Why did US fighters not use cannon in WW2? [Archive]

Heathrow Harry

1st Mar 2018, 07:08

ian16th

1st Mar 2018, 07:51

Not an answer, but expanding the question.

The US carried on with this preference even with jet a/c such as the F-86. The F-86's 6 x 50 calibre machine compared to the Hawker Hunter 4 x 30mm Aden.

Fareastdriver

1st Mar 2018, 07:56

Having zero practical knowledge on this subject conjecture would suggest that a machine gun round has a higher muzzle velocity than a cannon shell so there is less deflection and more accuracy.

Sloppy Link

1st Mar 2018, 08:03

Is think it is down to effect, for the same weight penalty you can carry more guns/ammunition than the same in cannon along with the extra airframe bracing. Greater weight of fire, quantity has a quality all if it's own, cannon would put less rounds in the air but granted, probably only takes one to hit to have the effect.
Uneducated rationale

GeeRam

1st Mar 2018, 08:07

Heathrow Harry

1st Mar 2018, 08:17

yes - the idea that they had a pretty big industry set up anyway for 0.303 & 0.5 inch did strike me - far easier to ramp up production rather than go for something heavier

But carrying it into the jet age was rather bizarre............... especially when a Mig-15 carried 3 cannon................

Bing

1st Mar 2018, 08:36

From some reading I've done around the issue, they had the licence to make the same 20mm Hispano cannons as the UK but for some reason had massive quality control issues producing them. I believe the USN was at one point planning on standardising on the 20mm but due to the production issues went with the .50 cal instead.
I think the P-61 (?) Black Widow was armed with 20mm though as they'd just about sorted things out by that stage.

TorqueOfTheDevil

1st Mar 2018, 08:46

Leafing through some old William Green books I noticed that throughout the total production run of the main US WW2 fighters - P-47,Thunderbolt, P-51 Mustang, Wildcat, Hellcat all were only armed with machine guns . The Lightning carried machine guns and one cannon.

Only the later versions of the Corsair carried 4 cannon.

When you consider than in Europe cannon started to be fitted from 1939 across the fighter types of all nations this seems strange. Especially as the US was relatively quick to adopt self-sealing tanks, cockpit armour etc etc

Any idea why?

As others have noted, they decided (don't have the source material to hand) that for simplicity the standard armament for a fighter was 6x 0.5 inch guns. Don't forget the P-40 - more numerous than any of the naval fighters! This policy was varied slightly to suit specific airframes: the unusual layout of the P-38 and P-39 allowed space for a cannon as well as the machine guns, and the size of the P-47 allowed it to have two extra. Conversely, most of the F4Fs had to make do with 4.

The reasoning (IIRC) was exactly as Sloppy Link and Geeram have stated, and I suspect that the Americans felt vindicated when they saw the difficulties which other nations had at times with cannon-equipped fighters (the early Hispano-equipped Spitfires but also the German MK108). And even a typical mid-war Spitfire was pretty impotent against everything apart from a Zero once the 20mm ammunition had run out and all it had was 4x .303 guns.

Heathrow Harry

1st Mar 2018, 08:46

P-61 - 4 cannon plus 4 x 0.5 mg in the turret

Wikipedia on the Corsair

F4U-1C:

The prototype F4U-1C, appeared in August 1943 and was based on an F4U-1. A total of 200 of this variant were built from July to November 1944; all were based on the F4U-1D and were built in parallel with that variant.[82] (https://en.wikipedia.org/wiki/Vought_F4U_Corsair#cite_note-Russell_1984_p._28.-85) Intended for ground-attack as well as fighter missions, the F4U-1C was similar to the F4U-1D but its six machine guns were replaced by four 20 millimeter (0.79 in) AN/M2 cannons (https://en.wikipedia.org/wiki/Hispano-Suiza_HS.404) with 231 rounds of ammunition per gun.[127] (https://en.wikipedia.org/wiki/Vought_F4U_Corsair#cite_note-135) The F4U-1C was introduced to combat during 1945, most notably in the Okinawa campaign.

Aviators preferred the standard armament of six .50 in (12.7 mm) machine guns since they were already more than powerful enough to destroy most Japanese aircraft, and had more ammunition and a higher rate of fire.[128] (https://en.wikipedia.org/wiki/Vought_F4U_Corsair#cite_note-136) The weight of the Hispano cannon and their ammunition affected the flight performance, especially its agility, but the aircraft was found to be especially potent in the ground attack role."

All later Corsairs retained the cannon tho' I think

TBM-Legend

1st Mar 2018, 08:50

USAAF Beaufighter night fighters used 20mm and machine guns. P-39 used 37mm and 20mm cannons. On a Thunderbolt for example :Eight .50's with a total of 2400-3200 rounds had many advantages, and a few disadvantages, over four 20mm with 500-600 rounds. The .50 was a standardised weapon for logistics and had a much higher muzzle velocity than the then 20mm...remember E=mV2

DANbudgieman

1st Mar 2018, 08:51

The Mig 15 was designed from the outset to sweep the skies of the Soviet Union of any US A-bomb carrying aircraft. The suitability of the three cannon armament arrangement in this role was proven when the Migs forced the USAF to cease daytime operations over Korea with the B29.

The prime reason for the US retaining the .50 calibre well past its sell by date was cost. They retained huge numbers of this weapon and its associated ammunition in inventory after the end of the second world war. In the post war period they had no desire to fund starting production of a new weapon when they already held vast stocks of weapons already paid for

In terms of weight of fire, four 20mm cannon outguns six 50 calibre by a significant margin.

For the same reason the UK choose to arm the Hunter and Javelin with four 30mm Aden guns. This new generation was designed to protect the UK from A-bomb carrying Soviet jets. As it was considered that any defending aircraft may only have a fleeting opportunity for one burst of fire, a high volume of fire was of prime importance.

Just This Once...

1st Mar 2018, 08:53

I think the starting points were different for the US and UK. Here in the UK we had many aircraft fitted with light machine guns effectively firing a rifle bullet. The performance of this small calibre was marginal and we took a fresh look and migrated towards cannons.

The US started with a .50 cal HMG round which provided them with a superior capability from the outset. The US recognised the advantages of the cannon but the capability increase from the .50 cal was not as urgently needed compared to those who pitched-up to a war firing a bullet around a 1/4 of the weight and half the effective range of the .50 cal.

(NB some US aircraft had .30 cal weapons fitted and $ price comes into everything)

http://upload.wikimedia.org/wikipedia/commons/thumb/a/ab/Rifle_cartridge_comparison.jpg/250px-Rifle_cartridge_comparison.jpg

ORAC

1st Mar 2018, 09:26

And even a typical mid-war Spitfire was pretty impotent against everything apart from a Zero I believe this, along with the previous couple of posts, are most relevant.

It wasn’t a matter of what you were shooting from - it was what you were shooting at. In the Pacific War the vast majority of targets were unarmoured and the extant machine guns were more than adequate for the task and it would not have been logistically efficient to build another logistics chain and aircraft models for the European theatre.

Heathrow Harry

1st Mar 2018, 09:32

TBM - almost Beaufighters carried 4 cannon and 6x 0.303 -

Same reasoning as given by JTO - you might only hit the enemy with a few rounds and they had better do damage - W European military aircraft were generally better protected than either US or Japanese aircraft - certainly at the start of war .

Several US fighters imported into Europe early on showed substantial performance loss due tot eh need to fit armour, armoured glass and self sealing tanks....... the original P-51 being a case in point.........................

George K Lee

1st Mar 2018, 10:59

It seemed to me that a big factor was the prioritization of muzzle velocity (flat trajectory) and rate of fire, both of which would help compensate for less-than-excellent marksmanship. That carried over to the 1950s and the present day, with the quad-M-39 setup on the F-100 and F-8 and, of course, the M61.

Project Vulcan itself (I recall from history briefings) resulted from post-WW2 retrospective studies of gun lethality, which concluded that the average pilot was best served by something combining the characteristics of a rifle and a shotgun.

NutLoose

1st Mar 2018, 12:04

https://www.youtube.com/watch?v=eXh4Q5jwg78

Heathrow Harry

1st Mar 2018, 12:45

of course you can overdo the weight of shot - the 57mm, 6 pounder Mollins gun........

https://www.pprune.org/members/326184-heathrow-harry-albums-what-airfield-picture957-us57mm.jpg

https://www.pprune.org/members/326184-heathrow-harry-albums-what-airfield-picture956-tsetse.jpg

https://www.pprune.org/members/326184-heathrow-harry-albums-what-airfield-picture955-molinsa2.jpg

FakePilot

1st Mar 2018, 13:22

I would guess that the flatter trajectory and higher round count would allow for chancing shots in a dogfight and also allow fighters to sit outside the range of a bombers turrent.
Otherwise for cannon fighters the strategy sounded like "shoot when the enemy fills my windscreen"

Sometimes I consider the .50 BMG America's secret weapon of WWII.

Heathrow Harry

1st Mar 2018, 13:29

............... but one cannon hit did a hell of a lot more damage than a load of machine gun bullets

Just This Once...

1st Mar 2018, 13:37

Well, that sweeping statement needs a small 'it depends' addendum. Putting little incendiary .303 rounds into the unprotected fuel tanks of contemporary German light bombers didn't really leave a whole lot left. The argument only changed when the need to shoot further and harder became relevant.

KenV

1st Mar 2018, 14:03

So it really boils down to two major points:
1. Logistics/commonality. It was easy to mass produce large numbers of .50 BMG quickly, and provide lots of ammo for those guns which were common to lots of other vehicles, to include a dozen or more on every B-17 and B-24 bomber, plus the numerous guns on B-20, B-25, B-26, etc etc., And it was easy to get all those guns and all that ammo from the USA to the far end of the Atlantic and the Pacific. This was essentially the same reason that US tanks used gasoline engines rather than diesel. Despite the far greater fire danger posed by gasoline, it simplified logistics by having a single type of fuel for everything from light jeeps to heavy tanks.
2. Good enough. The targets being shot at were light enough that a .50 BMG did the job. Neither the Germans nor the Japanese had large bombers that needed to be shot down. The exceptions of cannons on US aircraft was for air to ground use, not air to air. And even then, large numbers of .50 BMG rounds on a truck or other ground vehicle (even armored ones) were effective at disabling them even if they did not destroy them. And often disabling was all that was needed. So the crew flying them usually preferred the machine gun equipped aircraft over the cannon equipped aircraft.

There is a third lesser point. Both the AN/M2 (the lightweight aviation version of the ubiquitous "Ma Deuce") and its ammo was relatively small and compared to cannon, very light. Both are very important considerations in a fighter.

izod tester

1st Mar 2018, 15:02

I recall reading that Capt Eric "Winkle" Brown shot down 2 FW 200 Condor whilst flying the Grumman Martlett (Wildcat) from HMS Audacity. Thus the .50 cal ammunition was effective against a large 4 engined aircraft. Although the Sea Hurricane with only 8 .303cal mg did manage to down 3 FW 200 Condors, there were a number of occasions when they were unable to inflict sufficient damage to shoot them down.

Heathrow Harry

1st Mar 2018, 15:24

The FW 200 was a minimally altered airliner that had serious issues with both fuselage and wing strength - the literature is full of pictures of them falling apart (literally) on landing or taxying. So not the worlds toughest target

IIRC two of the toughest were flying boats - the Sunderland and the Kawanisi 8K "Emily" could take an outstanding amount of punishment apparently

Onceapilot

1st Mar 2018, 15:49

Ken. WW2, most German and British tanks also used gasoline.
As far as fighter use of Cannon goes, the Germans had quite a lead in the availability and the installation of cannon type weapons. They seem to have appreciated the advantages of the larger calibre well before the RAF and had the 20mm weapons in the wings of the Bf109E before WW2, having learned the lessons in Spain. The RAF seemed to agonise about cannon and the Spitfire had to wait till Nov '40 for the Mk1b to get 20mm cannon in the wings working satisfactorily, while the Luftwaffe outgunned them through the BoB. By the time of the Spit Vb, the Germans had sorted the engine mounted cannon in the 109F and, shortly after, the Fw190 with at least two wing root mounted 20mm, sometimes four and, nothing below 12.7mm. The Germans preferred the bigger weapons and soon moved on to the 30mm MK108. This weapon suffered from early poor quality but did become reliable enough and, with the thincase "minen" type blast shells they were a very effective weapon, only an average of 4 hits req'd to down a heavy bomber. For the Americans, it would seem that the .5 BMG was sufficient to deal with many situations, particularly against fighters and small bombers. Certainly, there was an element of strength in numbers, with 6x .5BMG and generally huge numbers of P51's hunting the Jagdwaffe in the later stages of the War. However, the pure effective weight of fire from the 4xMK108 in a 262 was impressive. Interestingly, the late developed MG213 20mm and MK213 30mm revolver cannon were the basis of many postwar weapons, including the ADEN 30mm and latterly, the Mauser 27mm in the Tornado. Of course, the Americans developed some excellent revolving barrel weapons. However, the instantaneous rate of fire achieved by the revolver type Mauser can be an advantage in a .5sec snap burst and, the installed weight of the Mauser is low.

OAP

SASless

1st Mar 2018, 15:50

Six or Eight .50 Caliber machine-guns focused at a point some several hundred yards in front of the aircraft put a lot of Rounds in a very small area.

There is no comparison between a .50 caliber round and a .30 caliber for effect.

The Spit with four 20MM cannon must have been a distinct improvement over the .303 equipped versions.

Onceapilot

1st Mar 2018, 15:54

rolling20

1st Mar 2018, 19:02

The RAF seemed to agonise about cannon and the Spitfire had to wait for the MkVb to get 20mm cannon in the wings,

OAP
Not quite correct I am afraid. 19 Squadron had Spitfire Mk1bs with cannon in May/June 1940, but suffered from problems with their operation. I remember reading somewhere years ago that a pilot fired on a ME 109 ( and I am sure this was over Dunkirk) and immediately the windscreen of his Spit turned red!
There was also a Hurricane at North Weald called the 'old cow' (IIRC) with 20mm cannon ,that was somewhat slower @300mph than the Browning armed ones. It has been suggested by numerous BoB pilots, that had cannon fighters been more available, the outcome would have been even more decisive.

Onceapilot

1st Mar 2018, 19:45

Not quite correct I am afraid. 19 Squadron had Spitfire Mk1bs with cannon in May/June 1940, but suffered from problems with their operation. I remember reading somewhere years ago that a pilot fired on a ME 109 ( and I am sure this was over Dunkirk) and immediately the windscreen of his Spit turned red!
There was also a Hurricane at North Weald called the 'old cow' (IIRC) with 20mm cannon ,that was somewhat slower @300mph than the Browning armed ones. It has been suggested by numerous BoB pilots, that had cannon fighters been more available, the outcome would have been even more decisive.

Thanks rolling. I have corrected my post. The Spit Mk1bs issued to 19 Sqn were withdrawn because of constant weapon failures. The cannon installation in the 1b only became acceptable by Nov '40, after the BoB.

OAP

typerated

1st Mar 2018, 19:51

rolling20

1st Mar 2018, 20:15

Thanks rolling. I have corrected my post. The Spit Mk1bs issued to 19 Sqn were withdrawn because of constant weapon failures. The cannon installation in the 1b only became acceptable by Nov '40, after the BoB.

OAP
Pleasure OAP, thank you.

rolling20

1st Mar 2018, 20:29

I think this is the wrong way round:

Rather than the USAAF to cannon, the RAF should have gone for 0.50 cal.

We all know the 0.303 is too light and 20mm too slow and low rate of fire for A2A.
Carrying both didn't make up for the deficiencies of the other!
The thinking at the time was one of accuracy. The powers that be weren't that confident of a pilots ability to hit a target and a spread of .303s offered the best chance of hitting a target.
Cannon were thought about pre WW2, but ditched for .303. The 8 gun fighter was a potent weapon when thought of in the mid 30s. The idea was even toyed with 10 or 12 guns. I believe tests were carried out pre war on .5s, but the results were disappointing.

Onceapilot

1st Mar 2018, 20:38

Interestingly, reading about the Hispano-Suiza 20mm cannon development, it seems that the weapon development in the USA was never satisfactory during wartime and so, the continued use of the .5 Browning was something of a force-majeure.

OAP

tonytales

1st Mar 2018, 22:31

I think it was recognized that they needed something bigger than the 0.50 cal HMG. The USN held a "Joint Fighter Convention" in 1944 and the moderator told the attending aircraft companies that they should provide room in their designs for the oncoming T17E3 .60 cal Aircraft MG. It was pretty impressive gun, had a very high muzzle velocity but never made it to use. Some large production contracts were canceled.
This link will provide you with more than you probably want to know about the T17E3 .60 Cal MG. Just scroll down on the posts.
https://www.milsurps.com/showthread.php?t=32509

DODGYOLDFART

1st Mar 2018, 23:01

The simple fact of life of cannon v machinegun is quite simply that the increased size of the cannon round allows the incorporation of high explosive charges, complex fuses and incendiary components. Late in the WWII the RAF carried out extensive evaluations of the effectiveness of many different calibres and types of ammunition. The result was that the 20mm Hispano semi-amour piercing incendiary round was by far the most effective round in aerial combat. It was also very good when used for strafing and was quite capable of penetrating the upper armour of the Panzer Mk4.

Subsequently in the Korean war it was established that .5" Browning ammo. used by the F86 Sabre was being deflected by the airflow over the wings and fuselage of the Mig 15 once speeds got up to round Mach .85. It was established that this was largely due to the light weight of the .5 cal. bullets.

tdracer

2nd Mar 2018, 02:12

As others have noted, the US fighters didn't often face heavy bombers in either the European or Pacific Theaters, and the 50 cal. did the job quite well on the smaller aircraft (especially the Japanese which lacked defensive armor and such).
My dad fought in the South Pacific - Guadalcanal, New Guinea, Philippines. By the time he got to Guadalcanal in late 1942 the P-39 was pretty much outclassed for air-to-air, but was very effective for air to ground with that big cannon in the nose (TBM - I thought all the P-39s had 37mm cannon but perhaps some used the 20mm). According to my dad, when the P-39 fired that 37mm cannon during a strafing run, he could see the aircraft 'stutter' from the recoil. If his observation was correct, I can't help but think that firing that big cannon during a dog fight would make aircraft control very tricky. Further, for air-to-air, mixing (relatively) slow cannon with higher speed 50 cal. would make leading the target for both nearly impossible.
The picture that Just This Once posted helps, but it is hard to appreciate how big a 50 cal round really is if you haven't seen one. I have a bottle opener made out of an inert 50 cal round and it is HUGE!

megan

2nd Mar 2018, 04:45

One analysis.

WORLD WAR 2 FIGHTER GUN EFFECTIVENESS (http://www.quarryhs.co.uk/WW2guneffect.htm)

TBM-Legend

2nd Mar 2018, 05:56

but perhaps some used the 20mm

P-39D-1 and P-400 [ex-RAF ordered Airacobras] used the 20mm cannon...

Heathrow Harry

2nd Mar 2018, 06:23

Megan

Thanks for that link - it really covers all the bases!!

Onceapilot

2nd Mar 2018, 07:24

Further, for air-to-air, mixing (relatively) slow cannon with higher speed 50 cal. would make leading the target for both nearly impossible.
!

Many of the fighters had the different weapons boresighted to give a concentration of the different trajectory weapons at a certain range. This gave a reasonable sighting solution. Also, many of the cannon were giving high rates of fire that allowed their mixed use (most notably by German piston fighters) simply as a combined weapon. The use of very large slow firing guns was different, and they would usually be used to take individual aimed shots.
Cheers

OAP

TorqueOfTheDevil

2nd Mar 2018, 09:19

I recall reading that Capt Eric "Winkle" Brown shot down 2 FW 200 Condor whilst flying the Grumman Martlett (Wildcat) from HMS Audacity. Thus the .50 cal ammunition was effective against a large 4 engined aircraft.

Well it could be, in the right hands: there are also accounts of Ki-43s downing American heavies (from memory, early model B-17s ie without turrets) with the absurd armament (for 1941-2) of 2x 7.7mm guns! The quality of the IJAAF pilots early in the war made up for the apparent deficiencies - not just armament - of their mounts. Even the later Oscars had 1x 7.7mm gun and 1x 12.7mm...

The idea was even toyed with 10 or 12 guns.

The Hurricane IIB entered squadron service with 12x .303s I think? Although the IIC and IID appear to have been more successful, albeit mainly air to ground.

rolling20

2nd Mar 2018, 09:43

The Hurricane IIB entered squadron service with 12x .303s I think? Although the IIC and IID appear to have been more successful, albeit mainly air to ground.
IIRC they were originally MKll A Series 2 , when they first were introduced? They became the IIB shortly after.

TURIN

2nd Mar 2018, 11:16

For clarity could someone define the difference between 'Cannon' and 'Machine Gun' please?

Thanks.

Just This Once...

2nd Mar 2018, 11:38

There isn't a universally accepted definition but we (RAF that is) tend to regard anything above 14.7mm as a cannon but other factors are considered too. Cannon projectiles are typically large enough to accept an HE charge (amongst other options) and usually fired via an electric impulse (rather than striker fired) and typically employ either a rotating breach or barrel (rather than a simple reciprocating mechanism).

For aircraft the 'cannon' term is an abridged form of auto cannon or rotary cannon, but most aircrew just call it a gun.

Green Flash

2nd Mar 2018, 11:43

I was once told that a machine gun could be carried and fired from a standing position by a human being type person, a cannon would need a mount of some sort.

TorqueOfTheDevil

2nd Mar 2018, 13:18

I was once told that a machine gun could be carried and fired from a standing position by a human being type person, a cannon would need a mount of some sort.

Did you ever put this theory to the test?!

thing

2nd Mar 2018, 15:26

I asked a wartime Spit pilot why you never saw the Mk IX in four cannon fit. They had the fitting for four cannon but only carried two. Apparently the wing flexed so much when firing four cannon that aiming became pretty much useless.

As has been noted, the early F4 carried only four 50 cal guns. There was some opposition from pilots when they released the six gun wing as the ammunition carried for each gun was less, and as the pilots figured, if you can't hit a target with four guns you're not going to hit it with six.

Onceapilot

2nd Mar 2018, 16:37

For clarity could someone define the difference between 'Cannon' and 'Machine Gun' please?

Thanks.

WW2 German aircraft weapon designations seem to have a clear demarcation of machine gun -up to 20mm and, machine kannone for 30mm weapons. Cheers

OAP

Argonautical

2nd Mar 2018, 17:17

I recently read "MIG Menace Over Korea" by Nicolai Sutiagin (22 kills) and he was quite derogatory about the F-86's armament. He said they often found strikes on their Migs where the .5 bullets had bounced off.

tonytales

2nd Mar 2018, 21:09

The F-86 armament of 6 x .50 cal MG was not effective. The US Navy instead incorporated 4 x 20 mm cannon into it FJ-2 Fury II proving the airframe could accommodate them. Unfortunately they were too late to take part in the Korean War and thus prove the superiority of the 20 mm cannon against the .50 cal mg.

megan

3rd Mar 2018, 03:21

Several US fighters imported into Europe early on showed substantial performance loss due tot eh need to fit armour, armoured glass and self sealing tanks....... the original P-51 being a case in point.........What tends to be forgotten is that the P-51 started life as a British aircraft, albeit designed and produced in the USA. It was built to specifications laid down by the British. No modification was necessary upon arrival in the UK. The P-51 came with all the items you list Harry. Windscreen was 1.5 inch armour glass,the pilots seat had a 5/16 inch plate from just below the seat to a point level with his shoulders and a 7/16 inch plate above this to protect the head, a 3/8 inch thick firewall, armour plate forward of the coolant tank, and self sealing fuel tanks. You can see the British bought their combat experience to the design.

Early versions of the P-51 had four 20mm cannon, a report written on 30 December 1942 recommended changing from the 20mm to .5 inch because,The present armament is considered adequate, but is functionally unsatisfactory. It is believed that four .50 cal (high rate fire) guns would furnish ideal firepower. It doesn't spell it out, but infers to me that stoppages were a problem.

Heathrow Harry

3rd Mar 2018, 07:07

Indeed - tho to be pedantic the British ones were NA-73's and NA-83's and because we'd spec'd them they came with most of the necessary kit -and adding the "Merlin" later made it the best fighter of WW2

Somewhat off topic but reading around I never realised that the P-47 bubble canopy was adopted after they tested it with a Typhoon canopy.. I think the P-51 canopy was a US improvement over the UK part bubble canopy adopted from the Spitfire

DODGYOLDFART

3rd Mar 2018, 10:00

What tends to be forgotten is that the P-51 started life as a British aircraft, albeit designed and produced in the USA. It was built to specifications laid down by the British. No modification was necessary upon arrival in the UK. The P-51 came with all the items you list Harry. Windscreen was 1.5 inch armour glass,the pilots seat had a 5/16 inch plate from just below the seat to a point level with his shoulders and a 7/16 inch plate above this to protect the head, a 3/8 inch thick firewall, armour plate forward of the coolant tank, and self sealing fuel tanks. You can see the British bought their combat experience to the design.

Early versions of the P-51 had four 20mm cannon, a report written on 30 December 1942 recommended changing from the 20mm to .5 inch because,It doesn't spell it out, but infers to me that stoppages were a problem.

Stoppages always were a problem with early wing mounted Hispanos and continued to be a problem until the later Martin Baker belt feed mechanism came into use. The Westland Whirlwind which came into service around the time of the Battle of Britain had four nose mounted Hispanos and suffered with far fewer stoppages. This led to the belief that the cause of stoppages in the early Spitfires was due to the wings flexing. This may or may not have been a contributing factor as the later Hurricanes which had a stiffer wing had fewer stoppages than the Spits. However probably the most likely cause was firing while pulling more than about to two "G" which was inevitable with most deflection shooting. This problem remained with the Meteor night fighters right up until they were withdrawn in the early 1960's even though they had MB belt feed mechanisms.

TURIN

3rd Mar 2018, 10:08

WW2 German aircraft weapon designations seem to have a clear demarcation of machine gun -up to 20mm and, machine kannone for 30mm weapons. Cheers

OAP

Thank you. I get confused when people use .50 Cal and 30mm etc

FODPlod

3rd Mar 2018, 11:33

In modern parlance, surely a cannon fires explosive-filled rounds while a machine gun fires solid projectiles, including tracer rounds?

Load Toad

3rd Mar 2018, 15:01

I recall reading that Capt Eric "Winkle" Brown shot down 2 FW 200 Condor whilst flying the Grumman Martlett (Wildcat) from HMS Audacity. Thus the .50 cal ammunition was effective against a large 4 engined aircraft. Although the Sea Hurricane with only 8 .303cal mg did manage to down 3 FW 200 Condors, there were a number of occasions when they were unable to inflict sufficient damage to shoot them down.

IIRC he chose to attack from head on to avoid the 20mm defensive armament - and shoot into the cockpit...

Load Toad

3rd Mar 2018, 15:07

I think this is the wrong way round:

Rather than the USAAF to cannon, the RAF should have gone for 0.50 cal.

We all know the 0.303 is too light and 20mm too slow and low rate of fire for A2A.
Carrying both didn't make up for the deficiencies of the other!

Well, they won so something went right....

the Move to 20mm Hispano and ultimately 4x of such...

Load Toad

3rd Mar 2018, 15:13

In modern parlance, surely a cannon fires explosive-filled rounds while a machine gun fires solid projectiles, including tracer rounds?

No - that's not the definition of cannon. Its about the caliber.

Carbon Bootprint

3rd Mar 2018, 17:14

I'm going to step out on a limb here and probably get flamed, but when you say "stoppage" I infer that to mean that the weapon was prone to jamming, and that the term has nothing to do with its actual effectiveness in "stopping" an enemy aircraft. Is that correct?

Sorry, but British is not my first language. :O

rolling20

3rd Mar 2018, 17:40

rolling20

3rd Mar 2018, 17:58

Stoppages always were a problem with early wing mounted Hispanos.... This led to the belief that the cause of stoppages in the early Spitfires was due to the wings flexing. This may or may not have been a contributing factor as the later Hurricanes which had a stiffer wing had fewer stoppages than the Spits.. The problem with the early cannon Spitfires was that the cannons were laid on their sides (rather than their belly) and were drum rather than belt fed. The reason they were laid on their sides was due to the shape of the Spitfire wing. Stoppages were an early problem. These issues weren't ironed out until autumn 1940. The early 8 gun, then 4 machine gun /2 cannon and later 4-8 machine gun and 2-4 cannon Spitfires, all had different wings.

tdracer

3rd Mar 2018, 20:58

No - that's not the definition of cannon. Its about the caliber.

Classic example is that massive cannon on the A-10. It's designed to fire solid projectiles at extreme velocity (and extreme rate of fire) with the ability to penetrate heavy armor.
I suppose it would be possible to use an explosive round in the A-10 cannon but if it's ever been tried or even proposed I've not heard of it.

Argonautical

3rd Mar 2018, 21:24

Not quite correct, the A-10's gun also fires a high-explosive round - the PGU-13/b High Explosive Incendiary (HEI) cartridge. The 14/b round is API with a depleted uranium core.

megan

4th Mar 2018, 00:50

I never realised that the P-47 bubble canopy was adopted after they tested it with a Typhoon canopyWas the British who developed the techniques necessary to mould a teardrop canopy.

Heathrow Harry

4th Mar 2018, 07:38

TBH I believe that was the case with the F-51 and the initial P-47 test but that the 'Mericans came up with an easier to build model for the P-47

tdracer

5th Mar 2018, 01:20

Not quite correct, the A-10's gun also fires a high-explosive round - the PGU-13/b High Explosive Incendiary (HEI) cartridge. The 14/b round is API with a depleted uranium core.

Interesting - has the HEI ammo ever been used in combat? Serious question (not yanking your chain), I'm curious - because everything you ever see or hear about the A-10 is tank busting with those API rounds.
I recall seeing an interview with an A-10 pilot who got an air-to-air kill when he came across an Iraqi helicopter (I'm thinking the First Gulf War, but I could be wrong). Anyway he said something like 'I gave it a five second burst and there wasn't much left...'.

SnowFella

5th Mar 2018, 03:38

Think most current usage has been the HEI ammo, API isn't really that well suited against unarmored targets...and not many targets while running air to ground in Afghanistan is armored.

Load Toad

5th Mar 2018, 05:09

Classic example is that massive cannon on the A-10. It's designed to fire solid projectiles at extreme velocity (and extreme rate of fire) with the ability to penetrate heavy armor.
I suppose it would be possible to use an explosive round in the A-10 cannon but if it's ever been tried or even proposed I've not heard of it.

There's an HEI round - PGU-13/B

https://www.prnewswire.com/news-releases/general-dynamics-awarded-33-million-for-30mm-pgu-13-cartridges-120058399.html

https://www.gd-ots.com/munitions/medium-caliber-ammunition/30mm-gau-8a/

KenV

5th Mar 2018, 15:55

.The early 8 gun, then 4 machine gun /2 cannon and later 4-8 machine gun and 2-4 cannon Spitfires, all had different wings.All those different wings cannot be good for mass production, nor for logistics/maintenance. And that was one big reason why the US pretty much standardized on machine gun armament. It greatly simplified production as well as logistics.

Argonautical

5th Mar 2018, 16:18

tdtracer said "Interesting - has the HEI ammo ever been used in combat?"

The Dutch ship protection GoalKeeper CIWS system uses the same gun as the A-10's. I should imagine the standard round would be the HEI ammo and it has been used in combat against Somali pirates.

Bing

5th Mar 2018, 19:14

All those different wings cannot be good for mass production, nor for logistics/maintenance. And that was one big reason why the US pretty much standardized on machine gun armament. It greatly simplified production as well as logistics.

It's not as bad as it sounds, by late '41 early '42 the Spitfire Vc was introduced with the universal wing that could carry any of those combination of weapons. Bear in mind there were other modifications being made to the wing as the aircraft evolved to strengthen it and ease production so it's not as if a wing from a Mk1 would have worked on a Mk9 anyway.

http://spitfiresite.com/2010/04/concise-guide-to-spitfire-wing-types.html/2

Heathrow Harry

5th Mar 2018, 19:19

"All those different wings cannot be good for mass production"

true but they were evolving rapidly to meet a whole bunch of different threats - from 1938 - 1943 things moved on a very long way

cargosales

6th Mar 2018, 03:34

Think most current usage has been the HEI ammo, API isn't really that well suited against unarmored targets...and not many targets while running air to ground in Afghanistan is armored.

And yet one of the most scary / educating / informative experiences of my life was as a 16 yr old [err yes, MANY years ago] crossing a 1km wide plain, along with the other 150 lads on that ex .... when 3 x A-10s turned up.

Whichever way we looked or faced there was always one threatening us, and another turning hard to engage. Our 7.62 rounds would probably just have bounced off anyway, had we even managed to hit it (because you were almost too busy looking for No.3 who was [panto time: Behind You!!)

Hmm, that told me a lot about numbers of a/c and how troops on the ground can or do react to one a/c or more than one a/c. And how many directions a person can look in at any one time..

CS

ian16th

6th Mar 2018, 08:43

Just found this: about fitting .50 cal Brownings to Spitfires. (http://spitfiresite.com/2010/04/sorting-out-the-e-american-armament-for-the-spitfire-mk-ixxvi.html)

An interesting paragraph:

It should be noted that compared with other aircraft weapons of the day, the performance of the Browning was rather undistinguished, especially in comparison with aircraft cannon widely used by other combating nations. The American gun was also very heavy. On the other hand, the USAAF had found it extremely reliable and simply “good enough” in air-to-air combat. This way the Browning became standard armament on American fighters – the P-51 Mustang, P-47 Thunderbolt or the F6F Hellcat, and more, with the same arrangement retained even for F-86 Sabre in post-war years.

FL235

6th Mar 2018, 10:47

Lots of good points raised here, but some interesting exceptions to the standardised 50 cal could be found. The mention of the P39 cannon doesn't convey what must have been a supply nightmare as some squadrons in the early days in New Guinea, equipped with a mixture of P39's & redirected p400's. That resulted in - 30 cal bmg in the wings, 50 cal in the nose, 20mm in the nose (p400) and 37mm in the p39. A logistics nightmare. And how about the modified field gun in the B25 (h?) On teh opposing side, The Zero packed a very interreesting licence-built 20mm Hispano that weighed much less than a 50 cal. I cleaned up one salvaged from a wreck in the sea and was impressed with its small size & light weight, part of the weight saving for the Zero. Low velocity, only 49 (I think ) rpg but very effective in the right hands, vide Saburo Sakai. Finding various often non-standard installations from both sides made for some interesting analyses.

longer ron

6th Mar 2018, 11:04

some squadrons in the early days in New Guinea, equipped with a mixture of P39's & redirected p400's. That resulted in - 30 cal bmg in the wings, 50 cal in the nose, 20mm in the nose (p400) and 37mm in the p39.

Ted Parks description of the P39/P400 cannon - because it was mounted in the prop shaft - he said...

The 37 mm went whump whump whump -When firing the cannon,your legs straddled it,the firing of it vibrated your prostate so the whole essence of war became mildly sexual.I do not know if this was intentional.
The 20mm version fired faster and went bababababababa and titillated you in a different way.Some men enjoyed it more.I was a 37mm man myself.

The P400 was also sometimes humorously referred to as a P39 with a Zero on its tail :)

the above quotes coming from one of Ted Parks books - either 'Nanette' or 'Angels Twenty' - cannot remember which - he flew P39/P400 ops in NG.

megan

7th Mar 2018, 00:56

The Zero packed a very interreesting licence-built 20mm HispanoJust mentioned for historical accuracy. The Zero used Type 99 Mark 1 cannon and Type 99 Mark 2 cannon which were Japanese versions of the Oerlikon FF and Oerlikon FFL.

SnowFella

7th Mar 2018, 06:13

And yet one of the most scary / educating / informative experiences of my life was as a 16 yr old [err yes, MANY years ago] crossing a 1km wide plain, along with the other 150 lads on that ex .... when 3 x A-10s turned up.

Whichever way we looked or faced there was always one threatening us, and another turning hard to engage. Our 7.62 rounds would probably just have bounced off anyway, had we even managed to hit it (because you were almost too busy looking for No.3 who was [panto time: Behind You!!)

Hmm, that told me a lot about numbers of a/c and how troops on the ground can or do react to one a/c or more than one a/c. And how many directions a person can look in at any one time..

CS

Mine came as the subject of 3 circling Apaches having been stopped by protesters near Srebrenik, BiH back in the late 90's.
Young and dumb (and firmly believing our "freedom of movement") I didn't take the hint of a long line of parked up cars and blew right past them just to get stopped a km further down the road by hundreds of peaceful protesters blocking off the road.
3 Swedes (2 logistics and our female chaplain) in one truck. No end of talking could get us trough but just as we were about to do a 59 point turn and head back a US convoy pulled up on our arse. :sad:
Lots more talking and hand waving took place and during that someone must of called it in and the Apaches appeared.

Eventually it took the better part of an hour to get the whole gaggle turned around and ending up with a detour back to Brčko, Čelić, Lopare and Tuzla to finally get us back on base.

Oh the memories!

rigpiggy

7th Mar 2018, 23:03

WORLD WAR 2 FIGHTER GUN EFFECTIVENESS (http://quarryhs.co.uk/WW2guneffect.htm)

a great treatise on the mg vs cannon debate

http://spitfiresite.com/2010/04/cannon-or-machine-gun-the-second-world-war-aircraft-gun-controversy.html

FL235

8th Mar 2018, 10:43

Thanks for the correction, Megan, I didn't have access to references at the time and the drum feed fooled me. Very impressed by the quality of steels and engineering, also the fact that it was, or appeared to be, a simple blow=back design firing from an open breech. On a different topic, and from somewhere earlier in the thread I noticed a quote from someone that an mg "should be able to be carried & fired by one man". I knew an armorer who tried the experiment, in Korea, of firing a .50 cal "from the hip", braced on sandbags, held down with all his weight. Luckily he only put three rounds in the links. First round somewhere near the target, second at 45 deg elevation, third vertically upwards, armorer flat on his back.

megan

9th Mar 2018, 04:14

Anyone with information as to the nature of the problems the US had in producing the Hispano 20mm. Would have thought mass production to the necessary tolerances would have been a given for the nation.

Edited to add: I think my question will find an answer here somewhere.

http://www.milsurps.com/content.php?r=347-The-Machine-Gun-%28by-George-M.-Chinn%29

TBM-Legend

9th Mar 2018, 05:46

My Mk 14 Spitfire had two 20mm Hispanos and two .5 Brownings fitted..

Heathrow Harry

9th Mar 2018, 07:01

Rather oddly the F8F Bearcat , which was to replace the F6F Hellcat, went back from 6x0.5 guns to only 4x0.5 guns

megan

10th Mar 2018, 01:16

The F8F Bearcat was designed as an interceptor where rate of climb was an overarching requirement, for weight saving armament was stipulated as 4 X .50 cal and ammunition load was reduced by 25% compared to the F6F, weight savings were also found in armour protection. Test pilots of the prototype requested installation of six guns, but never occurred, though the .50 cal were latter changed to 4 X 20mm cannons. The four .50 were deemed to be adequate against the lightly constructed opposition, who also lacked armour protection and self sealing tanks. Never saw combat, though a squadron was enroute to the zone when Japan surrendered.