The Italian Air Force was unusual in changing very early from RCMGs to HMGs, but rather threw away the lead this might have given them at the start of the war by typically fitting very few of
them. As already stated, the Italians adopted the 12.7 x 81SR Vickers cartridge and produced two of their own weapons in this calibre, the Breda-SAFAT and the Scotti, the former being far more important and numerous. They also produced prototypes of two 20mm guns, the Breda CL20 and another design by Scotti, but neither saw service, the MG 151/20 being used instead.
When Italy entered the war in 1940, the main fighters were the FIAT CR32 and CR42 Falco biplanes, being supplemented by the FIAT G.50 Freccia and Macchi MC.200 Saetta monoplanes. The usual armament of all these aircraft consisted of two 12.7mm Breda-SAFATs in the traditional cowling-mounted and synchronised installations, although in some versions these were supplemented by another pair of wing-mounted guns, usually RCMGs. Even the first of the new inline-engined high-performance fighters, the MC.202 Veltro and Reggiane RE.2001 Falco //, were no better equipped. The only adequately armed Italian fighters were the modified MC.205V, with two 12.7s and two MG 151 /20s, and the FIAT G.55 Centauro which had two 12.7s and three MG 151s, but these were too late to have any impact before Italy's surrender in 1943.
Italian bombers were generally equipped with flexibly mounted defensive weapons, usually RCMGs, but some had one 12.7mm gun in a dorsal turret. The Savoia-Marchetti SM79 Sparviero and SM84 torpedo bomber were the only ones to feature more than one HMG, but even then had only three or four, most of which were flexibly mounted.
Like the British, the French had little time for HMGs, jumping straight from RCMGs to cannon. Hotchkiss did produce a belt-fed aircraft version of their 13.2mm HMG which was capable of 600 rpm, but its use is uncertain. Like the Germans, the French first experimented with large and powerful cannon, among them the 25mm Hotchkiss, a
gas-operated gun weighing 70kg but initially firing at only 180 rpm from a ten-round clip. By the late 1930s the performance had improved to 300 rpm from a thirty-five-round magazine and a visiting US delegation showed some interest, but the French claimed that it was secret and refused to sell. The first French cannon to see service, however, were versions of the Oerlikon FFS already described, adapted for engine mounting and made by Hispano-Suiza as the Types 7 and 9. Early inline-engined aircraft such as the Dewoitine D.501/510 and Morane-Saulnier MS405 carried one of these together with a pair of RCMGs.
The low rate of fire of the Oerlikon guns (around 400 rpm) was considered unsatisfactory, and as a result a much better weapon emerged (designed by a Swiss, Marc Birkigt), the famous 20mm Hispano-Suiza HS 404. This was used in the Dewoitine D.520 and MS406, but again only one engine-mounted cannon was fitted, supplemented by four or two RCMGs respectively. It appeared that Birkigt initially tried mounting the gun rigidly as had been achieved with the low-recoiling HS 7 and 9. However, the HS 404 s action resulted in a much sharper recoil blow so a recoiling mounting had to be devised, complicating the ammunition feed from the drum, which needed to remain stationary as its size and weight precluded its being rattled to and fro ten times per second.
The French were rightly proud of the HS 404 and were intending to rely increasingly on it had they remained in the war. Some versions of the radial-engined Bloch MB-152 and the MB-155 carried two wing-mounted cannon. It was even fitted as a defensive weapon in bombers such as the Farman (Centre) NC 223 and Liore-et-Olivier LeO 451. While initial French interest was focused on a version firing a powerful 23 x 122 round (the HS 406), only the 20mm saw service. The gun even saw German service. Some versions of the Do 24, built on captured Dutch production lines, were equipped with the HS 404 in the dorsal cupola, and the gun was also used as an A A weapon.
Oerlikon were not the only Swiss company producing aircraft cannon. The Swiss adopted a version of the French MS406 fighter as the D-3800 series but fitted their own engine-mounted cannon, the recoil-operated FMK38, designed around a
high-velocity 20 X 139 cartridge which was the precursor of the current Oerlikon KAD round. Rather bizarrely, the gun was also fitted to the C-35 biplane, thus combining an ancient aircraft concept with one of the most powerful 20mm aircraft guns ever to see service.
Finland produced a range of heavy weapons including the 12.7mm LKk/42, four of which were mounted in the cowling of the VL Myrsky fighter, in service between 1944 and 1947. Little information seems to have survived about this weapon, except that it was belt-fed and unpopular because of inaccuracy problems caused by a tendency to overheat. Cannon were also produced in Finland by Lahti, using his own 20X113 ammunition, but despite some reports that these saw airborne service in the Russo-Finnish wars it appears that they were only used by the navy, fitted to patrol boats. The Finns certainly used a wide variety of equipment including some 12.7mm Brownings converted for aircraft, 20mm MG-FF, MG 151 and ShVAK, and according to one report some Oerlikon FFL. However, it is difficult to determine which aircraft used the guns, as it appears that individual planes received a variety of armament fittings, depending, presumably, on whatever was to hand.
The Danish firm Madsen also produced cannon which saw action, albeit mostly in German hands and in the A A rather than aircraft version. The gun was available in both 20mm and 23mm calibres, although it appears that only the former saw service despite considerable pre-war promotion of the 23mm, which was featured as the proposed armament of several aircraft of various nations. Madsen also produced a 'heavy" machine gun (to stretch the definition) which only saw service with Argentina, the 11.35mm. This was another attempt to increase the hitting power of air weapons while keeping weight and dimensions to a minimum. The little 11.35 x 62 cartridge had the same overall length as a .30'06 or 7.9mm round, and at 10.5kg the gun weighed the same as rifle-calibre weapons.
23 mm Madsen (BuOrd, USN)
57mm Bofors m/47 (BuOrd, USN)
Sweden also used a version of the Browning HMG chambered for the 13.2x99 Hotchkiss round, a similar weapon to the UN 13mm Type 3. Known as the m/39A, this was later converted to 12.7x99. At the other end of the heavy weapon spectrum, Bofors produced the 57mm m/47 airborne anti-shipping gun which was fitted to the SAAB T18B twin-engined attack bomber, but this was a post-war development.
Among the largest installations to see service was carried by the Italian Piaggio P. 108A four-engined heavy bomber. This was fitted with an old naval gun of 4" (102mm) calibre for anti-shipping purposes (not the Ansaldo 90/53 often mentioned; that was a high-velocity 90mm A A gun), but the gun was manually loaded.
The Second World War:
experience and conclusions
The Second World War commenced with RCMGs dominating aircraft armament, supplemented by a few HMGs and low-powered 20mm cannon. It soon became evident that aircraft could be protected reasonably well against RCMG fire, which led to a rapid increase in the use of HMGs and the introduction of more powerful and faster-firing 20mm guns. In the two nations which had to deal with massive onslaughts by heavy bombers -Germany and Japan - there was a growing interest in guns of 30mm or more by the end of the war.
Not all nations were willing to add armour to their aircraft. The Italians were slow to respond to the need for this and the Japanese Navy scorned it until the latter stages of the war, both unwilling to compromise the exceptional agility of their aircraft (and in the case of Japanese aircraft, their amazing range). Soviet fighters never had adequate protection, although ground-attack aircraft were heavily armoured. In contrast, the British, Germans and Americans rapidly adopted self-sealing tanks and armour protection, at least for pilots.
Bomber defensive armament saw much less development as it was much easier to bolt a bigger gun onto an existing fighter than it was for a bomber to be modified to accommodate a much larger turret. RCMGs were virtually standard at the beginning of the war, with rarely more than half-a-dozen guns carried. These were upgraded to HMGs in most air forces during the war, with the exception of the RAF which had planned no production of
World War 2 fighter gun cartridges (from left to right): .50" Browning (12.7 X 99), Hispano HS 404/AN-M2 (20 x 110), 37mm M41M10 (37 x 145R), IJN 13mm Type 3 (13.2 x 99), IJN Type 99-1 (20 x 72RB), IJN Type 99-2 (20 x 101RB), 12.7mm Breda- SA FAT I ScottilIJA Ho-103 (12.7 x 81 SR), IJA Ho-5 (20 x 94), IJA Ho-IIHo-3 (20 x 125), 12.7mm Beresin (12.7 x 108), ShVAK (20 x 99R), MG 131 (13 x 64B- | also IJN 13mm Type 2), MG 151 (15 x 96), MG-FF (20 x 80RB), MG 151/20 (20 X 82), MG 204 (20 x 105), MK 103 (30 x 184B)
HMGs. Later bomber designs in Germany, Japan and the Soviet Union featured defensive 20mm guns. The RAF and USAAF were handicapped in following suit by the great length of the unwieldy Hispano which they had both adopted as their standard cannon.
An aspect of Second World War armament which attracts little attention is that which is currently known as combat persistence - the ability to keep on fighting, which apart from aircraft fuel tankage was then very much connected with ammunition magazine capacity. During the Battle of Britain, the Spitfire I had a capacity of 300 rounds per gun, giving about sixteen seconds" firing (the Hurricane carried slightly more). Their main opponent, the Bf 109E, was in a curious position, in that the two MG-FF had only 60 rpg, around seven seconds* worth, but the two synchronised RCMGs had no less than 1,000 rounds each, enough for a whole minute s firing (this was reduced to 500 rpg in later versions with an engine-mounted cannon). On the other hand, sixty seconds of fire from two RCMGs delivered only the same weight of fire as fifteen seconds from the British planes* eight-gun installations.
The Germans stayed with Trommel (drum)
World War 2 airborne ground-attack cartridges (left to right): ShVAK (20 x 99R), VYa (23 x 152B; this is actually the postwar ZU but the shape was almost identical), MK 101/MK 103 (30 x 184B; N.B. drawing in Appendix 3 shows the H art kern projectile), 37mm M4/M10 (37 x 145R), 3.7cm BK 3.7 (37 x 263 B), 40mm Vickers Class S (40 x 158R), 5cm BK 5 (50 x 419 R), 6pdr Mo/ins (57 x 441R). The NS-37 is shown in Appendix 3.
Typical fighter armament fits, with an approximate comparison of their effectiveness, are shown below:
Year Aircraft Weapons KG RPS KPS
1940 Hawker Hurricane I 8 x 7.7mm Browning 80 160 1.8
1940 Messerschmitt Bf 109E-3 2 x 20mm MG-FF 52 17 2.0
1941 MiG-3 lx 12.7mm UBS 25 15 0.8
1941 Focke-Wulf Fw 190A-2 2 x 20mm MG 151 84 23 2.6
1941 Supermarine Spitfire VB 2 x 20mm Hispano II 100 20 2.6
4 x 7.7mm Browning 40 80 0.9
1942 Mitsubishi A6M2 (Zero) 2 x 20mm Type 99-1 49 17 2.2
1942 Curtiss P-40B 2 x 12.7mm Browning 58 15 0.7
2 x 7.6mm Browning 20 40 0.4
1944 Lavochkin La-7 3 x 20mm Beresin 75 40 3.9
1944 Hawker Tempest Mk V 4 x 20mm Hispano V 168 50 6.5
1944 Nakajima Ki-84-lb 4 x 20mm Ho-5 144 57 6.8
1944 North American P-51D 6 x 12.7mm Browning 174 85 3.9
1944 Messerschmitt Me 262A-1 4 x 30mm MK 108 240 43 14.2
KG = total weight of gun installation in kilograms
RPS = number of rounds fired per second
KPS = total weight in kilograms of projectiles fired per second magazines for all applications of the MG-FF apart from the GZ 1-FF belt-drive, which could handle up to 2,000 rounds per gun. Later work raised the drum capacity to ninety rounds (the T 90-FF) without increasing the diameter, but this saw little service, as did other sizes of drum and magazine, varying from fifteen to a hundred rounds. The ammunition capacity of other Luftwaffe weapons varied considerably. The Bf 109G carried 150 rounds for its MG 151/20 (just over twelve seconds) and 300 rpg for its two synchronised MG 131 (twenty seconds) while the Fw 190D carried 250 rpg for each of its two MG 151/20 (twenty-one seconds) and 475 rpg for the two MG 131 (thirty-two seconds). Installation of the engine-mounted MK 108 in later versions of the Bf 109G reduced the capacity to sixty rounds (six seconds), although each shell had far more hitting power. The Me 262 had 100 rpg for two of its MK 108s, 80 rpg for the other two.
The first 20mm Hispano guns also used a sixty-round drum (giving only six seconds1 firing) which accounts for the RAF s keenness to introduce belt feeding. Fighter installations of belt-fed Hispanos typically provided 120-150 rpg (twelve to fifteen seconds), although the Beaufighter carried 240-283 rpg, providing almost half a minute's firing. These figures proved adequate in practice. Analysis of camera-gun film revealed that an average of seventeen rounds of 20mm were fired per burst, with three to five bursts per combat, at intervals of between three and ten seconds. Ammunition capacity for the American aircraft's .50" calibre guns also
varied, from 240-280 rpg in F4F, P-40 and most P-47 installations (around twenty seconds) to 400-500 rpg in P-38 and later P-47s (thirty to forty seconds).
Italian fighters typically carried 300-400 rounds of 12.7mm ammunition (twenty-five to thirty-five seconds) and an equally generous 200-250 rpg (seventeen to twenty-one seconds) for the MG 151/20 cannon fitted later on. Soviet fighters generally carried 120-200 20mm rounds (nine to fifteen seconds) and around 250-300 rpg for the 12.7mm guns (fifteen to eighteen seconds). Information about Japanese installations is less readily available, but RCMG capacity was typically 500 rpg, HMG 250 rpg and 20mm cannon, initially 50-60 rpg with drum feed, rose to 100-125 rpg when belt feed was introduced.
An interesting detail concerns the use of tracer ammunition. This was often favoured by bomber crews as they felt that it distracted attacking fighter pilots; the US Ordnance Department even developed a special .50" tracer, the M21 'Headlight1, which was three times more visible than usual from the front, and good results were reported. On the other hand, USAAF fighter units which did not use tracers reportedly achieved far more kills and suffered fewer losses than tracer-equipped units, presumably because the use of tracers warned enemy fighter pilots that they were being attacked.
In all cases, ammunition capacity for bomber defensive guns was considerable. The Avro Lancaster had an average of 1,750 rpg of RCMG rounds, enough for one and a half minutes' continuous firing. Operational Research revealed that the average expenditure per mission for mid-upper turrets in RAF aircraft was 235 rounds, while even for the rear gunner a total of 2,000 rounds was adequate for 99% of missions, in comparison with a capacity of up to 10,000 rounds.
The need for defensive fire for the RAF s night bombers was questionable as the main value of gunners was to give warning of approaching night-fighters early enough for the pilot to take the violent evasive action which gave the best chance of survival. Some 90% of Lancaster sorties were made without any contact being made with enemy fighters; of the 10% which were attacked, half were shot down despite their defensive armament. The
Mosquito bomber had no guns, relying on speed and stealth to evade the fighters, and had a loss rate one-twentieth that of the Lancaster.
American heavy bombers typically carried an average of 500 rpg of .50" ammunition (the quantity per gun varied), but sometimes ran short of ammunition during their bitterly contested daylight raids. Despite the power of their HMGs the advantage still lay with the attacking fighters, against which the only effective defence proved to be escort fighters.
The war demonstrated that it was not the technically advanced concepts which achieved the most. The most successful weapons were those which were the most practical, in terms of being fully developed, easy to make and reliable in service. A good example of this is provided by a comparison between the 20mm Hispano, which was at first rather large and heavy for its class, and the Mauser MG 151. When the first MG 151/20 was recovered by the British, they were impressed by its compactness, light weight and high rate of fire, and considered copying it. However, on more detailed examination of the beautifully engineered rotary-locking bolt mechanism, British industrialists concluded that their equipment and workers were not capable of manufacturing it. Efforts were accordingly concentrated on improving the relatively simple Hispano instead, and the resulting Mark V was a close match for the Mauser.
Another interesting contrast is provided between the weapons turned out by the British, Germans and Americans on one hand, and the Soviets and Japanese on the other. The Soviet and Japanese guns commonly had a higher performance (in terms of rate of fire) and a significantly lighter weight than equivalent Western weapons, a tradition that the Russians have continued to this day. The Soviet 12.7mm Beresin, 20mm ShVAK and 20mm B-20, and the Japanese 12.7mm Ho-103 and 20mm Ho-5 are good examples.
How could they achieve this? It seems likely that they took a much more pragmatic attitude to weapon life than the Western nations. For example, the 20mm Hispano was initially designed for a life of 10,000 rounds. On investigation during the war, it was discovered that very few guns even managed 1,000 rounds before being destroyed in action or in a crash, and the majority never fired more than a few hundred rounds. In fact, the Hispano was later lightened but could still achieve 2,500 rounds even for the smaller components, with the main elements lasting for 5,000 rounds. A designed gun life of 500-1,000 rounds might well have permitted a much lighter construction and/or a higher rate of fire without any practical disadvantages.
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