMGs were probably only about 1/4th to 1/3rd as effective as the big Browning, but some guns made up the difference with very high RoFs. The US and UK Browning had RoFs of about 1150-1350 rpm, the MAC 1934 had a RoF of about 1400-1500 rpm and the ShKAS had a RoF of about 1800 rpm.

Where the LMGs also make up ground on the Browning is their weight (ranging from 7.5 kg to around 12 kg, compared to the M2's weight of about 29 kg). This means that while the M2 was very effective, it wasn't very efficient.

Thinking about it, I believe that's where a lot of the argument about the M2 vs the 20 mm is coming from.

The M2 Browning was a big, heavy weapon, firing a big heavy round at a high velocity at a reasonable rate of fire. That means that while in terms of damage to targets, it was effective, it was also not very efficient. Lots of firepower, not that much efficiency.

The Hispano was also a big heavy weapon, firing a big heavy round at a high velocity at a moderate rate of fire. However, in terms of firepower per weapon, it was much more efficient that the M2. More firepower, but also more efficency.


In terms of gun efficency, the M2 is about middle to bottom third when it comes comparing WW2 aircraft basic gun 'efficency' measures like muzzle energy vs installed gun weight, or throw weight vs gun weight or ammunition power vs gun weight.

That means that while both the M2 and the Hispano were effective at destroying targets, the M2 was less efficient, in the fact that US fighters had to carry around heavier batteries of weapons and larger amounts of ammunition that their contempories mounting cannon.

The installed weight of an M2 Browning and ancillaries was between about 70 and 75 lbs.
With 6 .50 cals and 275 rpg, total installed armament weight is about 830-860 lbs
With 8 .50 cals and 275 rpg, total installed armament weight is about 1105-1145 lbs

The installed weight of a Hispano II was about 147 lbs (and about 132 lbs for a Mk V)
With two cannon and 120 rpg, total installed armament weight is about 444 lbs.
With four cannon and 120 rpg, total installed armament weight is about 888 lbs.

If you agree that 1 Hispano was equal in firepower to somewhere around 2.5 to 3.5 M2s (and I do), then you could give all US fighters 2 x 20 mm Mk II with 120 rounds each (11-12 seconds firing time) and 2 x .50 cal with 275 rounds (20-21 seconds firing time) for about 585 lbs, installed weight.

This gives you roughly the same firepower as a P-47 for half the installed weight of its eight M2s or 70% of the installed weight of six .50 cals. So, you save somewhere around 520-550 lbs on a P-47, or 245-275 lbs on a six gun US fighter.

How much acceleration, rate of climb, rate of turn is that kind of weight shedding worth to a pilot in combat?

When they re-designed the P-51 to make the H model, the goal was to shave 600 lbs off the design. If the USAAF had armed it with two of the later Hispano Mk Vs and two M2s, then they'd have had a head start of nearly 275 lbs.

 

[GregP]

Regarding post #125, ins't that a YB-40?

Seems to have two turets on the belly.

 

[zjtins]

A P-47 with 8x.50 or 6x.50 Mustang was more efficient than a BF-109 with 1x20mm and 2 MG.

 

[zjtins]

I'd suggest the .303s might be getting a break because the test was conducted at comparatively short range (200 yards.) The destructive power of the 303 rounds could be expected to drop off more rapidly than that of the .50 or 20mm. As aircraft speed increased throughput the war so did typical ranges, which would have further worked against the 303. This might account for the apparent effectiveness of the 303 in this test compared to the combat experience of pilots, who generally considered it inadequate as sole armament.

I concur and that is one of the problems with test results combat results.

Extreme case is Germans wanting a 50mm or 75 mm round to take out a bomber in theory 1 round= 1 bomber much of the time. But the drawbacks for the implementation was not overcome in time.
That is my issue with the 20mm vs 50cal only looking at the round(s) and not the system.

 

[Shortround6]

A P-47 with 8x.50 or 6x.50 Mustang was more efficient than a BF-109 with 1x20mm and 2 MG.

I really do have to question if English is your first language.

Not meant as an insult but I am wondering if we have a translation problem.

There is little or no question that "8x.50 or 6x.50" is a more EFFECTIVE armament than 1x20mm and 2 MG.

Efficient brings in additional conditions or factors.

 

[Glider]

A P-47 with 8x.50 or 6x.50 Mustang was more efficient than a BF-109 with 1x20mm and 2 MG.

But you miss something. When the 109 with 1 x20 and 2 x Hmg was fighting the P51 normally had 4 x HMG so the firepower was in the 109 favour. Later the 109 were normally armed with 1 x 30mm and 2 x HMG, again the advantage was with the 109

 

[Jabberwocky]

A P-47 with 8x.50 or 6x.50 Mustang was more efficient than a BF-109 with 1x20mm and 2 MG.

I honestly can't tell if you're being serious.

The 1 x 20 mm and 2 x MG131 set up on the Me 109G5 onwards had about 70-80% of the firepower of the 6 M2s set up on the P-51, depending on which measure of firepower you want to use.

However, the Bf-109 has a much more efficient mounting, being centreline focused rather than spread across the wings. The mix 20mm/13.2 armament loses out a little with dissimilar ballistics, although not too much, as very few fighters were firing at targets beyond about 600m.

With 6 M2s and a total of 1880 rounds of ammunition, the P-51D's armament weight is just over 900 lbs.

With the MG151/20 and 200 rounds and the MG131 and 300 rounds per gun, armement weight is just over 300 lbs.

So, for one third of the P-51Ds armament weight and very similar trigger time (17 seconds for the MG151/20 and 20 seconds for the MGs), you get 70-75% of the firepower.

You could double the armament installation with the Bf-109 and still have less installed armament weight that the P-51D and a 40-50% advantage in firepower.

 

[CobberKane]

Leaving aside the specifics, its interesting to note that controlled analysis of data from controlled tests and conclusions drawn from real world experience often yield different results. Purely in terms of combat the 20mm outperforms the .50 comprehensively, but once we take into account the USAAF's established supply lines and the fact that American fighters were engaged overwhelmingly against other fighters, the case for converting to cannon is weakened. On the other hand the British started out using rifle caliber MGs against bombers and, results of the test conducted at 200 meters notwithstanding, the practical experience was that these were inadequate, lending impetus to the adoption of cannon.
The Germans ultimately tended towards the 30mm cannon as their best air to air weapon, and looking at the data for relative firepower and efficiency this would seem to be a no-brainer. But the Germans were concerned with knocking down large, tough bombers flying in straight lines; the firepower/efficiency numbers take no account of the difficulties of using such a slow firing, low velocity weapon against other fighters. Thus the 30mm would have made sense to the LW, but not the USAAF.
Purely in terms of firepower and efficiency the P-51H might have been better off equpiped with cannon or a cannon/HMG mix. But would the cannon fairings have created more drag than the extra firepower was worth, given the designers might never have envisaged their aircraft operating against tougher opposition than was already being encountered by the P-51D? And even if the short barrel 20mm as used in the Tempest V had been available, maybe the designers were already looking at the latter versions of the .50 with greatly improved ROF, as used in the Sabre.
The 303 looks surprisingly good in the tests, but aircraft were getting faster and typical ranges of engagement were increasing. Even in 1943 it must have been obvious that the next generation of fighters, and the jets to follow, would be firing on each other well beyond the ranges that the 303 would retain significant hitting power. Even the improved fifty cals of the Sabre were beginning to dull by the time of the Korean war.
The tests are interesting because they give us a basis to work from. Historically there is a general progression in primary air to air armament; from rifle caliber MGs to HMGs to cannon to guided rockets. Tactical considerations like logistics or the nature of the opposition might have delayed or influenced this progression, but at the end of the day the air forces concerned adapted what worked.

 

[zjtins]

But you miss something. When the 109 with 1 x20 and 2 x Hmg was fighting the P51 normally had 4 x HMG so the firepower was in the 109 favour. Later the 109 were normally armed with 1 x 30mm and 2 x HMG, again the advantage was with the 109

The P51 always had 6 not 4 MG. The Apache had 4x20mm.


Efficiency has a denominator, name your denominator so we can talk on equal terms.

 

[zjtins]

The MG131 was underpowered vs the Browning.
If you want pure efficiency then a.22 would look really good... but no on used it. For that matter the .30 probably look very efficient.

Efficiency is only one factor, it not effective then its moot.