CLICKY This is mostly post-WWII but still quite interesting (I hope it hasn't been posted before). BTW, look at how HUGE those 30 and 37 mm shells are in comparison to a 12mm round.
Punch for the Fighter. As has been mentioned (see *). In 1934 when the race began to develop fighters, the usual armament was two slow-firing (about 750 rounds per minute)rifle-caliber machine guns. Obviously their weight of fire would be insufficient to knock down the sort of bombers to be expected at the end of the decade, and in each of the major nations work began on heavier armaments for fighters. By 1939 fighters were in service with three basic types of guns: the fast-firing rifle-caliber machine gun, the slower firing heavy machine gun, and the shell firing cannon. At the outbreak of the Second World War all operational fighter aircraft carried rifle-caliber machine guns as all or part of their armament: the American browning .300 inch (7.62 mm) or the similar licence-produced British .303 (7.7 mm), the french MAC 7.5-mm, the German Rheinmetall Borsig MG 17 of 7.9 mm, the Italian breda SAFAT of 7.7 mm, the Polish Wzor of 7.7 mm, the Japanese Type 89 of 7.7 mm and the Russian ShKAS of 7.62 mm. Of these the ShKAS (Shpitalny Komaritsky Aviatsionny Skorostrelnu ? fast-firing aircraft gun) was, as has been mentioned, the best all-rounder; it had a rate of fire of 1,800 rounds per minute with a muzzle velocity of over 2,700 feet per second,all for a weight of 22 pounds. Prior to the war three nations had put into service fighters equipped with .5-inch (12.7mm) heavy machine guns; the U.S.A. with the .5 Browning, italy with the 12.7-mm Breda SAFAT and Russia with the 12.7-mm UBS. Of these the Russian weapon was again the best. The UBS (Universalny Berezina Skorostreny-Berezina universal fast-firing gun) had a rate of fire of 900 rounds per minute with a muzzle velocity of over 2,800 feet per second, for a weight of just over 47 pounds. Finally ther were the shell-firing cannon, of 20-mm caliber in each case(the arbitrary division between a machine gun and a cannon is that the latter has a caliber of 15mm or greater). At the beginning of the war thier were three types in service: the German Oerlikon, the French Hispano Suiza and the Russian ShVAK. Later the Oerlikon was manufactured under licence in Japan, and the Hispano was produced in Britain and , subsequently, in the U.S.A. With a weight of only 60 pounds the Oerlikon MG FF was the lightest of the cannon, while the 7.7-ounce round it fired was the heaviest of the three. On the other hand it?s rate of fire of only 350 rounds per minute and it?s low muzzle velocity of 1,950 feet per second meant that the german weapon had the lowest performance in these respects. The Hispano Suiza cannon of the early war period was the heaviest of the weapons at 109 pounds; it fired 4.4-ounce rounds at a rate of 700 per minute and a muzzle velocity of 2,820 feet per second, which meant that this weapon delivered a weight of fire about twice as great as that of the Oerlikon. The Russian ShVAK (Shpitalny Vladimirov Aviatsionnaya Krupno Kaliberaya ? large caliber aircraft gun) was different again, with a weight of 92 pounds and firing light 3.5-ounce rounds at a rate of 800 per minute with a muzzle velocity of 2,820 feet per second. The Oerlikon and the early Hispano Suiza cannon were fed from drum magazines with a capacity of only 60 rounds; the ShVAK was belt fed. During the first year of the war the trend was for aircraft to carry self-sealing tanks and armour protection for the crew positions, with the result that the effectiveness of fighters armed only with rifle-caliber machine guns was greatly reduced. The Royal Air Force had decided before the war that the Hispano Suiza was the best available cannon for use against armoured aircraft, as indeed it was. With it?s heavy projectile and very high muzzle velocity, the French cannon had a penetrative power about 50% greater than the ShVAK and double that of the Oerlikon. During the summer of 1940 there was a struggle to get the Hispano operational in the Spitfires and Hurricanes. But the Hispano had originally been designed for mounting along the top of the engine of the fighter, so that the latters weight could absorb the recoil forces; it did not take kindly to being pushed into less-rigid mountings out in the wings, which was the only place where there was room for it on the British single-engined fighters. The result was that the early career of the Hispano in the Royal Air Force was a sad tale of frequent stoppages and failures, as the cannon tried to shake apart itself and its feed system during firing. When in the spring of 1941 the problems of the Hispano were finally sorted out, the Royal Air Force possessed a very reliable and hard-hitting weapon which was to serve it well for the remainder of the war. In Germany the limitation of the Oerlikon were well appreciated before the war, but the wepaon had to serve until the more effective Mauser MG 151/20 was ready for service. The Mauser 20-mm cannon had a rate of fire of 750 rounds per minute and a muzzle velocity of 2,500 feet per second. Like the Russian ShVAK it fired a 3.5-ounce shell, and it was broadly comparable in terms of weight and because it too used belt feeding. The Mauser weighed a bit less and fired a bit faster than the Hispano, but it?s penetrative ability was considerably less. Meanwhile, far away in the U.S.A., there had been a progressive up-gunning of the rather feebly armed fighters which had been in service in that country?s air force at the beginning of the war. The armament fitted to new fighters moved up through various combinations of .3 and .5-inch machine guns and 20-mm and even 37-mm cannon, until by the early part of 1942 it began to settle at four, six, and eight .5-inch Browning heavy machine guns. Although the .5-ince Browning lacked the penetrative power of the 20-mm cannon the U.S. Army Ordinace department believed, rightly as it turned out, that this weapon would be perfectly adequate against the enemy aircraft likely encountered during the second world war. The Germans never armoured their aircraft to withstand .5-inch rounds, and the Japanese certainly did not. But incase their hunce was wrong the Americans played it both ways and put the Hispano cannon into limited production; known as the M-2, the licence-built weapon fitted into a small proportion of their fighters. By the middle of the war all of the combatant nations had begun or completed the replacement of the rifle-caliber weapons in their fighters with cannon or heavy machine guns. The Japanese produced a near copy of the .5 Browning as the 12.7mm type 1 machine gun, the German Rheinmetall Borsig company produced the 13-mm MG 131 which fired a lighter round at a lower muzzle velocity then the Browning, though with a slightly higher rate of fire; the Russians gradually replaced the rifle-caliber ShKAS gun with the UBS; and the Royal Air Force belatedly replaced the .303-inch machine gun in its Spitfires with .5-inch brownings, when it was finally able to get hold of these precious weapons. Against fighters or medium bombers carrying normal amounts of armour the fire power of the .5 inch heavy machine gun was adequate and that of the 20-mm cannon was ample. The trouble was, as the Germans and the Japanese began to descover from the latter half of 1942, that these weapons simply weren't powerful enough against the tough american B-17 and B-24 heavy bombers. For example, the Focke-wulf Fw 190-A3 carried an armament of two Oerlikon Mg FF and two Mauser MG 151/20 20-mm cannon, and two rifle-caliber machine guns; during a three second burst these guns loosed off 130 rounds each of 20mm and 7.9 mm ammunition. On the average, twenty hits of 20mm were required to bring down one of the American heavy bombers (it must be stressed that this was the average figure; some bombers were shot down with less hits,some returned with more.) unless they scored a lucky hit on the pilot or some other vital part, the rifle-caliber weapons were of little value in such an engagement. During the analysis of air-to-air combat films, Luftwaffe armament experts found that the average fighter pilot was hitting a bomber with only about 2% of the aimed rounds that were fired. Thus, to obtain the twenty hits required to shoot down the heavy bomber, one thousand rounds of 20-mm ammunition had to be aimed at it; this represented 23 seconds? firing time for the fw 190A-3, an impossibly long time if the bomber was still in formation and the fighter pilot was on the receiving end of heavy defensive fire. It was found that the majority of the heavy bombers shot down by fighters fell either to the aces, who were beating the odds and getting far more than 2% of their rounds on the target, or else the bombers had first been damaged during previous fighter attacks or from flak and forced out of formation, and were then finished off in long firing passes pressed home to short range. Dr Samuel Johnson once assured us that when a man knows he is to be hanged in a fortnight, it concentrates his mind beautifully. By the Autumn of 1942 the Luftwaffe High Command knew that unless something was done soon they faced the prospect of having to meet large-scale daylight attacks on the German homeland, without adequately armed fighters. And the thought of that concentrated their minds beautiffuly. Fortunately for the Luftwaffe, at this time the Rheinmetall borsig company had 2 30-mm heavy cannon in an advanced state of development and one of these, the Mk 108 was chosen as the standard bomber-destroyer weapon. The Mk 108 had a high rate of fire of 660 rounds per minute, though its muzzle velocity was only 1,750 feet per second. Its 11-ounce incendiary or high explosive shell had an effect on aircraft structures which was truly devastating: against fighters or medium bombers a single hit was almost invariably sufficient to cause their destruction; against a four engined heavy bomber, three or four hits were usually enough. During 1943 the MK 108 went into action fitted the the messerscmitt Bf 109, which carried one, and the messerscmitt Bf 110 and the focke-wulf Fw 190 each of which carried two. When the Me262 jet fighter entered service in 1944 it carried the unprecedentedly heavy armament of four Mk108 guns; complete with the mountings and 360 rounds of ammunition, this battery weighed more then 1,100 pounds and could loose off a projectile weight of 96 pounds during a 3 second burst. This was far away the heaviest weight of fire possible for an operational gun-equipped fighter during the Second World War and when it struck home the effect on the victim was usually catastrophic. For all its destructive power, however, the Mk108 was not the complete answer to the Luftwaffe?s problem. It was a low velocity weapon; to cover 1,000 yards its shell took over two and a half seconds, and they dropped nearly 100 feet before they got there. Clearly this was no weapon for long-range firing against moving targets, and to use it the german pilots still had to press home their attacks to well inside the range of the bombers? defensive fire. In an attempt to knock the bombers out of formation at longer ranges, the Germans introduced a modified version of the 50-mm high velocity gun fitted to some of their tanks; with automatic loading and a new recoil system and barrel, this weapon became the BK 5 which was fitted into the Messerscmitt Me 410. The BK 5 fired shells weighing 3.5 pounds, large enough to knock down a heavy bomber with a single hit; leaving the muzzle with a velocity of 3,000 feet per second, they took just over a second to cover 1,000 yards and the gravity drop was only 24 feet. The rate of fire of only 45 rounds per minute(3 in 4 seconds) was inordinately slow, but it was felt that the weapons high velocity and destructive power would more then make up for this. The combination of the Me 410 and the BK 5 seemed to provide an ideal solution to the problem of stemming the American heavy bombers. But in war nothing stands still. By the time the new bomber destroyer was ready for action, in the spring of 1944, the American escort fighters were operating over Germany in such numbers that the slow deliberate attacks from behind the bomber formations were quite out of the question. To replace the Mk 108 as the standard German heavy cannon, the Mauser company came up with its tour de force, the magnificent MG 213. Intially produced with a caliber of 20mm, the MG 213 was later to have been built in a 30-mm version as well. The 7.4-ounce shell of the 20-mm were twice as heavy as the noraml projectile for this caliber, and the Mg 213 spewed them out at a muzzle velocity of3,300 feet per second and a rat of 1,200 per minute. The reason for this superb performance was that the weapon was fitted with a unique revolving chamber which served as both breech and part of the feed mechanism. Just to late to see action during the Second World War, the Mg 213 represented the zenith of aircraft gun design in 1945 and dominated it for more then a decade afterwards. After the war everybody copied its clever feed system which was used in the American M-39, the British Aden, the French DEFA and the Russian NR 30 cannons. In an effort to produce a really effective bomber-destroyer, the Japanese fitted 30-mm, 37-mm and even 40-mm cannon to their fighters. The 30-mm Ho 105 was an effective weapon with a muzzle velocity somewhat higher than that of the German MK 108, though its rate of fire was lower. The 37-mm Ho 23 was greatly inferior, with a rat of fire of only 120 rounds per minute. The 40-mm Ho 301 fired an unuasual type of round without a cartridge; the propellant was housed in a compartment at the rear of the projectile, and when it was fired the expanding gases impinged on the breechthrough hole cut in the rear of the round. This method had the advantage that there was no cartridge case to extract from the breech before the next round was rammed home; as a result the cannon had a rate of fire of 450 rounds per minute, which was remarkably high for a weapon of this caliber. The great disadvantage was that the weapon had a muzzle velocity of only 760 feet per second, by far the lowest of any air-to-air gun used during the conflict, and because of this its effective range was limited to about 150 yards. During the war the Japanese heavy cannon saw only limited use, and they did not make any noticeable impression in combat before it ended. please excuse any mistakes, was up rather late when i typed it.
