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Hello: Just an off-the-wall question from a "colonial", who never tires of reading about/watching the amazing exploits of the RAF.
Why did so many, if not almost all British fighters/bombers in that war have guns with only .303 caliber guns, instead of the .50 as on many Yank planes? Was it mostly a matter of the weight of the ammo belts etc? Let's exclude the cannons on the stupendous Beaufighter etc.
Cos the yanks were late as usual and therefore had more time to fit bigger guns...
.303 (7.62mm ish) was the standard British army rifle and machinegun round so I think that is why it was selected initially. The standard fit for RAF single seat aircraft developed into 4 20mm cannon by the end of the battle of britain late 1940. This was based on the bitter experiance of german bombers wandering on despite being turned into sieves. It took some time to develop cannon for the wing mounts that were happy up to 30,000 feet and this was eventually solved with hot air feeds to prevent the breaches freezing. So in fact they were more heavily armed than the Mustang (4 x 12.7mm) tho i suppose was really british as well. It is debatable whether 4 x 20mm cannon firing an explosive shell was better than 8 x .5s(thunderbolt and others) firing non explosive shot.
Contempory german fighters, Bf109g (1943) had 1 30mm cannon in spinner and 2x 13mm machine guns. bf 110g (night fighter) 2x30mm 2x20mm rear gunner 2x7.9mm This had evolved following experience starting in spain in 1936 when the 109 had just 2 x 7.9mm machineguns.
British bombers , Lanc 2 twin .303 and 1 quad .303, American B-17 9 x .5 (12.7mm)
The later british bombers designed for night use where the gunners were really more use as lookouts. Indeed there is some debate as to whether they would have been better leaving the guns and turrets behind entirely and getting better height , though Bomber command would probably have just put more bombs on. The Americans had the knowlege of British use of the B-17 in daylight ops (disasterous) and decided to up gun it before they used it themselves.
So as you can see everyones ideas about aircraft armament developed through war experiance. Its just the Germans had a head start and the Americans gained a lot of British data.
I would guess that one reason was because, for many many years, the .303 round was standard issue to the British Military. Adaptation for use on RAF aircraft probably brought cost, logistic and supply advantages. (The bean counters again!)
Cannons were susequently fitted to a lot of RAF WWII fighters/bombers, to increase their hitting power.
1. .303 was standard calibre; the calculations about weight of fire leading to the decision that 8 guns were needed were based around this, IIRC.
2. Once .303 was proven to be a bit lacking (late 1940), ISTR reading that the plan was for fighters to have 20mm, with bombers getting .5. After Pearl Harbor, the Americans needed all the .5 they could get, which substantially delayed fitting weapons of this calibre to RAF aircraft.
My memory may well be flawed on both accounts, apart from the fact that .303 was the standard calibre (and appeared adequate at the time the aircraft were designed).
I have a friend who was a FAA pilot during the war. I've just asked him if he has any memories to contribute. His first thought was he didn't have a clue, but he's now had a chance to think about it, he's offered the following. Initially it was down to weight, the .303 being an overall lighter system. He also recollects "There is also the obduracy of the politicians on cost.....", so things don't appear to have changed much.
Re the British bomber armament. Air Chief Marshal Harris, C in C Bomber Command was asked by an Air Gunner why they were not given .5 machine guns instead of .303. Harris replied "how far can you see at night on ops", "about 300 yards" was the reply. "Exactly" says Harris "Whats the point of having greater range if you can not see the target". I cannot fault his logic and it confirms that the gunners were more useful as lookouts than engaging night fighters armed with cannon and machine guns in a gunfight.
That's interesting. Harris's official comments on the lack of a .5-inch are a bit different. He was responsible for getting the FN 82,. B-P 'D' (.5-in) and B.17 (20mm) turrets onto the stocks (as it were), but development was so slow that he recorded:
"Throughout, those responsible for turret design and production displayed an extraordinary disregard of the requirements of the command"
I can't help wondering whether the case above mightn't have been the AOC-in-C giving one of his men a plausible reason for why heavier calibre weapons weren't available. Even at close range, the .303 was lacking in 'Oomph' as opposed to the .5, and I'm pretty certain that I've read somewhere (Bomber Offensive? The Official History?) that he knew this and wanted action to deal with it.
I was also aware of 0.5 machine gunned turrets, I may be wrong but I thought that this was a local modification on 5 Group aircraft based in and around Lincolnshire. The modified turret was called a "Rose turret" after the engineers Rose of Gainsborough who were the engineers responsible. The RCAF 6 Group based in Yorkshire did something similar with a local modification of a single belly mounted machine gun as they suspected the existence of night fighters equipped with upward firing armament, in fact they were quite correct as the Luftwaffe had two upward firing cannon called Schragen Musik.
IIRC The lack of 50's had something to do with tests in ~1930 which resulted in the adoption of the Browning. The same tests showed no advantage of the 50 vs 303. This became doctrine and nobody really considered the a/c changes from fabric to metal skins with some armour.
When the problems with this approach became obvious in the late '30's there was worry about 50 proof armour so the decision was made to go straight for 20mm. Unfortunately the 20mm was not well developed and the prevvious applications were mostly engine mounted. This combined with general stress on engineering resouurces with rearmanent meant the development fell though the cracks until the need became critical. It didn't take too much time to fix the guns but a lot longer to arrange for 4x20 in the Spit wing.
The problem with the turreted 50's and 20mm was basically just the fact the turrets had to be redesigned, developed and debugged. This was a much bigger job and hence took longer.
After the war the pendulum went a bit far in bigger guns eg the 5 inch (4.5 ?/5.4?) recoiless automatic cannon. This chewed a lot of resources before it was realised the engine development wasn't going fast enough to deal with a weight of about a ton without ammo.
Those will have been the tests that led to the 8-gun interceptor concept - a Sqn Ldr whose name I forget calculated that in a modern engagement, no-one could be expected to track the target for more than seconds 2, and hence armament had to destroy HM Enemies within that time. He concluded that this required 8x 1000 rounds per minute machine guns. Brownings had just become available and fitted the bill.
They were originally either .3 or .5, but the British version was bored out to .303. No idea why, but the proposal that it was for commonality sounds sensible.
As to why the guns were modified to use .303, the following is given as a reason:
"The combination of severe economic problems and vast quantities of standard .303" weapons and ammunition in store after the First World War militated against the adoption of any new calibre. The 1930s rearmament programme therefore saw such weapons as the American Browning aircraft machine gun and the Czech ZB30 (better known in its British incarnation as the Bren Gun) expensively redesigned to fire the rimmed cartridge....."
Take the M11 Motorway from London and follow the signs to Stansted Airport. Duxford is on your left before you reach Stansted.
One point to bear in mind regarding the use of 303 calibre machine guns at the design stage of WW2 British aircraft is that 303 calibre was THE standard throughout the British Empire. That means not just the UK and the Dominions but India (including what is now Pakistan) Malaya & Burma, as well as the Colonies in Africa and the Middle East and those States under British protection elsewhere in the World. The introduction of a new calibre of weapon in peacetime had enormous implications throughout the entire Defence Establishment.
Incidentaly 20mm cannon were used by 19 Sqn during the Battle of Britain but were withdrawn due to teething problems with ammunition feed.
ISTT that most P-47s had eight .5 inch (although two guns were sometimes removed to save weight).
B-25 had up to 12 forward-firing (eight in solid nose plus four in packs on the side of the fuselage) in addition to the mid-upper, although some of the aircraft had only two pack guns and some had none at all. The nose could be retrofitted to earlier models, and I gather (but have seen no evidence to support) that some B-25Ds were so modified.
As well as the dirt problem with cannon, they were initially mounted on their sides. Oddly enough, this led to jams.... The eventual solution was to mount them the right way up and compromise the elegance of the Spit's wing by putting bulges on upper and lower wing surfaces.
As for mm vs inches, isn't a .30 caliber bullet the same width as the 7.62 mm? A 20mm shell must have been just over an inch in diameter? Unrelated, but one show on the Discovery Wings Channel features the Soviet "Frogfoot" SU-25, which flew in the 80's. A short video showed a small cannon (23mm?) firing straight into the metal below the cockpit canopy, with the pieces flying out like a dirt clod, but no apparent penetration through the metal.
Back to WW2-did the Spitfire, Hurricane etc .303 ever fire any incendiary rounds? Or did any normal bullets have magnesium tips, as with some US fighters such as the P-47, in order to better show where the impacts were?