20/20 Hindsight - different armament?

[Jank]

"Perhaps we should be wondering if the RAF got it right with opting for eight 0.303"

That was funny.

[Tony Williams]

Perhaps we should be wondering if the RAF got it right with opting for eight 0.303"? Wouldn't four or six 0.5" have been better? Come the Battle of Britain, such puny rifle calibre guns were only saved by the Dixon (usually mistakenly referred to as De Wilde) ammunition.

Aircraft went through a process of up-armouring as a result of battle experience during 1940. At the start of the fighting, eight .303s were probably the best armament of any fighter in service. As aircraft toughened up, so .303s became less effective. By the end of the BoB, a quartet of .50s would probably have been better (although heavier). Even so, the RAF continued fitting .303s to fighters for several years, so they can't have regarded them as useless.

The B Mk VI ("De Wilde") incendiaries were a definite improvement on any other type at the time, but they weren't that common initially. See my analysis of BoB armament HERE

The RAF had realised that the .303 would no longer be adequate as soon as planes started to adopt armour plate, and were planning as early as 1935 for fighters armed with 20mm cannon - but the Hispano took longer than expected to de-bug, so it just missed contributing to the BoB.

Tony Williams: Military gun and ammunition website and discussion forum

[Jank]

It wasn't just the advent of armor plate that rendered the .303 less than adequate but the structural and other "hard" components of the aircraft itself.

A .303 with Mk. I AP would penetrate just 5mm of armor plate at 200 yards at 20 degree deflection. A .50 AP round under the same circumstances would penetrate 14mm. Even at 600 yards, the .50 under the same circumstances could still penetrate 9mm of armor plate. Obviously, it was far easier to critically damage your opponents engine with a few .50's than a dozen or more .303's.

Yes, obviously the Brits didn't regard it as useless but their ongoing use of it does not mean it was effective relative to other available armaments like the .50 either. Case in point. The USAAF persisted in using the .50 on its F-86 when it would have been far more effective with even three 20mm's. Many, many Migs made it back to base peppered with .50 rounds.

[Tony Williams]

It wasn't just the advent of armor plate that rendered the .303 less than adequate but the structural and other "hard" components of the aircraft itself.

I agree. The RAF were also aware of this, which is why they decided in the mid-1930s that they needed to fit their fighters with eight of the guns, at a time when most fighters in service only had two. They were working on the calculation that a high volume of hits would compensate for the low effectiveness of each one, but this was not entirely successful.

The Luftwaffe also perservered with rifle-calibre guns, of course, with the 109 and 190 carrying 7.9mm cowling guns until about 1943 IIRC.

Tony Williams: Military gun and ammunition website and discussion forum

[Soren]

Interesting discussion guys.

As to armor penetration and the effect the size of the incoming projectile has is here explained by Robert D. Livingstone, Co. author of "World War II Ballistics: Armor and Gunnery".

"Armor obliquity effects decrease as the shot diameter overmatches plate thickness in part because there is a smaller cylindrical surface area of the displaced slug of armor which can cling to the surrounding plate. If the volume which the shot displaces has lots of area to cling to the parent plate, it resists penetration better than if that same volume is spread out into a disc with relatively small area where it joins the undisturbed armor. Plate greatly overmatching shot involves the projectile digging its own tunnel, as it were, through the thick interior of the plate. It was found experimentally that the regions in the center of the plate produced the bulk of the resistance to penetration, while the outer regions, near front and rear surfaces, presented minimal resistance because they are unsupported. Thus, an overmatched plate will be forced to rely on tensile stresses within the displaced disc, and will tend to break out in front of the attacking projectile, regardless of whether the edges cling to the parent material or not. Plate obliquity works in defeating projectiles partly because it turns and deflects the projectile before it begins digging in. If there is insufficient material where the side of the nose contacts the plate, stresses will travel all the way through the plate and break out the unsupported back surface. The plate will fail instantaneously rather than gradually".

"You can angle the armor any way you want, and beyond a certain point of shot overmatching plate, the obliquity will cease to be relevant. In fact, at certain conditions of shot overmatching plate, the cosine rule is broken and the plate resists less well than the simple cosine relationship would predict (LOS thickness is greater than effective thickness). The above only applies to WWII era AP and APC/APCBC, and WWII sub caliber ammunition. The long rod penetrators of today are greatly overmatched but they bring so much energy to the plate that they penetrate by "ablation" in which both projectile and armor behave like fluids. Hollow charge also enters the field of fluid dynamics, with a very thin jet penetrating overmatching armor with ease, regardless of obliquity"

Was he's talking about here is the effect of the T/D coefficient between the incoming projectile and the armour it opposes.

[merlin]

I note in an earlier reply Tony referred to the "De Wilde" incendary shells for the 0.303" machine guns. Isn't it about time the De Wilde reference was dropped - it was only retained to fool the Germans! The real hero was Captain Dixon, who realised that the De Wilde shell being hand made without any 'measured' amount ingredients, couldn't be mass-produced. It was fortunate that he unofficially conducted tests until he came up with the solution - which was passed on the the Americans!
Hence he deserves the credit for his achievement.

Sorry for being slightly off-topic!!

[Tony Williams]

That is quite true, but they are still popularly known as "De Wilde" bullets. if I want to be technically precise, I refer to them as the B Mk VI (superseded by the B Mk VII), which is their official designation.

[renrich]

Earlier in this thread someone mentioned an English ace who always checked to see if he was in a turn before firing his guns. I believe that was Stanford Tuck and he was not checking whether in a turn but checking whether he was in a skid or uncoordinated flight. I also believe that the eight gun armament of the British fighters was partly because of the Tactics they were using and because of the poor marksmanship of the pilots. They theorised that they would open fire at long ranges with a lot of guns and get hits because of the many bullets in the air. Sort of a shotgun approach. Also I don't know if this has been mentioned but a significant number of Corsairs were armed with 4- 20mm cannon in WW2 and some night fighter versions of the Hellcat had 2-20mm cannon plus 4-.50 MGs.

[Tony Williams]

I also believe that the eight gun armament of the British fighters was partly because of the Tactics they were using and because of the poor marksmanship of the pilots. They theorised that they would open fire at long ranges with a lot of guns and get hits because of the many bullets in the air. Sort of a shotgun approach.

No - the decision to go to eight guns was taken in around 1934/5, as a result of theoretical studies which showed that the increasing speed of aeroplanes meant that a pilot may only be able to fire at a target for about two seconds (IIRC). So they did some sums to work out how much damage one machine gun could do to an aircraft in two seconds, and reckoned that they would need eight of them to do the job.

They started out with the guns harmonised for 400 yards, on the assumption that a typical attack run would start at that distance and finish off at 200 yards. They estimated that the spread of fire at short range would cover the fuselage and engines of a twin-eingined plane, so all the bullets should still be hitting. Early WW2 experience showed these figures were too optimistic, so they dropped the harmonisation range to 250 yards.

The RAF became concerned at standards of pilot accuracy in deflection shooting in the late 1930s, so started working on the gyro gunsight. That had no effect on the choice of armament though.

[renrich]

Thanks Tony for your explanation. I had read somewhere about the theory you discussed but was quoting from memory which was quite hazy. According to John Lundstrom in "The First Team" the European air forces did not place much reliance on deflection shooting in contrast to the US Navy perhaps partly because of visibility problems in inline engined a/c. An aside, I saw gun camera film of a German fighter firing at a P38 from the 6 o clock position about 30 degrees high. What a target with a lot of vital parts.

[renrich]

PS, good work of fiction, "Piece of Cake" can't remember author goes into British fighter tactics and gunnery it seems with some accuracy. Good book!