Machine Guns versus Canons

[JohnT]

Can anyone answer a question that popped into my slow brain? I have read in several publications that RAF and to a lesser extent USAAF bombers were outgunned by Luftwaffe canon armed fighters who could sit outside the range of the defensive armament and use their canons with relative impunity to hit the bombers.

Thinking on this I follow the weight of fire and destructive effect of the heavier rounds will be obvious. What I can't get though is why the lighter machine gun round won't travel as far from bomber to fighter as the canon round going in the opposite direction. I guess the characteristics of individual weapons will be a factor but reading the books and magazines I got the impression all that was being said was that .303 rounds certainly didn't travel as far as canon rounds.

Anyone know why though or is it just wrong?

[davidelvy]

No doubt someone with greater technical knowledge will give a fuller answer, but cannon shells generally have a larger amount of propellant charge as well as a greater weight of projectile.

However, the Luftwaffe did not always have the advantage in terms of range of shot. Problems with getting an engine mounted cannon to work on early 109Es meant that many were only armed with machine guns. Later in the war the Germans started using 30mm cannon as a more effective weapon against bombers. However, the accurate range of these weapons was actually quite short.

[hacker]

it boiled down to this... For the RAF and the USAAF the main opposition were fighters so heavy cannons where not needed but for the Luftwaffe their main concern was the bombers. At first the Germans found big bombers difficult to knock down with just their machine guns. Even with the 20mm it was still difficult. The box formation was dangerous as once inside you had a lot of guns pointed at you. The 30 mm cannon was the answer. Though limited on range the idea was to get in quick and knock down a bomber with one pass. They even used small rockets just to get a good knock down hit in. The Me 262 had four 30 mm cannons and with its speed could get in quick and have a quick burst of cannon fire that usually knock out the bomber. But it was too little to late to make a difference.

Same in the pacific. The main opposition was fighters which were lightly armoured and no self sealing fuel tanks where as for the Japanese with was again the big bombers they had to deal with so they too opted for the cannon armed fighters

That is basically the reader digest version of the story

Edited May 28, 2015 by hacker

[Knight_Flyer]

I can recall reading somewhere a 303 caused less damage than a cannon round so even if it were able to travel the same distance, the RAF would still have to upgrade the guns on their fighter planes. Sorry this is also not answering your question

[Grayson]

The MK 108 30mm cannon had a relatively low muzzle velocity at about 550 (?) metres per second and had a defined and predictable arc through the air which good Luftwaffe pilots could use to their advantage in targeting a heavy bomber. The favoured munitions were called a mineshell and high explosive incendiary. The mineshell was made of drawn steel rather than forged which meant the shell/munition had a thinner construction and could pack more explosive giving more bang per hit.

It's estimated that between 20 to 25 rounds from a 20mm where needed to bring down a heavy bomber whereas only 3 to 5 30mm rounds would do the same job. Range of fire isn't as much an issue as a gunners ability to lead his fire onto a target, which is easier for a fast moving fighter to gauge against a slow moving bomber. Bomber crews suffered against faster moving fighters whipping through their fields of fire and overlapping fields of fire from multiple aircraft firing at a higher rate was considered the best way to offset this.

Remember this too, the Luftwaffe were firing into a target rich environment moving relatively slow by comparison.

Then the P 51's arrived.

[Troy Smith]

complex question, no simple answer, and with many variables.

So, that said, some factors

Note that main difference is cannon specifically fire an explosive shell, while a bullet relies on it's energy for damage.

the actual cannon also weigh more, have greater recoil, fire slower, and the ammo is heavier, so less can be carried, but they will do more damage if they hit, even if they lack velocity.

A battery of MG's will be more likely to score hits, and close up they worked very well.

IIRC in the BoB the Hurricane and Spitfre had 8 x 0.303 mg, with 14 secs ammunition, the bf109E-3 had 2 x 20mm, with 7 secs ammo, and 2x 7.9mm (= 0.303 approx), with 60 secs of ammo, though that's same fire power or a interwar biplane....

The cannon in Bf109 was lacked muzzle velocity, and tended to explode on contact, rather than penetrate.

As or bombers defensive armament, the US used 0.50 as standard, he British did start using 0.50 cal guns as well later, eg the Rose turret fitted to the Lancaster.

The 0.50 is not to be dismissed, it's a very powerful weapon, and in battery, can be devastating, note the P-47 with 8 x .50 is the only main fighter type that never had it's armament upgraded!

Later in the war the British switched to all cannon in fighters, eg Hurricane, Typhoon, Tempest, or as the main punch, Mosquito, Beaufighter, even the Spitfire was a slated for 4 x 20 mm cannon, which did become standard in the later Griffon versions.

The US stayed with 0.50, but they had a reliable weapon, and the infrastructure for it.

Post war most jets went over to cannon, though the US did continue with 0.50 into the 50's.

There are other members here who know a lot more about armament specifics, who hopefully will explain better.

In the specfic question about bombers, as the USAAF was basically day, the Luftwaffe did use some really big cannon in limited numbers to sit outside the range of the bombers, but mostly it was about speed.

the the cae of the RAF, the bombers defensive armament was not very effective unless close, and the gunners often acted more as lookouts, some gunner never fired their guns in anger.

Though the Luftwaffe wanted to get close to score lethal hits fast, the peak of this was when Schrage Musik

http://en.wikipedia.org/wiki/Schr%C3%A4ge_Musik

started to be widely deployed, the RAF didn't know about it, and had no under turret in most planes to look out even if they were aware of it!

It was almost always lethal, the technique was to fire into the wings to set the fuel tanks on fire, as hitting the bomb bay could be as dangerous to the attackers, as the attacker got close enough to be in the bombers under belly blindspot.

It's lethality was increased by it being issued to the better crews, one pilot on the Nuremberg raid shot down 4 bombers in quick succession, and used about 50 shells in total.

A much better description of the above can be found in Martin Middlebrook's 'The Nuremburg Raid'

http://www.amazon.co.uk/Nuremberg-Raid-30-31-March-1944/dp/1844158756

Along with one of the best guide for the layman on the entire RAF bomber offensive, and the German defences.

If you found that of interest, he did the same for the USAAF

http://www.amazon.co.uk/Schweinfurt-Regensburg-Mission-American-Raids-August/dp/0140066780

HTH

[davidelvy]

it boiled down to this... For the RAF and the USAAF the main opposition were fighters so heavy cannons where not needed but for the Luftwaffe their main concern was the bombers.

In the Battle of Britain it was the other way around. Although there were many encounters between fighters the crucial thing for the RAF was to stop German bombers attacking their airfields. Unless the Spitfires and Hurricanes got in very close it was difficult for them to inflict enough damage to bring down a bomber. Head on attacks were often used as it was easier to hit the soft parts (the crew). The need for heavier hitting weaponry was recognised before the war and cannon armed Spitfires did fly in the Battle, though at that stage their weapons were too unreliable to make an impact. It would also be wrong to think that cannon were not needed when engaging fighters as these were also protected by strategically placed armour plate and self-sealing tanks.

Another thing to bear in mind is that whilst .50 cal machine guns served the US forces well, they did try to develop a 20mm weapon. Like the British, this was based on the Hispano design. However, they did not fully adopt the British improvements and this, together with quality issues made the gun too unreliable. These problems were overcome, but had the weapon been effective at an earlier stage it would probably have been used.

Edited May 28, 2015 by davidelvy

[Giorgio N]

The range of a gun is a function of a few parameters, of which the main ones are:

- muzzle energy and velocity

- the capability of the bullet to retain energy, that mainly depends on its shape, weight and stability

Considering the above, it's not necessarily said that MGs had lower ranges as some guns scored poorly in nuzzle velocity.

Different story however if effective range is considered, as Troy already explained: A shell loaded with explosive can do great damage even hitting at low velocity, a bullet must have retained a certain amount of energy to cause damage. This energy will depend on the target, a soft wing skin will require less energy than a harder cockpit armor.

Useful range also depends a lot on the aiming devices.

If you want to know more, I can suggest searching for Anthony Williams website, he posted many articles on the subject and wrote a few books too.

[old thumper]

There were occasions where it was the RAF night bomber crew that spotted the night fighter and opened fire first, and other occasions where the night bomber crew spotted night fighters but withheld fire in order not to be spotted. If the German night fighter was able to spot the bomber first then it was possible to fire on RAF bombers while outside on their defensive armaments range but at night and with cloud really they needed to get closer to make things more certain

[JasonC]

If you want to know more, I can suggest searching for Anthony Williams website, he posted many articles on the subject and wrote a few books too.

That's the site I always recommend when this subject comes up. I've posted the link below to save people the search.

http://www.quarryhs.co.uk/miltech.htm

In particular, the following articles are directly relevant to the subject discussed here:

CANNON OR MACHINE GUN? : The Second World War Aircraft Gun Controversy

THE BATTLE OF BRITAIN: ARMAMENT OF THE COMPETING FIGHTERS

IDEAL WW2 FIGHTER ARMAMENT

WORLD WAR 2 FIGHTER ARMAMENT EFFECTIVENESS

regards,

Jason

EDIT: As an aside, I've often seen it written that the RAF evaluated both the 0.303" and the 0.5" machine guns early in (before?) the war, and found the latter no better in terms of penetration. I wonder whether the 0.5" in question was actually the Vickers 0.5", which had significantly less muzzle velocity and penetration than the Browning M2, which is the gun that most people think of when talking about a 0.5" HMG.

Edited May 28, 2015 by JasonC

[GMK]

As has been alluded to, hits on a target - any target - are meaningless unless sufficient energy is transferred into the target to do damage. In conventional bullets, energy is a function of velocity and mass. So, rifle bullets generally have a high muzzle velocity but (relatively) low mass. The terminal effect on a human target usually involves the projectile 'tumbling' upon impact, with associate tissue damage (Google temporary & permanent cavities). On a non-organic target, there's no soft tissue to magnify the effect of the energy transfer, just a small permanent bullet hole. Bringing the discussion back to aircraft targets, unless critical components are hit by high velocity/low mass projectiles, the target will continue to fly.

Heavy machine gun bullets, like those fired by the Browning 50 calibre, are almost four times heavier than rifle bullets (647 grains vs 174 grains): hence the increased damage inflicted by mass alone, not accounting for velocity.

Explosive shells, again, as mentioned above, don't have the same issues relating to velocity. So long as they fuse correctly, the cannon shell will inflict more damage.

Segue: Another consideration is the ability of aircraft to carry the weight of the cannon and its recoil mechanism. A good example of this is the aircraft-mounted 30mm M230 cannon (56kg cannon firing a 30 x 113mm round) vs the vehicle mounted Mk44 Bushmaster II (160kg cannon firing a 30 x 173mm round). As you can imagine, the range, velocity, projectile mass and explosive mass (hence destructive effect) of rounds fired by these two cannon are very different.

[Mitch K]

Tumbling or yawing of bullets was a factor even on aircraft. It was found that on impact with the outer skin (thin), bullets would tumble and then strike more vital components side-on, reducing the penetrating capability disproportionately. The writings of Tony Williams and Emmanuel Gustin, mentioned above, give enormous detail on things like actual penetration, the effect of explosive rounds exploding on impact versus post-penetration, the output to weight ratio of weapons and much, much more. An interesting discussion is the effect of a small number of very hard-hitting weapons versus a larger number of faster-firing, less damaging ones. The former is much more effective, provided the user can actually hit the target.

[GMK]

Mitch K, of course, a tumbling projectile has an effect on aircraft. I should've been clearer - soft tissue amplifies the effect of tumbling, creating more damage. Tumbling is different from yawing though: yaw is the difference between the trajectory of the projectile and the attitude of the projectile. Tumbling is when the trajectory of the projectile becomes eccentric by virtue of impact with the target or barriers between the muzzle and the target. Or, that's how I've always understood it.

[Giorgio N]

Tumbling does not necessarily occur and until the '60s it was considered negative as reduces penetration. It's only with the advent of small caliber high speed rifle bullets that ways were introduced to accentuate tumbling, be it through bullet design (5.45 Russian) or over-stabilization. Of course none of this applies to the MG vs. gun in ww2 debate, apologies for straying off topic a bit..

[Mitch K]

Mitch K, of course, a tumbling projectile has an effect on aircraft. I should've been clearer - soft tissue amplifies the effect of tumbling, creating more damage. Tumbling is different from yawing though: yaw is the difference between the trajectory of the projectile and the attitude of the projectile. Tumbling is when the trajectory of the projectile becomes eccentric by virtue of impact with the target or barriers between the muzzle and the target. Or, that's how I've always understood it.

GMK, me too.

AIUI, when striking a hard object, the bullet will do both: it can yaw AND tumble, depending on the material, its thickness, its density, the angle of impact and a number of other things. The take home is that at this point, when the round reaches any vital component, or armour plate, it doesn't strike point-first, but (to a greater or lesser extent) side-on, which greatly reduces penetration and may result in fuzes not functioning.

I read some very interesting data regarding the pilot armour on Blenheims. At normal incidence at the ranges described, armour-piercing rifle calibre rounds should have penetrated over 50% of the time. The effect of a layer of aircraft skinning was sufficient to reduce this to about 5% of the rounds actually penetrating. This was determined to be all to do with changes in the striking attitude of the bullets, and unconnected to the very slight loss of energy resulting from penetrating the aluminium alloy.

[Jon Kunac-Tabinor]

I recall reading somewhere that Russian P-39 pilots ( armed with the 37 mm cannon, and the two nose mounted .5 cal brownings - the Russians seems to be happy without wing guns of any kind it seems) had to be careful as the trajectories of the 37 mm gun and .5s were different - I assume the 37mm cannon was of lower velocity. So when firing they needed to remember which they were using - with the inference I suppose that they tended to use either the cannon or the MGs but not both at the same time?

What I find interesting is that by WW2s end most nations had gone over to multiple cannon in the 20mm to 30mm cal region, (or were at least planning to in the case of the USAAF & USN) - so presumably that was based on empirical evidence that a battery of such weapons gave the best destructive power in terms of fighter vs fighter, fighter vs bomber or fighter vs ground target engagements, or was the least worst compromise so to speak.

Jonners - enjoying reading this thread

[GMK]

Giorgio - thanks for that. Most of my education, training & experience is in modern small arms projectiles, armour and defeat mechanisms.

Mitch - really interesting regarding the Blenheim armour. Out of interest, was the V50 you mentioned for a 303 projectile or a 7.92mm one?

The stand-off between the aircraft skin & the armour plate thankfully means we avoid introducing discussions on wave-propagation through composite armour arrays! Yay.

[JasonC]

So when firing they needed to remember which they were using - with the inference I suppose that they tended to use either the cannon or the MGs but not both at the same time?

You'd still be able to set a convergence range at which the two trajectories intersected...

[Mitch K]

Giorgio - thanks for that. Most of my education, training & experience is in modern small arms projectiles, armour and defeat mechanisms.

Mitch - really interesting regarding the Blenheim armour. Out of interest, was the V50 you mentioned for a 303 projectile or a 7.92mm one?

The stand-off between the aircraft skin & the armour plate thankfully means we avoid introducing discussions on wave-propagation through composite armour arrays! Yay.

GMK, I *think* it was 0.303 armour piercing (as opposed to the API the RAF tended to use), which was considered to be (roughly) equivalent to the 7.92mm SMK - or at least near enough that the variation between the rounds used was of no greater impact than the other variabilities in the experiment!

[Mitch K]

You'd still be able to set a convergence range at which the two trajectories intersected...

This issue became that the "sweet spot" was small. It was OK if the pilot was a an excellent shot. If the pilot was a more average shot, the effectiveness was reduced. Also, "snap shots" are likely to be less effective.

[JasonC]

This issue became that the "sweet spot" was small. It was OK if the pilot was a an excellent shot. If the pilot was a more average shot, the effectiveness was reduced. Also, "snap shots" are likely to be less effective.

Doubtless true. Although given that the 37mm M4 fired at a mighty 150r/min, you'd have thought that hitting anything with a snap shot was largely a matter of luck anyway!

J.

Edited May 28, 2015 by JasonC

[gingerbob]

One factor that the RAF was very concerned about (at least from 1940 or a wee bit sooner) was armour- it is all well and good getting through the thin aluminium skin, but if it can't get through the armour, it is unlikely to hit the vulnerable things that the armour (presumably) is protecting. Thus the desire for what might be perceived as "larger than necessary" guns.

The actual question of range has not been addressed very well yet, nor am I qualified to answer it!

Very good observation from a couple of people that there's more to it than bore- 20mm cannon were not all created equal, and so on.

And as someone hinted at, if the pilot (or gunner) can't hit the target, it doesn't really matter what armament you're firing! Or, put another way, the probability of making contact is a consideration in the overall equation.

bob

(Note: a number of posts came in while I was writing this...)

Edited May 28, 2015 by gingerbob

[Jon Kunac-Tabinor]

Bob of the Ginger raises a good point: - if you can't get your guns on target it's of little matter .

It would be interesting to see what percentage of air to air kills in WW2 were of the classic hit and run "bounce" variety ( as opposed to twisty dogfight types) where the victim isn't really aware of whats happening until its too late.

I'm guessing when you have time to set up an attack like that - your chances of scoring hits are far better, although the introduction of the gyro sight into the RAF was also meant to have improved deflection shooting for average pilots too.

Jonners

[Mitch K]

Bob of the Ginger raises a good point: - if you can't get your guns on target it's of little matter .

It would be interesting to see what percentage of air to air kills in WW2 were of the classic hit and run "bounce" variety ( as opposed to twisty dogfight types) where the victim isn't really aware of whats happening until its too late.

I'm guessing when you have time to set up an attack like that - your chances of scoring hits are far better, although the introduction of the gyro sight into the RAF was also meant to have improved deflection shooting for average pilots too.

Jonners

The other, important case is the deliberate attack, for example on formations of bombers, which are neither a bounce nor a dogfight. This was the particular scenario that drove the Luftwaffe toward heavier weapons. Some authors have suggested the rather lukewarm position that the US took toward aircraft cannon in WW2 was driven in large part because they were dealing with fast-moving targets that were not heavily protected and or well-endowed with defensive weapons (like A6M's and Bf-109's rather than B-17's).

The search for a "one size fits all" gun armament, suitable for dealing with fast, hard-manouvering fighters, tough, well-protected bombers and strafing ground targets whilst not over-burdening the carrier aircraft and the logisitic system didn't get solved during WW2, continued through the Cold War and, to my mind at least, is still going on today.

[gingerbob]

Getting back to the range question again, while in theory it would work to stand out of range and lob fire at the enemy, in practice it didn't generally work that well- accuracy suffered dramatically, as well as the 'energy' of the hits, as discussed. And once there were escort fighters about then there was no "out of range"!

bob