Aircraft armament....

[Glider]

The US Navy in the Pacific felt that the 50 cal was quite effective aginst surface ships up to the size of and including DDs. There were instances of patrol craft and small coasters being disabled by AC armed with 50 cals.

I would certainly believe that wooden patrol boats and small coasters would be at risk but would be suprised if anything bigger would be at risk.

The USN were quite keen to introduce the 20mm, all F6-F5 Hellcats were capable of being equipped with 2 x 20 and 4 x 0.50.
Postwar I believe the USN were quick to introduce the 20mm whilst the USAAF stuck with the 0.50.

 

[renrich]

Actually, The plating of a DD was subject to being penetrated by the 50 cal especially with AP rounds and at fairly close ranges. Many of the gun mounts were open and the bridge structure was not armored to any extent. The older DDs, the sub chasers and minesweepers as well as small freighters were especially vulnerable. The reason the USN and belatedly the USAF went to the 20 mm was that a single hit from a 20 mm explosive shell was more likely to put an AC out of commission than a single 50 cal. The 50 cal relied on kinetic energy and penetration for it's disabling qualities. Statistically a given number of 20mm rounds would have a much better chance of fatally damaging an AC than would the same number of 50 cals. There is quite a lot of combat film showing Japanese shipping being strafed by AC with 50 cals. Of course one cannot see how much damage is being done. The 50 cal AP round would penetrate .75 inches of armor plate at 547 yards. I don't believe that the upper works or decks of any WW2 DDs had armor plate. The 50 cal AP round would easily penetrate an AC engine block or the side armor of a German half track or light armored car according to Wiki.

 

[Glider]

I don't disagree with what you say but knocking out some of the gunners and exposed crew would only rarely put a ship of any size out of action.
RAF Mossie and Beaufighters tasked with attacking escorts were well armed with cannons, machine guns and most importantly rockets. Even these were not expected to put the escorts out of action, just keep them quiet while the specialist torpedo/bomber aircraft went for the high value targets.

The rockets were the key weapon, most escorts lost to air attack (normally armed trawlers) were the result of attack by these weapons.

I am not aware of any vessel of any size being lost to HMG fire

 

[kool kitty89]

The .50 also had chemical energy in the API/I rounds. (the pure incendiary rounds being a simplified derivative of the British B.Mk.VI "De Wilde" bullet)
Which is important to remember with fire bing the big a/c killer. One major problem with the .50 in Korea was that with the less flamable Jet fuel (compared to gasoline) and the high altitudes often encountered, the API bullets often failed to ignite.

I think its worth remembering that when the decision was taken to arm the RAF fighters with 8 x LMGs, this was considered by all forces to be a pretty heavy armament.
The 109 of the same period had 3-4 x LMG, The Italians had 2 x HMG, The Japanese 2 x LMG, the USA often had 1 x HMG 1 x LMG, The French had 1 x 20mm and 2 x LMG.
Against this, 8 x LMG wasn't to be sniffed at.

Certainly in the late 30's, but by the stary of the war the newer cannon (albeit of modest performance) armmed Bf 109 was being introduced and the USAAC and USN were up armming their fighters. Export versions of the P-36 had 6x LMG with the P-40 being up armmed, not to mention the P-39 nearing service and P-38 in development. The USN had standardized on 4x .50's with their F4F-3 and the Brewster had been rather a pioneer with its 4x .50's (though one in the nose had previously been a .30, and the wing guns had originally been optional) Around the same time the A6M was on its way to entering service with it's (again modest performing) 20mm armament.

Its also worth remembering that before the war that the UK knew that the 303 wasn't a long term solution and that the 20mm Hispano was the way to go. The problem was of course, that the 20mm took longer than expected to be made reliable.

As for the HMG, I dont disagree that it was the best weapon for bomber defence and was sufficient for attacking other fighters and smaller bombers. However, if you had to go up against a 4 engined bomber then I believe it would have been lacking.

It would certainly have been better than the .303's though. And the .5 Vickers had been around since the 20's and, though passed up by the RAF, was in use on the ground and at sea in its water cooled form.

The Spitfire should have been able to carry at least 4, and proabably 6. (there would be only a slight gain in empty weight with 4x ~10 lbs, but ~60 lbs with 6x)

 

[Glider]

I will need time to dig it out but I am pretty sure that the vickers .5 was considered and took part in some trials in the mid 30s with other weapons but was rejected due to its weight and lack of performance.

 

[kool kitty89]

Yes, the RAF rejected it (along with the US .50 Browning) as I mentioned in post # 13:

Vickers was in the process of developing a scaled-up version of their .303" MG, chambered for a new .5" (12.7 mm) cartridge. This was produced in three versions for army, naval and aircraft use and was tested by the RAF in the mid-1920s against the new .50" Browning heavy machine gun, which was bigger and more powerful. The conclusion was that neither offered sufficient advantages to replace .303" MGs, since the slightly bigger hole they could punch wasn't adequate compensation for their greater size and weight and their lower rates of fire. The Swiss Oerlikon 20 mm cannon, developed from the German Becker of the Great War, was also tested in the late 1920s and early 30s and proved more promising since its explosive shells could do a lot more damage than just punching bigger holes, but it was big, heavy and slow-firing.

Tests of the 1921 version of the Browning and the contemporary Vickers .5" were found in favor of the Vickers. (though the M2 version was significatly improved)

In any case it would seem they overestimated the destructive power of the .303 compared to the .50 and overlooked the longer range and incendiary carrying ability. (weight for weight the incendiary capacity was about the same, but the larger rounds were significantly more likely to do damage)

It also seems to have been ignored that, despite significantly greater weight and lower rate of fire, it eventually becomes impractical to mount huge batteries of LMG in place of fewer HMG's of similar destructive power. They did manage to get up to 12x .303's in the Hurricane IIB (as well as the originally specified armament for the Typhoon and several others) but this takes a lot of space an would certainly not work in the Spitfire, while 6x .50 Vickers would fit much better, weigh a bit more, and have longer range. (and be much more powerful than the 8x .303 carried by the Spitfire, while still being able to fit, while more .303's woudn't)

While the 20 mm was obviously another step up the .50 would have been sort of an ensurance policy in case of developmental problems with the 20 mm, not to mention problems with mounting the much larger weapons.


In the '20s and early '30s the LMG's would generaly seem advantageous, but by the mid '30s it should have been clear that the progression of larger and stronger aircraft structures would leave the .303's lacking. (even without armor plate) At which time it was far from too late to adopt the .5" gun in addition to later adopting a 20mm weapon.



Even stranger, Rolls Royce was developing a Heavy aircraft machine gun (with emphesis on flexible/turret mountings) in the early 1940's, starting with a recoil operated version firing .50 BMG rounds, then gas operated gun in 1941, then a version using the .55 Boys ammunition. Work was abandoned in 1942. But why go through that trouble when you've got a decent HMG in the Vickers or just producing a modified version of the .50 Browning?

 

[slaterat]

Somewhere in one of my books I recall something being said that RAF testing showed that for the equivalent weight of guns .303s would do more damage to an aluminum airframe than .50 s. Its not too hard to imagine how one could draw this conclusion as 2 x 303s could put 2400 rpm into a target compared to only 650-700 for a single .50. The main limitation of the .303 or all rcmgs , as I see it, is that they are too easily defeated by light armour plate and self sealing tanks.

Kitty 89 wrote

In the '20s and early '30s the LMG's would generally seem advantageous, but by the mid '30s it should have been clear that the progression of larger and stronger aircraft structures would leave the .303's lacking. (even without armor plate) At which time it was far from too late to adopt the .5" gun in addition to later adopting a 20mm weapon

Keep in mind that the Air Ministry issued a spec for a 4 cannon armed fighter in 1936. In response Hawker proposed a 4 cannon Hurricane which was declined. Eventually the Hurri IIC did surface 5 years later.

Slaterat

 

[kool kitty89]

Yes and there were 4x cannon Spitfire V's, though not that common and the configuration was less than ideal. (too much recoil for the flexible wings of the early spitfires iirc)

As I said, the 20 mm was still in development at that time though, attempt of wing mounting the drum-fed Hispano went nowhere and the Mk.II wasn't available until after the BoB. The .5 Vickers could easily have been put into service as a suplemental gun, subsequently phasing out the .303 for aircraft.

Weight for weight, the .303 Browning is a bit more powerful, but, gun for gun the .50 was just over 2x as powerful and the Spitfire could have carried more than 1/2 the number of .50 guns than it could .303. (though the Hurricane could cary 12, albeit with the outer 4 spaced very far from the compact inboard 8 )

And round for round, comparing the "De Wilde" type incendiary .303 with the similar .5 vickers: the .303 weighs 9.8 g with .49 g incendiary content; the .5 Vickers round weighs 36.4 g with 1.94 g incendiary content. So roughly 4x the incendiary content along with longer range and better penetrating characteristics. (moderately higher velocity and significantly higher sectional density)

But, comparing the incendiary capacity alone (both had ~5% capacity, the vickers round weighed ~4x) it would take 10 .303 Brownings at 1,200 rpm (~100 lbs) to put the same weight of incendiary on target as 4x .5 Vickers at 750 rpm (at ~96 lbs). (note the 750 rpm figure was for the 1920's model, it may have improved by this time)

 

[kool kitty89]

For a propper destructiveness comparson (with Tony Williams' system) we need to compare the correct amunition with a similar mix as the one used on the .303 in Tony's table. (50% Incendiary with 50% of what apears to be ball)
For the .50 this would give an average ammo destructive power factor of 3.6 (compared to 1 for the .303)
At 750 rpm this gives a gun power factor of 45. (compared to 20 for the .303, and 60 for the .50 BMG)

 

[Glider]

Its an interesting debate but at the end of the day I still believe that the core of the problem for the RAF was the time it took to make the 20mm reliable. Had they done it on time its likely, indeed probable that the BOB would have been fought with 20mm armed Spits and Huricanes and most people who have praised the choice of the the 20mm.
They didn't, it was late and people have a tendancy to point out that the 0.5 HMG would have been a better choice.

Isn't hindsight a wonderful thing!!

 

[HoHun]

Hi Renrich,

>I would like to hear from those in the know how the recoil from the various weapons load would impact the fighter. I have a reference that mentions that in a F8F if the cannons on one side had a stoppage it really introduced a yaw component.

Even a single machine gun jamming is described as having this effect in the P-51 manual. The advice to the pilots was to fire only short bursts if that happened and not try to compensate for the yaw by use of the rudder, which would not yield the required accuracy for shooting successfully.

Regards,

Henning (HoHun)

 

[kool kitty89]

Its an interesting debate but at the end of the day I still believe that the core of the problem for the RAF was the time it took to make the 20mm reliable. Had they done it on time its likely, indeed probable that the BOB would have been fought with 20mm armed Spits and Huricanes and most people who have praised the choice of the the 20mm.
They didn't, it was late and people have a tendancy to point out that the 0.5 HMG would have been a better choice.

Isn't hindsight a wonderful thing!!

This is quite true, and compared to the problems with the reliability of the US produced Hispano, the development was very timely. Of course, the US was in a somewhat better situation with their .50 gun available.

That said the .50 in British service had other uses along side the 20 mm, basicly a replacement for all aplications still using the .303. (defensive armaments, suplemental armament to the 20 mm etc.)


It should also be noted that there were other choices for a decently performing cannon. Such that could enter service immediately in standard form and still have a fair margin of development potential which could be exploited in a shorter period of time than the Hispano was. (albeit without the potential of the later Hispano V)

Namely this one: ANOTHER MISSED OPPORTUNITY: THE OERLIKON FFL CANNON a weapon that had caught my interest for these qualities prior to finding this article. In its standard form it had significantly higher velocity (~750 m/s compared to ~600 for the FFF firing the same projectiles) with only a slight loss in RoF and moderate weight increase. (a good deal lighter than the Hispano -particularly the early versions- and a fair amount lighter than the High velocity -slower firing- FFS, while only slightly heavier than the .50 Browning)

Initially it would be drum fed (60 rounds like the FFF/ MG FF and the drum fed Hispano), but unlike the Hispano it could be easily mounted on its side in the wing. (with the drum next to it) Belt feed could then be introduced, and the Japanese demostrated that it could be sped up to ~750 rpm.

Also, due to the operating principal of the gun the recoil pulses were spread out in the firing cycle, resulting in less vibration, less stress on the airframe, and better stability while firing.


This weapon would also be suitable for flexible and turret mountings due to the compact size, weight, and good recoil qualities. (I immagine the drum feed would be preferred for flexible mountings)

 

[r2800doublewasp]

Well didn't the British usually have four .303 cal. machine guns on each turret (like on the B-24) instead of two fiftys

 

[kool kitty89]

In some cases yes, but in other turets there were only two and in flexible mountings only one. And 2x .50's would still be more effective than 4x .303's. (depending somewhat to which .50 gun you compare, but for the US gun by a good margin, also true for the Vickers, but less dramatically)

 

[KrazyKraut]

Which was the best aircraft fitted gun/cannon of WWII? And, why did the RAF stick with .303, what was their reasoning behind, why not go for bigger like .50's?

If you want one single answer it's either MG151/20 or Berezin B-20. They both performed very solid against anything they encountered. They both fit on almost any plane and in a variety of positions and they both are noted for their reliability. In the end the B-20 looks best on paper, but I don't know if its chemical energy component is as good as with the 151 and Minengeschoss. To be fair it only entered the war very late, so overall its MG151/20 for me.

 

[HoHun]

Hi Krazykraut,

>In the end the B-20 looks best on paper, but I don't know if its chemical energy component is as good as with the 151 and Minengeschoss.

Here is a comparison of the muzzle power of various WW2 weapons. You'll see that the B-20 comes out at about half the power of the MG 151/20 per barrel:

MK 213/30: 9.55 MW
MK 108: 5.03 MW
MK 103: 4.08 MW
NS-37: 2.17 MW
MG 151/20 (MX): 1.4 MW
MG 151/20: 1.27 MW
Hispano V: 1.23 MW
VYa-23: 1.2 MW
Hispano II: 1.06 MW
37mm M4: 0.91 MW
MG-FF: 0.78 MW
20mm Ho-5: 0.71 MW
20mm ShVAK: 0.64 MW
Berezin B-20: 0.64 MW
Ho-1 / Ho-2: 0.64 MW
20mm Type 99-2: 0.63 MW
20mm Type 99-1: 0.52 MW
MG 151: 0.44 MW
12.7mm UB: 0.37 MW
.50 Browning M2: 0.28 MW
MG 131: 0.21 MW
Ho-103: 0.18 MW
12.7mm Scotti: 0.14 MW
Breda-SAFAT: 0.14 MW
Browning .303: 0.09 MW
MG 17: 0.09 MW

Unfortunately I'm unable to make a proper comparison to the MG 151/20 battery vs. battery as I don't have the ammunition weight data for the B-20 (cartridge weight plus weight of belting). If anyone has reliable data on this (or maybe just the cartridge weight), that would allow a better comparison!

Regards,

Henning (HoHun)

 

[kool kitty89]

HoHun, those figures are for the kinetic energy figures only, without taking chemical content into account?

If you add chimical energy in it tends to skew things if you want to compare the merits of the guns. ([particularly if said guns were capable of using more destructive ammunition had it been available)

Also this tends to give an exageration of the destructive power, creating a much greater performance difference with increasing HE/I capacity than in Tony Williams' system. (which also uses momentum rather than energy)

Additionally the Ho-5 was capable of significantly better performance with the propper high strength alloys (used on early models), but lacking these the cartridges were significantly down-loaded dropping the ~830 m/s (for 112 g AP projectile) to only ~710 m/s.

 

[HoHun]

Hi Koolkitty,

>HoHun, those figures are for the kinetic energy (or momentum) figures only, without taking chemical content into account?

No, they are for total power, including chemical content.

Regards,

Henning (HoHun)

 

[vanir]

I'd like to add a document written by Sqn Ldr Ralph Sorley of Flying Operations 1 in the British Air Ministry.

"The choice lay between the 0.303" gun, the 0.50" gun and a new 20mm Hispano gun which was attracting the attention of the French, and in fact of other countries in Europe who could obtain knowledge of it from them. During 1934 this gun was experimental and details of its performance and characteristics were hard to establish. On the other hand, designs of better 0.303" guns than the Vickers had been tested over the preceding years with the result that the American Browning from the Colt Automatic Weapon Corporation appeared to offer the best possibilities from the point of view of rate of fire. Our own development of guns of this calibre had been thorough but slow, since we were in the throes of economizing, and considerable stocks of old Vickers guns still remained from the First War. The acceptance of a new gun in the numbers likely to be required was a heavy financial and manufacturing commitment. The 0.50" on the other hand had developed little, and although it possessed a better hitting power the rate of fire was slow and it was a heavy item, together with its ammunition, in respect of installed weight...the controversy was something of a nightmare during 1933-34. It was a choice on which the whole concept of the fighter would depend, but a trial staged on the ground with eight 0.303" was sufficiently convincing and satisfying to enable them to carry the day."

 

[vanir]

I'd have to hunt down the documentation, but I've also read the tremendous difference between MG FF types and MG151 both from pilot view and the receiving end.
Apparently the Oerlikon liked to tear large sections of airframe skinning away, but it had what pilots described as "sledgehammer recoil" (due to its origins not really being designed for aerial use), it felt like it was trying to tear the wings off when being fired, this seriously concerned many pilots. Mounted to fire through the engine vee, more recoil was absorbed by engine weight but it overheated and jammed frequently in this configuration.
By comparison the MG151/20 was an excellent gun with no complaints. On the receiving end it typically liked to punch small, fist sized holes through pretty much anything it hit: engine blocks, pilot armour, you name it.

From what I've read at Tony William's site the B-20 had a slightly higher rate of fire than the ShVAK and slightly better ballistics. The ShVAK is a very good weapon, either are probably as good as the MG151/20 on paper. I should look it up again, as it's been a while so I hope I recall this last, correctly and reflective of technical details. I'll get back to you with a link.