Machine Guns versus Canons

[Jon Kunac-Tabinor]

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.

True - I sought of meant that to be included in my "planned" attacks statement - but the point is well made

It's interesting that both the LW and Japanese went for successively larger calibre weapons in this role - up to 50 mm to even 75 mm, plus unguided rockets ( which I'd always though were more formation breaker-uppers).

I suppose the battery of 4 x 30 mm Adens the Hunter carried was again for its intended role as Soviet Bomber interceptor. Mind you and going off subject a tad - lobbing a nuclear tipped Genie into a cloud of Soviet bombers would have ruined everyones day!

Back to the VVS P-39s again - the inference of the article was that pilots preferred head on attacks against 190s & 109s using just the 37 mm cannon, so had to adjust their aiming for the trajectory of this weapon. Apparently it was rather off putting having someone shoot heavy calibre shells directly at you - and 1 hit was enough to splash a 109 or 190.

The same article also had a statement which I've always rather liked, and says to me something about the fighter pilots aggressive spirit, to whit ( and I paraphrase) "You can fly a P-39 in such a way as to maintain its engine life, or in such a way as to shoot down Germans, but not both" !!!!!

Jonners

[Mitch K]

Bungay's "The Most Dangerous Enemy" describes how Squadron Leader Ralph Sorley formulated the eight-gun hypothesis: an estimate of how much damage it would take to destroy a bomber, that two seconds on target was about as much as could be reasonably achieved, and based on work with fixed targets, that eight rifle-calibre guns was the minimum that could deliver it.

As time on target became shorter, aircraft gained armour and so on, the arithmetic changed. The Germans reckoned it took on average 20 20mm cannon shells to shoot down a B-17. A Bf-109 carrying three cannon could put out about 30 rounds/second, so under a 1 second burst if you're a perfect marksman, just over two seconds if you have a 50% hit rate etc.

The R4M and similar were intended as individual aircraft killers: nothing is going to survive 500-odd grammes of hexogen going off inside the airframe, but the difficulty actually was hitting anything! Apparently the R4M trajectory matched that of the MK108 shells quite well, so you could fire the cannon and if you were getting hits roar off the whole lot with the reasonable expectation of getting more hits.

[GMK]

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

Jonners

Imagine if they had steerable bullets....http://www.engadget.com/2015/04/27/darpas-steerable-bullet-proves-it-can-hit-moving-targets/

[Giorgio N]

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

While the development of night fighters tactics was not necessarily linear, the fighter had in any case the advantages of operating under ground control and carrying a radar. The reality is that bombers often could only see the fighter when it was too late. IIRC Bomber Command during the whole war claimed little more than 1,100 enemy aircrafts shot down, considering that bomber crews claims were very hard to verify it would not be surprising if the real total was a fraction of this number. Some German night fighter units claimed more aircrafts than the whole Bomber Command. In any case the matter of range was mostly irrelevant...

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, you then probably know well (better than I do) the various approaches aimed at increasing the stopping power in modern rifles. Approaches that really started in a scientific way with the introduction of the 5.56 round for the AR15. It's IMHO a fascinating subject.

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.

I'm not sure I'd agree with the fact that it's a search that still continues. All Air Forces seem to have agreed on weapons in the 20-30 mm range, anything bigger makes no sense as any target needing more hitting power is likely to require a missile or a bomb, while anything smaller would not be effective. There are of course still differences, with some preferring Gatlings and others preferring other options.

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

Agree, in the end the search for larger calibre weapons was to increase the destructive power, it was never a matter of range. WW2 aircraft guns in any case were mostly meant to be used at ranges well below the maximum possible for each round. Aiming something from a manouvering aircraft is difficult in itself, add the use of relatively primitive aiming devices and it's clear that things are even more difficult. Having range from a radar and a reticle in a HUD makes a big difference.

Regarding the size of certain weapons, clearly they were meant to destroy bombers. No surprise that larger weapons were used by Germany and Japan as these countries had to counter continuous incursions from bombers. And it's not surprising that the Soviets added a similarly large gun to their MiG-15, as they saw the US bombers as a major threat. By the time the US started to see the potential threat of Soviet bombers, they selected a totally different weapon and went for rockets.

[JohnT]

Just got back to this today after being offline and I must say the discussion is very informative. I did know a fair bit of what has been discussed though not in as great detail.

I am still wondering about the range issue and if Me110 did sit off out of .50 range and try and drop the B-17/B-24 fleets. As has been said that soon stops once the Mustang comes along though

It just struck me as odd that there was such a discrepancy in range that seemingly it was possible in the first place. German canon shells travel further than US or Brit machine gun bullets and if they do, why?

Great discussion and references guys

[Giorgio N]

It just struck me as odd that there was such a discrepancy in range that seemingly it was possible in the first place. German canon shells travel further than US or Brit machine gun bullets and if they do, why?

Well, differences in maximum range are to be expected as here we're comparing a very large number of weapons with very different characteristics.

As said before, range depends on a number of factors and we should also understand what we mean for range. For example the land based Vickers .303 could be used in an indirect fire mode. In this mode the range was about 4,000 m. However this is not the kind of fire mode that a fighter or bomber is going to use.

The same .303 bullet when shot from an Enfield rifle (mind, MGs did not use rifle rounds but more powerful ones) can hit targets at over 2,500 m. Is this an accurate figure for the range of the rifle ? Not really, as at such distance it's very hard to hit anything accurately from even a competition tuned .303 rifle. The Enfield was a popular weapon for the 1,000 yds. competitions between the wars, so maybe 900 m is a better indication of the useful range of such a weapon. But no soldier was ever issued a specially competition prepared rifle, so it's safe to say that 600 m is the proper range at which an Enfield can be used for its intended purpose of battle rifle (although originally these were issued with sights that allowed much longer shots).

We could define as useful range the maximum distance at which our aircraft mounted weapon can throw a bullet with enough energy to cause damage and with a trajectory flat enough to allow decent accuracy with the available aiming devices. Once we accept this definition we can look at the 2 main parameters:

- Muzzle velocity: clearly, the faster the bullet and the more energy it will have for a given weight. If the bullet maintains this energy, it's possible to reach farther. Faster muzzle velocities also generally result in flatter trajectories. The velocity will depend, again for a given weight, from how much and what kind of powder is used as propellant. Of course using more and more powerful propellants is desirable but there are limitations: more power means more recoil and also a heavier weapon to withstand such power. The length of the barrel is also a limitation as different quantities of propellants are better served by different barrel lengths. A longer barrel allows higher velocities, but again this means more weight. Weight is of paramount importance in any aircraft, a compromise must be reached. Higher velocities also cause higher wear on the barrels.

For these reasons, early cannons had relatively small muzzle velocities, for example the MG-FF only achived 550/590 m/sec. The .303 MGs had velocities around 850 m/sec, much faster. The later MG151, using the same round of the MG-FF added 400 mm of barrel length and achieved velocities of 710 m/sec, making this a far longer ranged weapon than its predecessor.

- The capability of the bullet to retain its energy. Bullets are not created equal, early cannon rounds for example were not particularly streamlined and tended to lose energy quite fast. Now this may not matter in terms of destructive power as the explosive content makes up for the lost kinetik energy however it matters in terms of trajectory. If the bullet loses velocity too fast, the trajectory will not be flat enough to accurately hit at a certain range.

Weight of course also has an impact: heavier bullets will retain energy better then lighter ones, however they will also less flat trajectories. At the same time external factors are likely to influence more the lighter bullets (wind for example). There are in any case limits to the velocity that can be given to a certain weight, as shown above. Increasing the weight is an option but one that can't always be exploited. Better bullets design is the best solution.

Combining the two factors above, it's possible to see how some MGs can outrange some cannons while cannons can potentially outrange MGs: more power, higher velocities and a heavier bullet allow longer range. At the same time it's not always possible to achieve the velocity/bullet weight desired because of considerations of weight of the weapon and its assembly. Considering that in any case aircraft mounted weapons were never meant to esploit their full potential range because of aiming problems, it becomes clear that other factors were more important. Rate of fire for example is very important for air-to-air combat as a high RoF gives more chances of hitting a manouvering target. Again RoF affects the weight of the weapon, heavier calibre weapons will have to accept lower RoFs. For the destruction of bombers, heavier calibre weapons may be more desireable as the larger explosive content can be more effective on the structure of large aircrafts while the slow speed ot the bomber makes RoF less important. The extreme representatives of this concept are the large antiship guns mounted on some types (some B-25 versions or the Mosquito FB.XVIII) that had low RoFs but very large shells.

Edited May 28, 2015 by Giorgio N

[Mitch K]

I'm not sure I'd agree with the fact that it's a search that still continues. All Air Forces seem to have agreed on weapons in the 20-30 mm range, anything bigger makes no sense as any target needing more hitting power is likely to require a missile or a bomb, while anything smaller would not be effective. There are of course still differences, with some preferring Gatlings and others preferring other options.

e

I take your point, but the weapons have rates of fire varying by a factor of about 4, projectile masses (and hence explosive load) by a factor of about the same and roughly threefold variation in muzzle energy. This is still a pretty big variation. At the end of the day the gun has become somewhat a "weapon of last resort", rather than the only air to air game in town, as per WW2.

[XV107]

Machine guns tended to have a devastating effect on members of the clergy.

Cannons, on the other hand....

...are well explained in G F Wallace's Guns of the RAF. Wallace was involved in aircraft armament (which leads to a certain amount of opinion and assertion when he talks about certain projects); and Tony Williams - as will be known by many on here - knows his flaming onions (sorry, will fetch my coat...) when it comes to MG vs Cannon and the ammo types, etc, etc, on his site Military Guns and Ammunition

Colin Sinnott also covers the issue in his book The RAF and Aircraft Design: Air Staff Operational Requirements (a good book, but a bit pricey even in paperback, and thus worth the old inter-library loan route).

[old thumper]

While the development of night fighters tactics was not necessarily linear, the fighter had in any case the advantages of operating under ground control and carrying a radar. The reality is that bombers often could only see the fighter when it was too late. IIRC Bomber Command during the whole war claimed little more than 1,100 enemy aircrafts shot down, considering that bomber crews claims were very hard to verify it would not be surprising if the real total was a fraction of this number. Some German night fighter units claimed more aircrafts than the whole Bomber Command. In any case the matter of range was mostly irrelevant...

We all know that both RAF and German night fighters were directed by radar but radar did not enable the night fighter pilot to see his target before being spotted himself, neither did it ensure the night fighter pilot would actually find his target. The idea of upward firing guns on night fighters was so they could approach unseen and get to within an effective range to take aim without being shot at.

[Giorgio N]

I take your point, but the weapons have rates of fire varying by a factor of about 4, projectile masses (and hence explosive load) by a factor of about the same and roughly threefold variation in muzzle energy. This is still a pretty big variation. At the end of the day the gun has become somewhat a "weapon of last resort", rather than the only air to air game in town, as per WW2.

Do these factors actually vary by that much today ?

The rate of fire must be considered carefully as here Gatlings have a huge advantage while other guns used today all seems to be in the 1,500-1,700 rpm range. In any case, Gatlings are disadvantaged in terms of reaction times as the gun takes a while to spool up to speed, while revolver guns achieve the top RoF immediately. The result is that the amoung of bullets shot in a typical short burst is pretty much the same between the two systems.

In terms of velocity, the Russian GSh-301 is slowest at 860 m/sec, all the others however seem to be in the 1,000-1,100 m/sec range. The previous GSh-23 gun also had a relatively small velocity, guess this is not considered a problem.

We all know that both RAF and German night fighters were directed by radar but radar did not enable the night fighter pilot to see his target before being spotted himself, neither did it ensure the night fighter pilot would actually find his target. The idea of upward firing guns on night fighters was so they could approach unseen and get to within an effective range to take aim without being shot at.

The problem of night fighters was not much of being spotted by the bombers, but was that they were spotted as soon as they opened fire and this allowed the bomber crew to react. The Schrage Musik system allowed the fighters to operate below the tail RWR system, more important than operating out of eyesight. Also allowed to fire without being seen but most importantly allowed an attack profile that gave the fighter pilots more time to aim at the bomber, making attacks more succesful. At the same time, this installation was not universal and many night fighter operated very efficiently without oblique guns.

The reality of air combat has most often been that the pilot and crew of the aircraft shot down never even saw the attacker. Not only in WW2 as many reports of shot down crews in Vietnam mentioned the very same thing

Edited May 29, 2015 by Giorgio N

[Mitch K]

Do these factors actually vary by that much today ?

Being a sad anorak, I did the sums . Yes, they do.

[Jon Kunac-Tabinor]

I think we should return to the days of rather more sporting behaviour.

Yes - a Mauser C96 "Broomhandle", vs a decent Purdey 20 Bore side by side. A few hurled insults too. Then a salute and back to the aerodrome for Tea & cakes / Schnapps & torte / Café & madeleines ( delete as applicable)

Jonners - well it IS Friday...

[dfqweofekwpeweiop4]

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?

I'm sure it's been pretty much been covered but I would say Kinetic Energy has something to do with it. Without knowing all the facts and figures, if we think of higher velocity cannons such as the MG151 and Hispano, it could be a case of the Kinetic energy of the 20mm rounds they fired was more than the Kinetic energy of smaller MG bullets, therefore the cannons could penetrate the aluminium skin on the bomber at greater ranges than the MG's bullets would penetrate the fighter's aluminium skin.

If I was a WW2 fighter pilot, I think I'd want a mixed armament of 20mm cannons and MG's (50 cal preferably!), like the E wing Spitfires of Fw190's. That way you have a decent chance of damaging or destroying any type of aircraft.

thanks

Mike

[Truro Model Builder]

What I always found interesting was that the standard armament of the P-51 (six 0.5in Brownings) was carried over to the early jets, such as the F-86 that fought in Korea. Now compare that to the MiG-15's armament (two 23mm and one 37mm cannon) and it seems quite a disparity. Of course the Browning had a much greater rate of fire and the F-86 carried more armament, but when the US Navy had standardised on 20mm weapons and the RAF were designing 30mm ADENs into the Hunter and the Swift it is -to me, at least- remarkable that the USAF were still relying on smaller calibre weapons for their fighters.

[Slater]

I believe the F-86 had it's design genesis in the 1940's when machine gun armament was pretty much standard. Late variants of the F-86 did have 20mm weapons (IIRC).

[Jon Kunac-Tabinor]

I believe the F-86 had it's design genesis in the 1940's when machine gun armament was pretty much standard. Late variants of the F-86 did have 20mm weapons (IIRC).

And they trialled cannon armed F86s in Korea with Project Gunval, but hit with problems over exhaust gasses I believe. The H had 20mms, as did the K.

Jonners

[Slater]

Some technical details on Gunval (for anyone interested):

http://www.dtic.mil/dtic/tr/fulltext/u2/056763.pdf

[stevehnz]

Sorry if this has been covered before, but I've long mused on the difference to fighter command if the RAF had not been so wedded to the .303 cartridge early on in the war but had maybe instead adopted the .5 Vickers cartridge, as the Italians & Japanese did, the Italians in the Breda-SAFAT gun & the Japanese in their Ho-103 gun, a modified Browning M2. I did work thru the math some years ago, but the Vickers .5 fired a much heavier round at similar velocity to the .303 with much more effective incendiary & explosive rounds. The kinectic energy was similarly enhanced & the RAFs earlier findings of the effectiveness of a .5 weapon, Vickers or Browning against the .303 were not born out in the BoB where a gun with more effective striking power was sadly lacking. The Italians tended to hamstring their fighters by only fitting 2 of the 12.7 Breda-SAFAT weapons, (.5 Vickers derivative) Likewise the Japanese but they also had a 20mm weapon earlier in the conflict to compensate for this. Nevertheless, many allied aircraft succumbed to two 12.7s, Imagine how much more effective a Hurricane or Spitifire with 4 or 6 .5 Vickers would have been against Luftwaffe bombers in 1940.

Steve.

[old thumper]

I just think this is one of those things that will always be argued over. That's me over and out.

[JohnT]

Going back to the range issue I wonder in the light of the above comments whether what authors are referring to when they write about canon armed fighters hanging back out of range of machine gun armed bombers and shooting them at will is more to do with what ranges pilots thought their and the opposition weapons were effective/ ineffective as opposed to actual ranges. In other words it's down to a belief conceived in the heat of combat rather than an actuality?

[Sebastien]

What I always found interesting was that the standard armament of the P-51 (six 0.5in Brownings) was carried over to the early jets, such as the F-86 that fought in Korea. Now compare that to the MiG-15's armament (two 23mm and one 37mm cannon) and it seems quite a disparity. Of course the Browning had a much greater rate of fire and the F-86 carried more armament, but when the US Navy had standardised on 20mm weapons and the RAF were designing 30mm ADENs into the Hunter and the Swift it is -to me, at least- remarkable that the USAF were still relying on smaller calibre weapons for their fighters.

Are you sure no French general was involved in designing the F-86 armament?

Sebastien

[hacker]

It was that the only opposition the Sabre had was another fighter but that soon changed when it became apparent the Russians had back engineered the B-29 from the few that came into their possession. Then they realize that the 50s couldn't knock down bombers quickly (the same problem the Luftwaffe had). So the USAF began gunning up their aircraft and or using 2.5 inch rockets. The whole thing is interesting isn't it?

[Giorgio N]

Sorry if this has been covered before, but I've long mused on the difference to fighter command if the RAF had not been so wedded to the .303 cartridge early on in the war but had maybe instead adopted the .5 Vickers cartridge, as the Italians & Japanese did, the Italians in the Breda-SAFAT gun & the Japanese in their Ho-103 gun, a modified Browning M2. I did work thru the math some years ago, but the Vickers .5 fired a much heavier round at similar velocity to the .303 with much more effective incendiary & explosive rounds. The kinectic energy was similarly enhanced & the RAFs earlier findings of the effectiveness of a .5 weapon, Vickers or Browning against the .303 were not born out in the BoB where a gun with more effective striking power was sadly lacking. The Italians tended to hamstring their fighters by only fitting 2 of the 12.7 Breda-SAFAT weapons, (.5 Vickers derivative) Likewise the Japanese but they also had a 20mm weapon earlier in the conflict to compensate for this. Nevertheless, many allied aircraft succumbed to two 12.7s, Imagine how much more effective a Hurricane or Spitifire with 4 or 6 .5 Vickers would have been against Luftwaffe bombers in 1940.

Steve.

A comment on the Italian fighters armament: the Air Force considered a 0.5" weapon to be twice as effective as a rifle calibre weapon and a 20mm gun twice as effective as a .5" weapon. The armament of 2 X 0.5" machine guns was considered a compromise between the search for some firepower and the weight of the guns and ammunition. The chronical lack of power of late '30s Italian fighters meant that a lot of equipment had to be sacrificed and this included reducing the number of guns (and radio equipment and a few other things). A number of types were actually designed for heavier armament but this was rarely if ever installed.

As said before, a heavier armament has advantages but it also affects the performances of the aircraft. A compromise must be reached, Fighter Command believed that the disadvantages of the 0.5" outweighted the advantages

It was that the only opposition the Sabre had was another fighter but that soon changed when it became apparent the Russians had back engineered the B-29 from the few that came into their possession. Then they realize that the 50s couldn't knock down bombers quickly (the same problem the Luftwaffe had). So the USAF began gunning up their aircraft and or using 2.5 inch rockets. The whole thing is interesting isn't it?

The introduction of 20mm guns on USAF aircrafts was not really related to the appearance of Soviet bombers as the USAF had worked to introduce this weapon for years. A number of USAF types actually had used 20mm guns during the war, notably the P-38 and the P-61. The problem was that US built Hispano guns suffered from reliability issue and this limited their use. It was only with the MG213 derived M39 that the USAF finally decided to arm all their fighters with 20mm guns, although the M61 entered service only a few years later and then became the standard on all US fighters

The introduction of the rockets in types like the F-86D, F-89D and F-94C was indeed related to the Soviet bomber threat, however not directly to the need of fknocking out larger targets. It was the increase of the speed of the bombers that required a complete rethinking of the fighter armament: with the potential threat of jet bombers capable of high subsonic speed, the fighters of the day did not have the speed advantage required to manouver into position for an attack with guns and the only solution was to send the fighter on an interception course that would have allowed one single firing pass. A salvo of rockets allowed a higher probability of destroying the intruder during this single firing pass. Very soon the fighter started to regain its speed advantage and with the advent of the missile the days of the rocket as an AA weapon were pretty much over.

Edited June 15, 2015 by Giorgio N

[Truro Model Builder]

It was that the only opposition the Sabre had was another fighter but that soon changed when it became apparent the Russians had back engineered the B-29 from the few that came into their possession. Then they realize that the 50s couldn't knock down bombers quickly (the same problem the Luftwaffe had). So the USAF began gunning up their aircraft and or using 2.5 inch rockets. The whole thing is interesting isn't it?

I can only imagine what effect four 30mm ADENs would have on a pressurised aircraft. Not pretty.

[Selwyn]

I can only imagine what effect four 30mm ADENs would have on a pressurised aircraft. Not pretty.

They work pretty well on unpressurised aircraft as well!

Selwyn