Why did the RAF persist with the .303 throughout the war?

[swampyankee]

I never understood the British idea of pointing all of your guns in different directions. They were already using a popgun anyway, the only real way to make a 30 caliber weapon effective against airplanes is to point them all at the same place and get a good dense pattern on your target. Trying to shoot down an HE111 with one 303 while the other 7 shoot off into space had to be any excercise in futility and extremely frustrating for the British pilot. It would be like hunting geese with an open choked shotgun and #9 birdshot. Even if you hit him with a few pellets, the pattern isnt dense enought to cause enough damage to bring him down.

On the other hand, if you have all 8 of them shooting into a 3 foot by 3 foot square at 100 yards, it would act like a buzzsaw. Each round itself is still underpowered, but in concentrated form it would still be MUCH more effective than only one gun being on target while the other 7 waste ammo shooting off into space.

According to information on Tony William's site, the RAF originally set the guns to converge at one point; after war experience they stopped doing so. Possibly, this was because aircraft were not point targets, and the bullets that missed the point of aim still hit other parts of the airplane.

 

[Ivan1GFP]

Keep in mind the time period in which these fighters and their armament were chosen:

In the mid 1930s, the typical fighter armament was still only two or perhaps, if you were forward thinking, four rifle caliber machine guns.
The Japanese kept this with their Ki-27 and even Ki-43-I fighters.
The Germans only had 4 x 7.92 mm MG with the Me-109.

This wasn't quite as ineffective as a typical infantry rifle though. Most nations used different ammunition in their machine guns and especially aircraft machine guns. The ammunition was loaded a bit hotter and may have been armour piercing or incendiary / tracer as well. Funny thing was that although .303 Rifle ammunition still had Cordite as a propellant, the machine gun ammunition used a much less erosive propellant.

Also, except for MG ammunition intended for overhead fire for training, typical MG ammunition isn't all that accurate. So.... The idea of common ammunition between aircraft and infantry is not correct. Ammunition tends to be packaged for an intended weapon and used as packaged.
Folks don't break down 5 round stripper clips to load a MG belt or de-link a MG belt for infantry use.

Some folks, and I believe the British did this as well, harmonised guns in pairs so that the outboard guns converged a bit further out. The theory at the time expected fighter armament to be much longer ranging than 300 yards or less as it turned out in action.

The early 20 mm installations were VERY unreliable. Just about any G load from maneuvering while firing and the gun stops working. Also, the drums typically only carried 60 rounds or so. So, assuming everything worked, you only got about three good squirts from the cannon before they became dead weight. Later installations carried more ammunition, but that is what they started with in the first installations.

The German and Japanese cannon at the time were no better and even had worse ballistics.

Also consider that armour was not installed in most fighters of the time.
Seems to me the .303 Browning MG was a pretty reasonable selection for the time.

- Ivan.

 

[davebender]

Two centerline mounted machineguns (preferably .50cal / 13mm) is viable for shooting down fighter aircraft. I think that's why late war Me-109 kept the cowl guns even though they had cannon.

 

[Greyman]

I can see how the .303 would have been the best choice at the time of the BoB

It wasn't, and the first ones to tell you that would be the British Air Ministry. They chose the .303 Browning to replace the Vickers Mk.V in 1934. By 1937 they had already decided that the 20mm Hispano should replace it. But, you can't just snap your fingers and change something like that. Reality got in the way - right up until 1945.

I'm surprised that after the US entry into the war there was (possibly) not the option of procuring guns from there.

It was possible, but the British didn't want it, for reasons already mentioned. They were clamouring for more Hispano guns, which the US was trying to produce, but when the requirement for Spitfire guns was halved (the decision being made to only equip them with two cannon) the British could rely on their own production.

I never understood the British idea of pointing all of your guns in different directions.

The idea was 'is it wise to put all the eggs in one basket?' If you miss (which most pilots did) you miss with all. It wasn't necessarily 'the British idea' either. Most Air Forces spread their guns somewhat.

 

[Jabberwocky]

Economics was the prime driver, but institutional inertia, the early reliability of the Hispano and previous assesments of the .50 all helped the RAF to retain the .303, even when they knew it was comparatively ineffective.

The UK had the .303 Browning gun and .303 ammunition in production and had significant stockpiles of ammunition. The gun was cheap, reliable and until the introduction of increasing amounts of armour plate on German bombers, quite effective.

The RAF didn't think they neded a .50 cal class weapon. Their assesment of the .50 Vickers and (early) M2 Browning conducted in the 1930s found that the heavy machine gun was neither fish nor fowl: it didn't have the rate of fire or pattern density of the .303 nor did it have the hitting and explosive power of the larger cannon.

In later trials against protected fuel tanks, the .50 cal rounds tested were more likely to penetrate and cause large holes, but were not that much more likely to start fires than the .303 (mostly due to the inadequate design of the early incendiary rounds). So putting many .303 rounds onto a target rather than fewer .50 cal rounds made sense, at least from the results of the trials.

The early Hispano had some reliability issues. These related to the all sorts of things, including lightly struck ammunition, the feed mechanism/magazines (about half of all stoppages were feed related), the gun mounting, the recoil springs, gun heating, ejection ports and fouling of the gun mechanism from grit/contamination. These were solved progressively through the war, but the RAF retained the .303s as a back up in case the 20 mm malfunctioned.

Self-sealing fuel tanks and armour plate really only began to appear on German bombers from mid-1940 onwards. For the RAF to recognise the .303 is less than wholly effective takes time. Then they have to decide to do something about it, actually do it and then distribute the solution. All that takes a while. Some pilots still favoured the .303 over the cannon well into 1941.

 

[pinsog]

The idea was 'is it wise to put all the eggs in one basket?' If you miss (which most pilots did) you miss with all. It wasn't necessarily 'the British idea' either. Most Air Forces spread their guns somewhat.[/QUOTE]

But that doesn't make sense. A few random bullets from one rifle caliber machine gun is unlikely to bring down an HE111, DO17 or JU88. I understand that many British pilots during the BoB were not well trained, especially in gunnery and that they had to get REALLY close to hit anything. But again, pointing all of your guns in different directions will not give you enough damage for a kill. What is the point of aiming each gun in a different direction just to be able to claim you hit an aircraft? "Hey guys, I put 20 bullets into a German bomber today. It will take them at least 10 minutes to patch that up when they get back" If you are going to shoot at enemy bombers, your goal should be to destroy them, not hit them randomly with a dozen or so bullets while your other guns are blazing away off in a different direction. Also, if you are going to close to less than 50 yards on an enemy bomber, which untrained British pilots often did, you should be able to hit it with your guns concentrated in a small target area.

 

[Shortround6]

It wasn't, and the first ones to tell you that would be the British Air Ministry. They chose the .303 Browning to replace the Vickers Mk.V in 1934. By 1937 they had already decided that the 20mm Hispano should replace it. But, you can't just snap your fingers and change something like that. Reality got in the way - right up until 1945.

Quite right, and the reason they went with the Browning instead of keeping the Vickers was the the Vickers had a rather alarming tendency to jam. The Jams could often be cleared fairly easily but required some sort of access to the gun. in WW I and shortly thereafter the RAF had used Lewis guns in wing (or underwing) mounts because of the reliability issue. This rather rules out adopting the .5 Vickers gun as is at it would have the same jamming problem.

It was possible, but the British didn't want it, for reasons already mentioned. They were clamouring for more Hispano guns, which the US was trying to produce, but when the requirement for Spitfire guns was halved (the decision being made to only equip them with two cannon) the British could rely on their own production.

to add to that, the British had tested the .50 cal Browning back in the trials that lead to the adoption of the small Browning. But the .50 cal Browning of the late 20s and early 30s was NOT the .50 cal Browning of 1942/43. It used ammo that was several hundred fps lower in velocity and had a max cycle rate of under 600rpm. This is for a gun in a test stand with a "short" belt of ammo. Trying to pull a long belt slowed the gun down. When synchronized to fire through the propeller the cycle rate fell to under 500rpm and in some cases was closer to 400 rpm on some of the P-40s the British first got. The M2 Ball ammo ( and other loads/types to correspond) don't show up until the mid/late 30s. The US does not improve the rate of fire until some point in 1940. Before or after the BoB I don't know.
I don't have the production figures at hand and so may be wrong but if .50 cal production followed most of the rest of US production you had a trickle in 1940/41, a fair number in 1942, a river in 1943 and an avalanche in 1944 and were trying to figure out how to stop it in 1945.
Just found some figures, Production of ALL types of .50 cal machine guns from July 1 1940 on. 1940-5155 guns, 1941-49,479 guns, 1942- 347,492 guns, 1943-641,638 guns, 1944-677,011 guns, 1945-239,821 guns.
It would not be until some point in 1943 that the US would be in a position to supply any real quantity of guns on a steady basis even with very careful accounting and not stockpiling guns for future needs. ( how many air frame programs were running behind schedule or other needs that fluctuate).

The idea was 'is it wise to put all the eggs in one basket?' If you miss (which most pilots did) you miss with all. It wasn't necessarily 'the British idea' either. Most Air Forces spread their guns somewhat.

Against a small fighter fuselage a lot of these patterns might leave something to be desired. Against something like a He 111 as long as the pilot did his job ( the biggest IF in the question) some of the patterns offered a 50-75% hit rate out to 400 yds from a 6 oclock ( 0 deflection) aiming point. Spitfire patterns changed a number of times during the war and went from ( apparently) all guns in line converging at different distances, starting at 350 yds or more and changing to 250 yds (or less?) with the eight machine guns to some rather complicated patterns with the 20mm guns forming a figure 8 at the cross over distance and the 4 MGs aligned (or mis aligned ) to hit at different heights and horizontal distances at ALL ranges.

In favor of the wide spread for bomber interception was the fact that actual kills were NOT the objective. Stopping the bomber before it reached it target was. If you can damage the bomber and force it to turn back/jettison it's load you have succeeded in defending the target. Granted a damaged bomber bomber can be repaired and fly other missions but on any given day/night the more bombers the fighters can put bullets into the greater number they may stop even if the total kills for that day are bit lower than more concentrated fire.

Some "spreads" are pretty nominal.

Convergence diagram for a P-47;

Notice that even if the inner guns were set for 250 yds and the outer ones for 350 yds it is possible to have ALL guns hitting in a area about 12 feet wide from 100 yds to 400 yds range. With guns starting at around 18-20 ft apart that doesn't seem too bad.

 

[Shortround6]

The idea was 'is it wise to put all the eggs in one basket?' If you miss (which most pilots did) you miss with all. It wasn't necessarily 'the British idea' either. Most Air Forces spread their guns somewhat.

But that doesn't make sense. A few random bullets from one rifle caliber machine gun is unlikely to bring down an HE111, DO17 or JU88. I understand that many British pilots during the BoB were not well trained, especially in gunnery and that they had to get REALLY close to hit anything. But again, pointing all of your guns in different directions will not give you enough damage for a kill. What is the point of aiming each gun in a different direction just to be able to claim you hit an aircraft? "Hey guys, I put 20 bullets into a German bomber today. It will take them at least 10 minutes to patch that up when they get back" If you are going to shoot at enemy bombers, your goal should be to destroy them, not hit them randomly with a dozen or so bullets while your other guns are blazing away off in a different direction. Also, if you are going to close to less than 50 yards on an enemy bomber, which untrained British pilots often did, you should be able to hit it with your guns concentrated in a small target area.[/QUOTE]

If they got within 50yd the guns would mostly all hit, the guns were NOT pointed THAT badly.

According to the diagram for Spitfire Bullet pattern 1, from the 6 O'clock postition, the out board guns would hit a He 111 just out board of the engine nacelles, the middle pair would hit just inboard of the engine nacelles with an over lapping pattern and the inner guns hitting just outboard of the wing root fairing. the 75% zone for each gun was about the thickness of the He 111s wing in diameter. as the range gets longer the 75% zones get bigger but they move in closer to the fuselage and blend together more until at 300 yds ( with a 350 yd convergence) they look like a side ways figure 8 that has been traced over several times and overlaps a bit. The 75% zone from each and every gun looks to be about 80-90% on the He 111 fuselage, at 400 yds the guns have crossed over and the 75% zone has grown greater than the diameter of the He 111 fuselage.

The Diagram can be found on page 93 of Tony Williams and Emmanual Gustin's book "flying Guns World War II.

Some British pilots, even with some training were opening fire on target sleeves at up to 1000 yds even when instructed to open fire at 300 yds.

 

[Greyman]

But that doesn't make sense. A few random bullets from one rifle caliber machine gun is unlikely to bring down an HE111, DO17 or JU88. I understand that many British pilots during the BoB were not well trained, especially in gunnery and that they had to get REALLY close to hit anything. But again, pointing all of your guns in different directions will not give you enough damage for a kill. What is the point of aiming each gun in a different direction just to be able to claim you hit an aircraft? "Hey guys, I put 20 bullets into a German bomber today. It will take them at least 10 minutes to patch that up when they get back" If you are going to shoot at enemy bombers, your goal should be to destroy them, not hit them randomly with a dozen or so bullets while your other guns are blazing away off in a different direction. Also, if you are going to close to less than 50 yards on an enemy bomber, which untrained British pilots often did, you should be able to hit it with your guns concentrated in a small target area.

To illustrate the point, I'll take things to a ridiculous extreme ...

Imagine if the Spitfire I was armed with eight 30mm ADEN guns. Would you not agree that harmonising them to a single point would be a waste? Would it not be better to create a pattern that conforms to the shape on an enemy aircraft from 200 yards to 400 yards? Instead of just a single point at 250 yards.

The disconnect here is what constitutes 'lethal density'. The British (AFDE specifically) had their data from before the war, and that's what they went on.

How armoured were German pilots, coolant and oil systems in 1939?
What was the average aiming error of British pilots from gun camera exercises?
How effective is massed fire from German bomber formations? Is closing to 50 yards before firing a good thing to do?

 

[Greyman]

Spitfire patterns changed a number of times during the war and went from ( apparently) all guns in line converging at different distances, starting at 350 yds or more and changing to 250 yds (or less?) with the eight machine guns to some rather complicated patterns with the 20mm guns forming a figure 8 at the cross over distance and the 4 MGs aligned (or mis aligned ) to hit at different heights and horizontal distances at ALL ranges.

Basically it went like this:

Sep 1938 - harmonised to a point 350 yards ahead --- 'concentrated pattern'
c.Sep 1939 - harmonised to a large box pattern 400 yards ahead --- 'horizontal harmonization' (British Forces in France continued to harmonise to a point 350 to 150 yards ahead, depending on Squadron)
c.Dec 1939 - two squadrons switch to a large circular pattern 200 and 400 yards ahead --- 'circular harmonization'
Jan 1940 - ten squadrons switch to concentrated pattern
Feb 1940 - full RAF switch to concentrated pattern
c.mid 1942 - 'spread pattern' (which you somewhat described)

 

[Shortround6]

Thank you, the "Spread pattern" is shown somewhere in the book I mentioned earlier but it it is a real pain to describe in text.

I too will carry something to a ridiculous extreme to agree with you.

Barrage balloons and smoke generators brought down very few bombers but were an important part of air defense because they lowered the effectiveness of the enemy bombers. They forced them to fly higher or helped hide the targets from the bomb aimers.
Likewise early AA guns scored few kills but often made bomber crews drop early/late/wide or pick another target.

Many times a weapon's/tactic's effectiveness cannot be measured by simple kill/loss ratios.

 

[Greyman]

One of the very reasons to continue to carry .303-inch guns: it forces your enemy to armour against .303-inch guns. It's pointless to try and armour against Hispano 20-mm rounds, but if you're carrying .303 Brownings - now your enemy has to carry hundreds of extra pounds in armour.

 

[pinsog]

.

 

[pinsog]

To illustrate the point, I'll take things to a ridiculous extreme ...

Imagine if the Spitfire I was armed with eight 30mm ADEN guns. Would you not agree that harmonising them to a single point would be a waste? Would it not be better to create a pattern that conforms to the shape on an enemy aircraft from 200 yards to 400 yards? Instead of just a single point at 250 yards.

The disconnect here is what constitutes 'lethal density'. The British (AFDE specifically) had their data from before the war, and that's what they went on.

How armoured were German pilots, coolant and oil systems in 1939?
What was the average aiming error of British pilots from gun camera exercises?
How effective is massed fire from German bomber formations? Is closing to 50 yards before firing a good thing to do?

Your extreme example doesn't make sense. A single 30mm ADEN cannon could easily bring down any aircraft in WW2, perhaps finding the B29 a bit more difficult. The 303 (or any 30 caliber or 8mm rifle cartridge) is terribly underpowered for shooting down aircraft in WW2 (possibly excepting the early war biplanes and other obsolete aircraft). Rifle caliber machine guns must be concentrated to be effective on the aircraft the Germans were using because the individual cartridge was weak. Just like ants, an individual ant attacking a scorpion or large spider is not going to fair well, a swarm of them can kill about anything. If you are forced to hunt crows or ducks with #9 birdshot, you better use a full choke so you hit your target with a good chunk of the pattern. If you use #9 birdshot with a cylinder bore on a crow, about all you are going to do is make noise, you probably wont even knock any feathers off, much less bring down the target.

If they stuck me in a Spit or Hurricane during the BoB, I would tell them to put all 8 guns in as small a box as possible at 100 yards.

 

[CobberKane]

One of the very reasons to continue to carry .303-inch guns: it forces your enemy to armour against .303-inch guns. It's pointless to try and armour against Hispano 20-mm rounds, but if you're carrying .303 Brownings - now your enemy has to carry hundreds of extra pounds in armour.

That's one of the more interesting pieces of logic I've heard in a while. For starters armour could and did frequently stop 20mm rounds during WWII. Enemy fire was as likely as not to strike at an angle, where all or much of the energy could be negated by armour plate. Also, armour wasn't just installed to counter airborne LMGs; it was also there to provide protection from shrapnel and bullets from all calibres of ground fire.
By your reasoning, had allied aircraft been armed exclusively with cannon by 1944, the Germans would have responded by stripping all the armour from their fighters. A little counter-intuitive, to put it mildly

 

[Shortround6]

If they stuck me in a Spit or Hurricane during the BoB, I would tell them to put all 8 guns in as small a box as possible at 100 yards.

That rather limits your options as at 200yds the guns would as spread out as they are in the plane. Roughly for a Spitfire about 7 ft from the center line, then just under 9ft , just over 9 ft and about 12 ft. With a 200yd cross at 100 yds the guns are hitting at half their actual installed distances. Please note that on a P-47 the closest guns are about 9 ft from the center line.

With a 200 yd cross ALL guns would be hitting in an area about 6 feet wide anywhere from 150-250 yds range. with a 250 yd cross the sweet spot is a little further away but is also a bit longer.

Your 100 yd cross means your outer guns are 24ft apart at 200 yds and your 4 "middle" guns are about 18ft apart at 200yds. At 300yds you have bullets all over the sky, your outer guns are now hitting 48 ft apart and the "middle guns" are 36ft apart, even the inner guns are about 28 ft apart.

You HAVE to get close to 100yds to have an effective pattern. Forcing ALL your pilots to close to 150 yds and under is going to increase losses from collisions and hitting debris.

 

[pinsog]

That rather limits your options as at 200yds the guns would as spread out as they are in the plane. Roughly for a Spitfire about 7 ft from the center line, then just under 9ft , just over 9 ft and about 12 ft. With a 200yd cross at 100 yds the guns are hitting at half their actual installed distances. Please note that on a P-47 the closest guns are about 9 ft from the center line.

With a 200 yd cross ALL guns would be hitting in an area about 6 feet wide anywhere from 150-250 yds range. with a 250 yd cross the sweet spot is a little further away but is also a bit longer.

Your 100 yd cross means your outer guns are 24ft apart at 200 yds and your 4 "middle" guns are about 18ft apart at 200yds. At 300yds you have bullets all over the sky, your outer guns are now hitting 48 ft apart and the "middle guns" are 36ft apart, even the inner guns are about 28 ft apart.

You HAVE to get close to 100yds to have an effective pattern. Forcing ALL your pilots to close to 150 yds and under is going to increase losses from collisions and hitting debris.

You might bump it out to 150 yards, but I wouldn't want it to be any further than that due to the poor hitting power of the 303. One of the reasons given for using the high rate of fire 303's in place of the Browning 50 during the BoB, is that the relatively untrained British pilots could shoot worth a crap so they would just spray random fire at German bombers hoping to hit them. If that was indeed the case, then 100 to 150 yards is probably farther than they could hit anything anyway. Now a P47 would be a different deal. The 50's could be set much farther out since they have so much more power.

 

[Shortround6]

I think you have a rather poor opinion of of the .303 ammo, which seemed to work just fine for the Japanese in a number of their aircraft guns in Dec 1941 and a good part of 1942.

.303 ammo doesn't turn into spitballs at 200yds. It may have been far from ideal but it did manage to shoot down several thousand Axis aircraft.

And effective range would vary with altitude.

A major problem is range estimation and leading (deflection shooting). Time of flight becomes rather important.

The 250 yard cross is going to give around 110-120 bullets into about a 6ft wide by 2 ft high area in one second for a bit if a distance on either side of the actual cross point. If this isn't concentrated enough what is? (and that is allowing for a 75% hit zone, a 1005 hit zone might be 8-9 feet wide and 3-4 feet high and up the hits to 150-160 in one second). Shortening the effective range of the fighter to 150 yds or less is not the answer. It will be much harder to get into effective firing positions. it make s range estimation much more critical ( if a pilot you thought he was a 300 yds was actually at 800-1200yds what happens to your 100 yd convergence if if he thinks he is at 100 but is actually at 300yds? see above spreads in previous post.

The high rate of fire .303 in the BoB was really high because the .50 cal Browning was lucky it could reach 600rpm synchronized at the time. Throw that in with the weight of .50 cal guns and ammo and it was no contest. for the weight of eight .303 Brownings and 350 rounds per gun you could get four .50 cal guns and 75-80 rounds per gun. 8 seconds of firing time at 40 rounds per second vs 17 seconds firing time at 150-160 rounds per second. Merlin III was good for 880 hp for take-off unless you used emergency boost.

 

[Greyman]

Your extreme example doesn't make sense. A single 30mm ADEN cannon could easily bring down any aircraft in WW2 ... The 303 (or any 30 caliber or 8mm rifle cartridge) is terribly underpowered for shooting down aircraft in WW2 (possibly excepting the early war biplanes and other obsolete aircraft).

I'm not sure how else to get my point across, sorry. All I can say is that the British believed the .303 Browning to be more effective than you do.

That's one of the more interesting pieces of logic I've heard in a while. For starters armour could and did frequently stop 20mm rounds during WWII. Enemy fire was as likely as not to strike at an angle, where all or much of the energy could be negated by armour plate. Also, armour wasn't just installed to counter airborne LMGs; it was also there to provide protection from shrapnel and bullets from all calibres of ground fire.
By your reasoning, had allied aircraft been armed exclusively with cannon by 1944, the Germans would have responded by stripping all the armour from their fighters. A little counter-intuitive, to put it mildly

I understand what you're saying, and it is more complicated than that, and isn't my reasoning, but - I can't find the document where this thought is mused (among a mass of RAF/Air Ministry/etc. correspondence of how to deal with this new Fw 190).

I meant it more as a small quip to toss onto Shortround's pile and not an Official Ministry of the Air Reason 4.a) on why .303-inch calibre was used.

You might bump it out to 150 yards, but I wouldn't want it to be any further than that due to the poor hitting power of the 303. One of the reasons given for using the high rate of fire 303's in place of the Browning 50 during the BoB, is that the relatively untrained British pilots could shoot worth a crap so they would just spray random fire at German bombers hoping to hit them. If that was indeed the case, then 100 to 150 yards is probably farther than they could hit anything anyway. Now a P47 would be a different deal. The 50's could be set much farther out since they have so much more power.

Hitting power of .303 rounds wont be much effected by an extra hundred or so yards. Accuracy will, hence the spread patterns.

 

[CobberKane]

I'm not sure how else to get my point across, sorry. All I can say is that the British believed the .303 Browning to be more effective than you do.



It would seem so, wouldn't it? At least when combined with cannon. It was mentioned earlier that the .303s would give the Spit, Mossie etc at least some capability after the Cannons ran out of ammo. I can see that being true with regards to the Spit V with its drum fed Hispanos, but later Spits had belt fed cannon and twice the ammo load - and they could have carried more again if the Brits had considered it worthwhile making room by ditching the LMGs. Standardisation of calibre with small arms also seems logical, but the Aussies used Lee-Enfields and Brens too, yet they still chose to put HMGs on their Beaufighters. Maybe it was a case of, if it ain't broke don't fix it, like the USAAF sticking with the .50 because going with cannon would have been a major hassle for extra firepower that wasn't really needed anyway.