Shop Amazon - Create an Amazon Baby Registry

The WWII Fighter Gun Debate

The Question

The Guns

• The Name of the gun
• The type of round as, for example, 13 x 64 (36.5g). The first number is the calibre of the barrel, in millimeter. For rifled barrels this is the smallest internal diameter, and the diameter of the projectile is slightly larger.
  The second number is the length of the cartridge case, again in millimeter, with R appended for Rimmed, SR for Semi-Rimmed cartridges, RB for cartridges with reBated Rims (sometimes tables list these as RR), and B for Belted cartridge cases. Such variations in the shape of the cartridge are usually linked to the operating principle of the gun.
  The third number is the weight of the projectile in gram.
  Note that guns are usually able to fire several types of ammunition, and they were often mixed. Machinegun ammunition could be armour-piercing, tracer or incendiary, or a combination of those. For cannon high-explosive shells were also used.
• The rate of fire in rounds per minute. Muzzle velocities of course depend on the type of ammunition fired. I generally list averages, which may differ from values listed elsewhere.
• The muzzle velocity in meter per second. For those more familiar with feet: A foot is 0.3048 meter.
• The weight of the gun, in kilogram. A pound is 0.4536 kilogram.

Rifle-calibre machineguns

The best known gun of this list is the Browning M2. The origins of this weapon go back to a gun designed in 1917 for use by the infantry. The M2 version was developed for installation in aircraft in the early 1920s, and compared with earlier models its rate of fire was increased. The gun is still in use today. The British version fired rimmed .303 ammunition instead of rimless .30 ammunition.

The gas-operated French 7.5mm Darne was used in both fixed and movable installations, and its good characteristic was its high rate of fire. But because of the early French defeat its impact on the war was minimal, and after the war it quickly disappeared.

The German MG17 was derived from the Swiss Solothurn design. It was often in synchronized installations, on the engine cowlings of German fighters, and this reduced rate of fire to 1000rpm. In 1939 the Luftwaffe introduced the superior Mauser MG81, much lighter and with a high rate of fire. But this was used almost exclusively in defensive installations, because the Luftwaffe recognized that the 7.92mm calibre was obsolete as fighter armament.

The Italian Breda-SAFAT 7.7mm gun is reported to have had about the same rate of fire as the 12.7mm version, which does not seem to make much sense. If it is true, it was a rather poor weapon. Nevertheless it was fairly important in the early years of the war, used in combination with the 12.7mm version.

The Japanese Army and Navy both used uprated copies of the British Vickers, of WWI vintage, and of the the German MG 15 observer gun. Their independent production of nearly identical weapons is almost symbolic for the lack of cooperation between the two services. No country had so many different guns in use as Japan, with so many different types of ammunition. They even managed to produce three types of .303 ammunition, with rimmed, semi-rimmed and rimless cartridges!

The Army guns were the Type 89 model 1, an indigeneous drum-fed design used in flexible installations; the Type 89 model 2, a copy of the Vickers, and the Type 98, a copy of the MG15. The Navy used the Type 92, a copy of the Lewis and again used in flexible installations, the Type 97, an improved Vickers, and the Type 1, based on the MG15.

The Russian ShKAS was probably the best of the lot, with a high muzzle velocity and a high rate of fire, although the bullet was light. The upgraded Ultra ShKAS had an extremely high rate of fire for its time, but it seems to have seen only limited use. Russian fighters were quick to adopt heavy machineguns and cannon.

Most of these guns were whitdrawn from service rapidly, because they were ineffective against the new generation of combat aircraft. Those carried armour plate and self-sealing fuel tanks. The Browning gun survived in the gun turrets of British bombers, but was increasingly ineffective: At the end of the war only incendiary ammunition was used, because the AP round was not able to penetrate the armour of modern fighters.

Heavy Machineguns

The Browning M2 was the standard armament of US fighter aircraft during WWII. Its development began during WWI, primarily as a weapon for fighters, but it did not reach maturity until the M2 model was introduced in 1932. By the standards of WWII it was rather heavy and its rate of fire was unremarkable, but muzzle velocity was high and the ballistic characteristics very good. The gun was also easy to manufacture and extremely reliable. In 1948 the M3 was introduced, with the rate of fire increased to 1200 rpm. Both the M2 and M3 are still in use today.

The Japanese Army Ho-103 was a copy of the Browning .50. The copy was lighter and had a faster rate of fire, but it also fired a smaller round, with a cartridge case 81mm long instead of the 99mm of the Browning. The Japanese Navy also copied the Browning, to create the Type 3, but in typical style it chose to use different ammunition. The 13.2mm calibre was the same as used by Hotchkiss anti-aircraft guns, although the 99mm cartridge case was almost identical to that of the Browning. The Navy also used the Type 2, which was a copy of the MG131, retaining the dimensions of its 13 x 64B ammunition, but with percussion firing instead of electrical ignition.

The German MG 131 with its light 13mm ammunition was developed for synchronized installations, typically in the engine cowling of German fighters. It was a light weapon, and it had electrical firing to simplify the synchronisation. It was used in German fighters until the end of the war, because --- despite rumours suggesting otherwise --- it was not possible to install the MG151 in the engine cowling of small fighters such as the Bf 109 or Fw 190. The MG151 was a much heavier, much more powerful weapon, and it replaced the 20mm MG FF as centreline armament on the Bf 109F. The gun was later enlarged to 20mm calibre as the MG 151/20, and this replaced the original 15mm version in fighter applications. In 1943 a few thousand guns based on the MG151 were manufactured in the USA, redesigned to fire a very powerful 0.6 inch (15.2 x 114, 76.5g) round. This redesign had created new problems, and this gun was was never used in combat.

The Italian Breda-SAFAT was the main weapon of Italian fighters in the early years of the war, and most (CR.42, G.50, Re.2000, and M.C.200) carried only two. Unfortunately for them, it was not a very good gun. It fired a Vickers 12.7 x 81SR cartridge, the same as adopted by the Japanese Army for the Ho-103. But the Japanese gun was lighter and fired faster.

Again, the Soviet Berezin UB was probably the best gun, with a ballistic performance similar to that of the Browning gun, but a considerably higher rate of fire. The UBK was the version for normal, fixed installations. In synchronized UBS installations the rate of fire was reduced to 800 rpm. This was significant, for most Soviet fighters had their guns on the engine cowling or in the wing roots.

The 20mm cannon

The Swiss Oerlikon guns provided the inspiration for many 20mm guns, so they are included here for reference. The Oerlikon F was the basis for the German MG FF and the Japanese Type 99 model 1. The Type 99 model 2 was more similar to the L. And the Japanese Hispano-Suiza S.9 and S.7 were also versions of an Oerlikon gun, probably the S.

The Luftwaffe at first experimented with the MG c/30L, a weapon derived from a Flak gun. It was very powerful, but heavy and slow-firing. A lighter version, the Lb 204 which fired different ammunition (20 x 105B or 20 x 105, 134g) at 400 rpm, later appeared as defensive armament on Do 18E and Bv 138 flying boats. But the weight and slow rate of fire argued against the use of the MG C/30L on fighters, and instead the Germans adopted the Ikaria MG FF, a weapon with a low muzzle velocity, but lighter and with a modestly higher rate of fire. It was a derivative of the Oerlikon F cannon. The MG FF was usually fed from a 60-round drum. The MG FF/M version fired a smaller round with a higher muzzle velocity, but it was still a short-range weapon, and its ballistic characteristics were very different from those of the 7.92mm machineguns installed on the same fighters (mainly Bf 109E).

From the end of 1940 onwards the MG FF was replaced by the excellent Mauser MG 151/20 cannon, derived from the 15mm MG151. Because the overall length of the cartridge remained the same, the 20mm version fired a heavier projectile with less propellant, and had a lower muzzle velocity than the 15mm. Some weight was saved by reducing the length of the barrel. Again, both 115g and 92g projectiles could be fired. The MG151/20 was an excellent weapon against fighters, but the Bf 109F carried only a single cannon. Later fighter began carrying more guns, but against sturdy bombers such as the B-17 even the MG 151/20 was insufficient. The MG151/20 was also used by the Italians, and some were shipped to Japan by submarine. Recently, a development of the MG151 was made in South Africa.

The USSR had an excellent cannon in the ShVAK, a compact, fast-firing and powerful weapon. The ShVAK was basically an enlarged ShKAS. It was fitted to Soviet fighters throughout the war, but in 1945 its replacement by the equally performant but much lighter B-20 began.

For French fighters such as the Dewoitine D.501 and Morane-Saulnier Hispano-Suiza had manufactured a licence-built versions of the Oerlikon cannon, as the S.7 and S.9. These weapons were regarded as unsatisfactory, especially for installation between the cylinder banks of Hispano-Suiza V-12 engines. Engine designer Mark Birkigt decided to develop a new 20mm cannon, the HS.404. It had a different action and a much higher muzzle velocity. By 1939 it was in production also in Britain, but not until the autumn of 1941 was a reliable belt-feed mechanism for it produced. This cannon was mostly used by British and by some American fighters.

The Hispano was a rather big gun (2.36m long, compared to 1.76m for the ShVAK), and its rate of fire was lower than that of other 20mm cannon. However, it fired a heavy projectile with a high muzzle velocity. The Mk.V was a lighter version, without in-flight cocking mechanism and with a shorter barrel. It could be installed within the wing of fighters such as the Hawker Tempest. This model is still in use.

Again, the Japanese Army and Navy used different weapons. The Army used the 20mm Ho-5, that was derived from the Browning .50, and was probably the best Japanese fighter gun of the war. It replaced the older Type 97, which had been derived from an anti-tank gun. The Ho-5 was lighter than the older gun, but the cartridge case was reduced from 125mm to 94mm, and muzzle velocity suffered accordingly. While the Ho-5 was under development, some Army fighters were equipped with the German MG151/20. In August 1943 a submarine had brought 800 MG151/20 cannon from Germany, and they were installed in Ki.61s.

The Navy used mainly the Type 99. The model 1, another derivative of the Oerlikon F gun, fired a heavy projectile, but its low muzzle velocity gave it poor penetration and poor ballistic characteristics, and its rate of fire was equally unimpressive. For the model 2 the Japanese used the Oerlikon L as starting point. By using a bigger cartridge case, 101mm long instead of 72mm, and a longer barrel, the muzzle velocity was raised to an acceptable value. Later the mechanism was refined, and the rate of fire significantly increased.

Heavier Cannon

The Browning M4 was installed in US fighters such as the P-39 Airacobra. This was a heavy, slow-firing cannon, with a small number of rounds in an ammunition drum. Such heavy, slow-firing guns were intended to destroy bombers, but their ballistic characteristics were not up to the task. And the fighters that used it, such as the P-39 and early models of the P-38, carried only one. American designers later sought to compensate for the low rate of fire of the M4 by installing four or six of them in experimental fighters, but these plans never matured. Because of their low rate of fire these guns were more useful against ground targets, although it did not have sufficient muzzle velocity to penetrate armour.

A later development, the M10, had the feed mechanism modified for a disintegrating belt, a change that allowed ammunition to be increased from 30 to 58 rounds. It was sliightly heavier, 109kg, but its performance was identical. This weapon was installed in later models of the P-63 Kingcobra.

The M9 was a very different weapon. The large cartridge case gave the same HE round as the M4 a considerably higher muzzle velocity. One of the types of ammunition available was a 752g armour-piercing projectile with a muzzle velocity of 930m/s, and at a distance of 460m this penetrated 6cm of armour plate. At the same distance the M4 could penetrate only 2cm of armour. It is obvious that the M9 was much better suited for ground attack; but it seems that the only aircraft in which it was ever fitted was the one-off P-63D.

The Germans initially developed the MK101 for air-to-air use, the intention being to attack bombers from a safe distance. But its weight and low rate of fire seem to have excluded this use; instead it was used by ground attack aircraft. It was useful against (lightly) armoured ground targets. The MK103 was lighter than the MK101, had electric firing instead of percussion firing, and fired faster. It was an excellent, powerful weapon, but again it could not be carried by a fighter without considerable loss of performance. Only at the very end of the war did some fighters, such as subtypes of the Bf 109K, carry a MK103 gun on the centreline.

Because the fight against heavy allied bombers required a 30mm cannon, the lighter MK 108 was developed, with a much lower ballistic performance, but less than half the weight and bulk. Fighters could carry two or even four MK 108s. This gun had a heavy punch, but because it was a short-range weapon fighter pilots had to get really close to their targets. Its use required strong nerves and better training than German pilots received during these last years of the war.

An alternative was the BK 5, originally an anti-tank gun. The advantage of this weapon was that it could be fired at bomber formations from beyond the range of their defensive armament: A return to the concept behind the MK101 and MG c/30L. Its disadvantages are obvious. It was installed in some Me 410 fighters, and experimentally fitted in a Me 262.

Big Russian cannon such as the NS-37 were mostly intended for use against ground targets, although they were occasionally fired in air-air combat. Usually only a single cannon of this type was carried, typically between the cylinder banks of the Klimov engines of the Yakovlev fighters. These small fighters successfully carried even the large NS-45, but the recoil of the NS-57 was too much for them.

The first gun in service, in 1940, was the powerful VYa, with a 152mm long cartridge case. It was installed mainly in Il-2 ground attack aircraft, but also in some fighters. In 1942 the NS-37 appeared; this gun could penetrate 40mm of armour at an angle of up to 40 degrees. And from 1945 onwards, the NS-23 was introduced, a version of the NS-37 scaled down to 23mm. It replaced the much heavier VYa in fighters, but because the cartridge was only 115mm long the muzzle velocity was reduced. The NS-23 was a more typical fighter weapon, less suitable for ground support missions. It would stay around for a long time.

The Japanese Army installed big cannon in ground attack aircraft, such as the developments of the Ki.45 Toryu, but these were unimpressive weapons. The Type 98 was a hand-loaded 37mm cannon, derived from a French army weapon. The achievable rate of fire was about 15 rpm. The semi-automatic Ho-203, with a 25-round drum, was a much-needed improvement. The Ho-203 was regularly found on fighters, such as subtypes of the Ki.44, despite its low rate of fire and its low muzzle velocity. The big Ho-401 was also intended for anti-armour and anti-shipping attacks, but occasionally it was used against B-29 bombers as well. Not because it was effective, but because the Japanese did not have any better defense against the B-29. A desperate measure was the installation of the 75mm Type 88 anti-aircraft gun in a bomber, to create the Ki.109 "fighter". It seems obvious that this was a bad idea, especially as the gun itself was rather mediocre, but without the planned turbosuperchargers the Ki.109 could not even get close to the B-29s.

The Ho-301 was one of the most unusual cannon used during the war. It fired caseless rounds, which had the propellant charge in the back of the projectile. It had an effective range of only 150m and was effective only against ground targets.

The Fighters

Fiat C.R.42 Falco

• Two 12.7mm Breda-SAFAT guns, with 400 rounds per gun. Ammunition for 34 seconds.
• They fired 23 rounds per second, corresponding to 0.86 kg.
• This pathetic armament was very much the standard for the Italian fighters of 1940. Some fighters had 7.7mm guns added, but because they were underpowered they could not carry much more. The Italians finally had to adopt German engines and German guns for their fighters.

Nakajima Ki.43 Hayabusa

• Two 12.7mm Ho-103 guns with 250 rounds per gun, enough ammunition for 17 seconds.
• 30 rounds per second, or 1.14 kg/sec.
• The production of the Ki.43 actually began with Type 89 7.7mm guns. This was clearly insufficient, and when production of the Ho-103 allowed, it first replaced one and then both of the smaller weapons. The Ki.43 was still under-gunned, and remained so until the end of the war.

Supermarine Spitfire Mk.IA

• Eight Browning .303 guns installed in the wings. 300 rounds per gun, enough for 16 seconds of fire.
• 152 rounds per second, or 1.71kg/sec output
• The RAF was quick to understand that heavy firepower was needed, but its initial choice was an unfortunate one. The .303 was chosen over the .50 because of its higher rate of fire and better reliability, but the .303 round lacked the power to penetrate armour, and was far too light to do structural damage. Pilots preferred to use incendiary rounds, also because they could see them hit the target. Although some pilots had their guns "synchronized" to converge at a point, it was more common to have some spreading, to simplify aiming.

Yakovlev Yak-3

• One ShVAK cannon mounted between the engine banks, with 120 rounds. One Berezin UB in the forward fuselage decking, with 250 rounds. That was enough for 9 and 19 seconds, respectively.
• Both guns fired 13 rounds per second, but the ShVAK cannon put out 1.2kg and the machinegun 0.6kg.
• The Yakovlev fighters had high performance, but their small size and limited engine power limited their armament. The Lavochkin fighters, although also small, had more engine power and could carry heavier armament. To some extent these disadvantages were compensated by the excellence of the Soviet guns, but their effectiveness was reduced by the primitive gunsights.

Messerschmitt Bf 109E-3

• Two MG FF cannon in the wings, with 69 rounds each; two MG 17 machineguns in the engine cowling, with 1000 rounds per gun. The cannon ammunition was enough for 8 seconds, the machineguns had ammunition for 55 seconds.
• Output per second was eightteen 20mm shells and 37 7.92mm bullets. The cannon were responsible for firing a weight of 2 kg/sec. The contribution of the MG 17s was 0.37 kg/sec.
• The two MG 17 machineguns were too light to be very effective. The MG FF cannon were powerful, but their effective range was short. Ballistic characteristics of the MG FF and MG 17 were too different. The Bf 109E probably was a better bomber interceptor than the British fighters, but its role in the battle of Britain was that of an escort fighter.

Mitsubishi A6M2 model 21 Reisen 'Zeke'

• Two 7.7mm Type 97 machineguns in the front fuselage, with 500 rounds per gun. Two 20mm Type 99 model 1 cannon in the wing, with 60 rounds per gun. The cannon had ammunition for 7 seconds, the machineguns for 30 seconds.
• The cannon fired 16 shells per second, or 2.32kg. The machineguns fired 33 rounds in the same time, or 0.37kg.
• To install cannon in a fighter was an advanced concept, and here the Japanese Navy had a lead on some other services, notably the Japanese Army. But the Type 99 model 1 was too slow-firing, had a too low muzzle velocity, and its ballistic characteristics did not match that of the machineguns. There is a remarkable similarity with the Bf 109E.

North American P-51D Mustang

• Six Browning .50 machine guns. The two inboard guns had 400 rounds each, enough for 32 seconds. The four outboard guns had 270 rounds, enough for 22 seconds.
• Output per second was 75 rounds, or a weight of 3.6kg per second.
• Most pilots liked the .50 gun, but it lacked the power to do structural damage to enemy aircraft. Postwar research demonstrated that only armour-piercing incendiary rounds were really effective, by setting fire to ammunition or fuel. This armament was sufficient for the Mustang, because it was an escort fighter, that had to fight mostly against enemy fighters. The guns were usually set to converge at 300 yards, and 2 degrees above the normal flight attitude. The ammunition supply was relatively large, and that was also beneficial for an escort fighter.

Supermarine Spitfire Mk.XIVE

• Two Hispano cannon in the wing, with 120 rounds each. Two Browning .50 guns, with 250 rounds each. The cannon ammunition lasted for 12 seconds; the machinegun ammunition for 20 seconds.
• The two cannon fired 20 rounds per second, the two machineguns 25. Total output was 4kg per second.
• The E-wing was the definitive wartime armament for the Spitfire, although after the war four 20mm cannon were fitted. It was a small fighter, and its thin wing complicated armament installations. But the E-wing armament was very effective. An important factor was the use of gyroscopic gunsights by the Allied, because they greatly improved accuracy. The Germans developed similar gunsights, but they were never reliable enough to be useful.

Kawasaki Ki.61-I-KAI-Hei Hien 'Tony'

• Two 20mm Ho-5 guns with 120 rounds per gun, and two 12.7mm Ho-103 guns with 200 rounds. The machineguns had ammunition for 13 seconds and the cannon for 8 seconds.
• The cannon put out 28 rounds per second. Assuming a shell weight of 120g, that corresponds to about 3.4kg/sec. The machineguns contributed 30 rounds, or 1.14kg. Total about 4.5kg/sec.
• The Ki.61 was the first fighter of the Imperial Japanese Army that was the equal or better of the Western designs it encountered. Its armament became the standard for later IJA fighters; the Ki.84 carried the same guns, but more ammunition.

Mitsubishi A6M5b model 52B Reisen 'Zeke'

• In the front fuselage one 7.7mm Type 97 with 500 rounds, and one 13.2mm Type 3. Wing cannon two 20mm Type 99 model 2 with 125 rounds per gun. The cannon had ammunition for 10 seconds, the light machinegun for 30 seconds.
• The cannon fired 25 shells per second, or 3.55kg. The 13.2mm machinegun fired 13 rounds in the same time, a weight of 0.96kg. The light machinegun contributed 17 rounds, or 0.19kg. The total is 4.7kg.
• Upgrading the armament of the A6M gave later models a far greater killing power. Much of this was because of the Type 99 model 2 cannon, which in its final version fired a bigger shell than the Hispano at a higher rate of fire, and weighed less. This was a vast improvement, but it came too late to save the IJN. The last IJN fighters of the war, such as the N1K2-J Shiden-KAI, had four Type 99 model 2 cannon.

Focke-Wulf Ta 152H-1

• One MK 108 cannon firing through the propeller spinner, and two MG 151/20 cannon in the wing roots. The 30mm cannon had 90 rounds, the 20mm cannon had 175 rounds each. This was ammunition for respectively 9 and 14 seconds of fire.
• Per second, ten 30mm shells and 24 20mm shells were fired. This amounted to a weight of 5.9kg.
• This high-altitude interceptor was armed to fire a short, heavy burst at its target. The MK 108 cannon was a low-velocity weapon, designed to inflict heavy structural damage to the heavy bombers of the 8th AF.

Messerschmitt Me 262A-1a

• Four MK 108 cannon in the nose. Two had 80 rounds, two had 100 rounds, for respectively eight and ten seconds of fire.
• Forty 30mm shells per second, or 12.5kg per second.
• The armament of the Me 262 was deadly against heavy bombers. Because of the low muzzle velocity of the MK 108, it was not very suitable for fighter-vs-fighter combat, but in principle the Me 262 could outrun any enemy. In practice the Me 262 were always heavily outnumbered by the escort fighters.

Evolution

Some WWII fighters were armed with was essentially World War I armament: Two machineguns, typically installed in the upper decking of the front fuselage, and with the breeches within reach of the pilot so that he could clear stoppages. Such armament was carried by Italian and Japanese Army fighters; as a concession to modernity heavy machineguns were substituted for the rifle-calibre weapons.

In the first phase the rifle-calibre machinegun was still important. Fighters either carried a homogenous armament of such guns, or they used a mixture of rifle-calibre guns with cannon or heavy machineguns. Examples of the first approach are the eight Browning .303s in the Spitfire and the four MG17s in the early Fw 190. Examples of the second approach are the MG FF and MG 17 weapons of the Bf 109E, the two .50 and four .303 Brownings of the early P-51, or the two 20mm cannon and two 7.7mm guns in the A6M2. The first phase ended when it was generally understood that the light machinegun was ineffective against modern combat aircraft.

In the second phase there were still two options. Either a homogenous armament of heavy machineguns was used, or a mixture of more modern 20mm cannon with machineguns. The first approach was chosen almost exclusively by the USAAF, which equipped its fighters with six or eight .50 Browning guns. The second approach was far more common, and used by fighters such the Spitfire, the Bf 109, or Ki.84. The cannon were now in general belt-fed, high-velocity weapons with a satisfactory rate of fire. The disadvantage of cannon was that their weight and recoil precluded the use of more than one or two. Hence they had to be mixed with machineguns, with different ballistic characteristics, different ammunition and different maintenance requirements. The disadvantage of an armament of heavy machineguns only was that it lacked the destructive power to be effective against anything but small fighters or lightly constructed bombers.

The third phase, which lasted well beyond WWII, was characterized by a switch to a homogeneous armament of 20mm cannon. Examples of such armament are the last Spitfire models, the Typhoon and Tempest, the Soviet La-7, and the Japanese N1K-2J. Usually four 20mm cannon were carried. This was also the standard armament for most post-war fighters, except those of the USAAF. Again, there was a second option: That of heavy "bomber killer" armament. Here the German MK 108 cannon must be mentioned, as installed in the Me 262. Such cannon were either low- velocity, low-rpm weapons, or they were extremely heavy; in either case they reduced the suitability of the fighter for combat against other fighters. Because of this and the introduction of spin-stabilized and folding-fin rockets, such armament was installed in few post-war fighters, but one that must be mentioned is the MiG-15.

The use of WWII fighter armament ended with the introduction of revolver cannon (developed in Germany during the war), Gatling-type rotary cannon, or Gast-derived dual-barrel cannon. These weapons with their much higher rate of fire revolutionized fighter armament. The introduction of guided missiles came later.

Acknowledgements

Military Aircraft Database . Index