Flying Guns: Gun Tables

For every gun in the tables, the following parameters are given:

The Name of the gun. This should be an obvious fact, but alas there are a lot of mistakes around this. Especially Japanese guns are poorly documented, and as there were a great number of different guns in service in the Japanese Army and Navy, the potential for confusion is enormous.

The type of round as, for example, 13 x 64B. The first number is the caliber, in millimeter. This represents some approximation of the diameter of the barrel and the projectile. It is not a very accurate parameter, because there are several different conventions to measure this, and to make things even worse, armed forces sometimes choose arbitrary numbers for administrative convenience. The second number is the length of the cartridge case, again in millimeter. The length of the case is used instead of the length of the projectile or of the overall length of the cartridge, because the first is characteristic for the gun, while the other two are dependent on the type of projectile used. To this case length one appends an indication for the shape of the base of the cartridge case, if required: R for Rimmed and SR for Semi-Rimmed cases, RB for reBated Rimless cartridges (some authors list these as RR), and B for Belted cartridge cases. Such variations in shape are usually linked to the operating principle of the gun. 

The weight of the projectile in gram. Note that guns are usually able to fire several types of ammunition, and different types of ammunition were usually mixed. Hence an average is given, or in some cases a typical value. Because projectiles with different weights have different muzzle velocities, this implies that the value for the muzzle velocity is also an average. 

The rate of fire in rounds per minute. Note that for synchronized guns, which fire through the propeller disc, the average rate of fire can be significantly lower.

The muzzle velocity in meter per second. For those more familiar with feet: A foot is 0.3048 meter (exactly, by definition, since 1959). A higher muzzle velocity gives a flatter trajectory, a shorter time of flight towards the target, and better armour penetration. The muzzle velocity is a characteristic of the gun, but also depends on the weight of the projectile and the type of propellant in the cartridge case, so again may vary depending on the ammunition type. 

The weight of the gun, in kilogram. (A pound is 0.45359237 kilogram by exact definition.) The importance of weight for aircraft designers is obvious. For reference, it is good to keep in mind that the empty weight (without fuel, ammunition and pilot) of a single-engined, single-seat World War II fighter varied between 2,000 kg and 5,000 kg. Another consideration is that the guns were often in the wings, far from the center of gravity, and to achieve good manoeuvrability it is best to concentrate the mass around this center. The need for ammunition storage, structural reinforcement, and access panels of course added significantly to the installed weight. Larry Bell estimated the weight penalty for four .50 Browning M2 wing guns as about 1,000 lb [Cobra! by Birch Matthews, Schiffer, 1996].

The quality factor Q is a standard that Russian designers have been using to evaluate and compare guns. Basically, it is a power-to-weight ratio: The kinetic energy at the muzzle (which is one half the projectile weight multiplied with the square of the muzzle velocity) multiplied by the rate of fire in rounds per second, and divided by the weight of the gun. Essentially, this says how much power a gun produces for a given weight, and is similar to the horsepower-per-weight figure for engines. This Q value is a measure of the efficiency of a gun, not of its firepower: A light gun with a modest ballistic performance will have a better Q value than a powerful, but too heavy gun. Evidently it contains no information about reliability, accuracy, range, ammunition performance, or manufacturing cost. Nevertheless it is a sensible way to compare guns.

The factor M is another quality factor: The mass output, divided by the weight of the gun. The mass output is the weight of the projectiles, multiplied by the rate of fire in rounds per second. This too is a measure of the efficiency of the gun, not of its power.

Rifle-Calibre Machine Guns

Rifle-calibre machine guns (RCMGs) ranged from 7.5 mm to 8 mm. Originally, these were often infantry weapons, which fired the same ammunition as an infantry rifle for logistical reasons. They were adapted for air use, and such weapons became standard armament for fighters during the First World War. Even then it was observed that they were somewhat deficient in destructive power, and too easily countered by installing armour. Yet they were still in use in the early years of WWII. Compared to the guns of WWI these RCMGs were substantially improved: They were more reliable and had a higher rate of fire. Nevertheless most of the rifle-caliber guns were withdrawn from service by the second half of the war, because they were ineffective against the new generation of combat aircraft, that carried armour plate and self-sealing fuel tanks. The Browning .303 gun survived in the gun turrets of British bombers, but only because an alternative was not readily available.

Name CartridgeProj.
Rate of
Browning .30 M2 7.62 x 6310.5120087010.47.620.2
Browning .303 7.7 x 56R10.61150750105.720.3
Darne 7.5 x 549.21100-12008307.87.822.6
MAC 1934 7.5 x 54 9.21200-15008308.58.424.4
MG 17 7.92 x 57 10.8120077512.65.117.1
MG 81 7.92 x 57 10.816007456.312.745.7
Breda-SAFAT 7.7 x 56R 10.6800-90073012.53.212.0
Type 89 Flexible7.7 x 58SR10.51500810283.19.4
Te-47.7 x 58SR10.57508109.14.714.4
Type 89 Fixed7.7 x 58SR10.590081012.74.112.4
Type 98 Flexible7.92 x 5710.810007757.27.525.0
Te-17.7 x 58SR10.590081011.84.413.3
Type 100 / Type 17.92 x 5710.8220077516.77.123.7
Type 92 Flexible7.7 x 56R10.66007508.53.512.5
Type 97 Fixed7.7 x 56R10.690075011.83.813.5
Type 1 Flexible7.92 x 5710.810007756.87.926.5
ShKAS 7.62 x 54R10.9180087010.611.730.8
Four Browning .303 guns in the wing of a Hurricane. The leading edge of the wing is to the right.

The best known gun in this list is the Browning. The origins of this recoil-operated weapon go back to a gun designed in 1917 for use by the infantry. (The earlier Model 1895 Browning was gas-operated.) The M2 version was developed in the early 1920s for installation in aircraft, and had a higher rate of fire than the older models. The British version fired rimmed .303 ammunition instead of rimless .30 ammunition, and was also modified to fire from an open bolt instead of a closed bolt, because the British used cordite propellant that was sensitive to heat. Eight .303 Browning guns were installed in the first monoplane fighters of the RAF, the Spitfire and the Hurricane, although concerns about the effectiveness of rifle-calibre machineguns had already been voiced during WWI. A major advantage of the Browning over the older Vickers guns was its reliability. The pilot could not reach guns installed in the wings to clear stoppages, so reliability was essential.

FN also produced versions of the Browning in several different calibres, and speed the gun up to a nominal 1500 rpm (1400 rpm for a new gun, 1700 rpm for a gun that had been run-in). This FN-Browning was also used by the French air force in their 7.5×54 calibre, mostly for imported aircraft. 

The gas-operated French 7.5 mm Darne was used in both fixed and movable installations. It was not a very reliable gun, and before war broke out the air force had retired the weapon. It was still in service in naval aircraft. The air force instead switched to the MAC 1934, which was also a 7.5 mm weapon. The initial version was drum-fed, using large 300-round drums, but in 1939 a belt-fed model was introduced.

Twin MG 17 guns were installed under the engine cowling of Messerschmitt Bf 109s, until they were replaced by the MG 131 in the Bf 109G-5. This is a Bf 109E-4. Note the staggered position of the guns, to allow an easier fit of the ammunition magazines.

The German MG 17 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 1000 rpm. The standard flexible gun, the MG 15, was very similar. In 1939 the Luftwaffe introduced the superior Mauser MG 81, a development of the MG 34 of the Army. The MG 81 was much lighter than the MG 17 and had a high rate of fire. But because the Luftwaffe recognized that the 7.92 mm calibre was obsolete as fighter armament, the MG 81 was used almost exclusively in defensive installations on two-seat fighters and bombers. There the MG 81 was usually found in the twin-gun MG 81Z installation. It was the best performer of the RCMGs, slightly superior even to the Soviet ShKAS. 

The Italian Breda-SAFAT 7.7 mm gun was fairly important in the early years of World War II, and earlier in the Spanish civil war. It was used in combination with the 12.7 mm version, in an attempt to boost the feeble firepower of the underpowered Italian fighters without inflicting a too large weight penalty on them. 

No country had so many different guns in use as Japan, with so many different types of ammunition. The Japanese Army and Navy independently produced nearly identical weapons, and with non-interchangeable ammunition; this is symbolic for the lack of cooperation between the two services. Considering how weak their logistical situation was to begin with, it was also thoroughly irresponsible.

The Army used copies of the Vickers as the Type 89 fixed and the Te-1, which was a flexible version of this gun. The 7.7 mm Type 89 flexible was an indigenous magazine-fed design used in flexible, defensive installations, twin guns being placed on a single mount. If these guns were used individually, they were known as the Te-4 or Type 89 (modified single). The Type 100 or Type 1 were Japanese versions of a Czech design, also used in twins, and firing 7.92 x 57 ammunition. Finally, the German MG 15 was used the Type 98 flexible

The Japanese 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, also based on the MG 15.

The Russian ShKAS had a high rate of fire and a high muzzle velocity, and was the best of the RCMGs found in fixed installations. The powerful ammunition carried special marks, to prevent its accidental use in rifles. There was also an upgraded model, the Ultra ShKAS, which had an extremely high rate of fire for its time: 2700 rpm. Some of these guns were installed on I-16s and used in combat during the Winter War with Finland, but it was insufficiently reliable to be put into series production. Russian fighters were also quick to adopt medium-calibre machineguns and cannon, making further development of the rifle-calibre weapons superfluous.

Medium Calibre Machine Guns

Traditionally one distinguishes rifle-calibre and medium-calibre machineguns. The latter are often called heavy machineguns (HMGs), but this can lead to confusion because that term is also applied to some rifle-calibre machineguns. Medium-calibre weapons are .50 and similar, in practice ranging from 11 mm to 15 mm. The bullet is up to four times heavier than that of a rifle-calibre machinegun, and can be fired at a high muzzle velocity. Hence it usually has good ballistic characteristics. The rate of fire is usually much lower than that of rifle-calibre weapons.

As the war progressed, aircraft were modified with more effective armour and better self-sealing tanks. The US Navy, for example, considered its aircraft well protected against .50 fire, and even 20 mm rounds.[The Story of the Self-Sealing Tank, in US Naval Institute Proceedings, February 1946. Page 205.] German and British fighters were designed to be protected against .50 fire from the front, and 20 mm fire from the rear. However, the .50 remained a reasonably effective weapon against fighters and the lighter bombers, if enough guns were installed; usually six in American-built fighters. Only during the war in Korea the .50 was clearly proved to be deficient in destructive power against the new jet fighters.

Name Cartridge Proj.
Rate of
Browning .50 M212.7 x 9943.3750-850880297.719.9
Ho-103 (Type 1)12.7 x 81SR34.2800-900765236.221.1
13 mm Type 2 13 x 64B36.2900730178.531.9
13 mm Type 3 13.2 x 9949.5800795316.721.3
MG 131 13 x 64B36.2900730178.531.9
MG 151 15 x 9664.5700905427.317.9
Breda-SAFAT 12.7 x 81SR34.2700765294.013.8
Scotti12.7 x 81SR34.2700765235.117.3
UBK 12.7 x 10852.010508602513.536.4
UBS12.7 x 10852.08008602510.327.7
Most US fighters of the war carried Browning .50 M2 guns. Usually six were installed. These are the inboard guns in the left wing of a Grumman F4F-4 Wildcat. Two more guns were further outboard.

The Browning .50 M2 was the standard armament of US fighter aircraft during WWII. Its development began at the end of WWI, primarily as a weapon for fighters, because it was understood that rifle-calibre machineguns did not have enough destructive power and range. (Similar attempts were made in Britain, but the British .50 guns did not enter widespread service.) The Browning .50 was first adopted in the early 1920s as the M1921, but 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, although the barrels wore out quickly especially if long bursts were fired. In slightly different versions it was used by all US military services, and it was easy to exchange spare parts or switch factory output from one service to another.[50-caliber Machine Gun in US Naval Institute Proceedings, March 1944. Page 364.] The Browning .50 still was the standard armament of USAF fighters during the Korean war, but then in the upgraded M3 model, introduced in the last months of WWII. The rate of fire of the M3 was increased to 1200 rpm.

The Japanese Army Ho-103 was a copy of the Browning .50. The copy was lighter and had a higher rate of fire, but it also fired a smaller round, with a cartridge case 81 mm long instead of the 99 mm 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 13.2 mm calibre was the same as used by Hotchkiss anti-aircraft guns, although the 99 mm cartridge case was almost identical to that of the Browning. The Navy also used the Type 2, which was a copy of the German MG 131, retaining the dimensions of its 13 x 64B ammunition, but with percussion firing instead of electrical ignition.

The German MG 131 with its light 13 mm ammunition was developed for synchronized installations, typically in the engine cowling of German fighters. It had electrical firing to simplify the synchronisation. The MG 131 was a light weapon, but this was achieved by combining a modest muzzle velocity and a light projectile. Despite its limitations, it was used in German fighters until the end of the war, because it was not possible to install the MG 151 in the engine cowling of small fighters such as the Bf 109 or Fw 190; only the Do 335 and Ta 152C had the MG 151 as cowl gun. The MG 151 was a much heavier, much more powerful weapon, and it replaced the 20 mm MG-FF as centreline armament on the Bf 109F. During the war a copy of the MG 151 was designed in the USA, modified to fire a very powerful .60 (15.2 x 114, 76.5 g) round. But this T17 gun never reached service, and only about 350 were made.

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 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. The Breda-SAFAT was reliable and accurate, however, and its ammunition was considered very effective. A Scotti gun in the same calibre was also produced. It was considered superior, and was mostly used in flexible installations. 

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 installations in aircraft wings. The synchronized UBS for cowling gun installations had a lower rate of fire, though a still creditable 800 rpm. This was significant, for most Soviet fighters had their guns on the engine cowling.

The 20 mm cannon

The advantage of cannon firing high-explosive rounds, as illustrated in a pre-war French source. Only the black parts of the bomber are vulnerable to machineguns: Crew, engines, fuel tanks. Cannon hits anywhere may cause sufficient damage to down the aircraft. From l’Aviation Militaire Francaise, by Pierre Barjot, published shortly before WWII.

Cannon are now usually defined as weapons with a calibre of 20 mm or larger, but historically operators have used several other definitions. 

It is usually considered that 20 mm is the smallest practical calibre in which explosive projectiles can be used. Smaller ones have been made, and the Japanese even made HEI ammunition for rifle-calibre machineguns. But usually light and heavy machineguns were loaded with a mixture of incendiary and armour-piercing rounds. Such ammunition also existed for 20 mm cannon, so the projectile was not necessarily high-explosive. Fusing was always critical for high-explosive rounds. A too sensitive or too fast fuse would make the projectile ineffective, as it would explode when hitting the outer plating of the aircraft. A too slow fuse could also have disadvantages, as the projectile could pass through the aircraft before exploding. It took some time to develop suitable fuses. Early British 20 mm rounds were ineffective because they exploded too fast, and for some time solid AP rounds were the most used ammunition for the Hispano cannon.

Name Cartridge Proj.
Rate of
    (gram) (rpm)(m/s) (kg)  (kW/kg) (1/s)
Oerlikon FF F 20 x 72RB 128520600248.346.2
Oerlikon FF L 20 x 101RB 1285007503010.035.6
Oerlikon FF S 20 x 110RB 122470830398.424.5
MG c/30L 20 x 138B 134300-350950645.111.3
MG-FF 20 x 80RB 134530600287.642.3
MG-FF/M 20 x 80RB 104530640286.732.8
MG 151/20 20 x 82 105700-750725427.930.2
ShVAK 20 x 99R 95800750 – 770428.730.2
B-20 20 x 99R 95800750 – 7702514.650.7
HS.9 20 x 110RB 122360-420830485.716.5
HS.404 20 x 110 130700880609.825.3
Hispano Mk.II 20 x 110 1306008805010.126.0
Hispano Mk.V 20 x 110 1307508404213.738.7
Type 94 Flexible20 x 99RB 127380675434.318.7
Ho-1 20 x 125 144400805456.921.3
Ho-3 20 x 125 144400805456.934.6
Ho-5 (Type 2) 20 x 94 96750-850715378.843.0
Type 99-1 20 x 72RB 129520525265.943.0
Type 99-2 20 x 101RB 128490750348.630.7

The Swiss Oerlikon guns provided the inspiration for many 20mm guns. The original Oerlikon aircraft cannon was designated FF for flügelfest, wing-mounted. Later the gun was adopted for three types of ammunition, and the original version became the FF F, while the other two were called FF S and FF L. The FF F was copied as the Japanese Type 99-1, while the Type 99-2 was a license-built copy of the FF L. The French Hispano-Suiza HS.7 and HS.9 were based on the FF S. The German MG FF was based on the FF F, but the weapon was entirely redesigned. 

The Luftwaffe at first experimented with the MG c/30L, a weapon derived from a Flak gun. It was very powerful, and in principle it could be used to engage the enemy from a safe distance. But it was also heavy and slow-firing. (A lighter version, the Lb 204, which fired different ammunition (20 x 105B or 20 x 105, 134 g) at 400 rpm, later appeared as defensive armament on Do 18E and Bv 138 flying boats.)

Instead the Germans adopted the Ikaria MG-FF, a weapon that was much lighter and had a modestly higher rate of fire, but also had a low muzzle velocity. It was a reengineered version of the Oerlikon FF F cannon. The MG-FF was usually fed from a 60-round drum. The MG-FF/M version was modified to fire the new 92 g projectile, often called Minengeschoss. This was a thin-walled HE projectile, with more high explosive than the older, conventional 134 g HE projectile, and therefore greater destructive power against “soft” targets. The main disadvantage of the MG-FF was that it was a short-range weapon, and its ballistic characteristics were very different from those of the 7.92 mm machineguns installed on the same fighters (mainly the Bf 109E).

The MG 151/20 20 mm aircraft cannon, here installed post-war in a French Piasecki H-21 helicopter. The four cylinders around the base of the barrel are recoil absorbers, and belong to the gun mount, not to the gun.

From the end of 1940 onwards the MG-FF was replaced by the excellent Mauser MG 151/20 cannon, derived from the 15 mm MG 151. The changes were limited to a change in projectile and barrel. The overall length of the cartridge remained the same, and because the 20 mm version fired a heavier projectile with less propellant, it had a lower muzzle velocity than the 15 mm gun. Some weight was saved by reducing the length of the barrel. In the table these changes produce a slight increase in Q and a large increase in M. 

The MG151/20 was an excellent weapon against fighters, but the Bf 109F carried only one. Later fighters began carrying more of these guns, but against sturdy bombers such as the B-17 even the MG 151/20 was insufficient. This weapon was also used by the Italians, and some were shipped to Japan by submarine.

The USSR had an excellent cannon in the ShVAK, a compact, fast-firing and powerful weapon. The ShVAK was basically an enlarged ShKAS, and it also existed in a (very rare) 12.7 mm version. The ShVAK was fitted to the I-16 Typ 12 (also known as the I-16P), which was first flown in the summer of 1936 and entered service in 1937. A relatively small number of these aircraft, which were the first cannon-armed fighters in service, were completed. Larger number were produced of the Typ 17, which was powered by the more powerful M-25V engine. The ShVAK remained standard armament on Soviet fighters throughout the war, but in 1945 its replacement by the equally performant, much lighter B-20 began. The B-20 was one of the best aircraft guns of the war.

The Bristol Beaufighter carried four 20 mm Hispano cannon in ventral compartiments. In early models, the gun was fed by 60-round drums. When these were empty, the second crewmember had to replace them by full ones… The installation of belt-fed guns was a much welcomed improvement.

For French fighters such as the Dewoitine D.501 and Morane-Saulnier MS.405, Hispano-Suiza had manufactured a licence-built version of the Oerlikon cannon, as the HS.7 and HS.9. Engine designer Mark Birkigt decided to develop a new 20 mm cannon, the HS.404, with a higher performance. The HS.404 had a different action, a higher rate of fire, and a much higher muzzle velocity. The British were impressed, and by 1939 the Hispano was in production in Britain. Originally it was fed from a 60-round drum, but in the autumn of 1941 a satisfactory belt-feed mechanism was produced. The Hispano was slim, but long (2.36 m long, compared to 1.76 m for the ShVAK) and heavy. Rate of fire of the Mk.II version was lower than that of other 20 mm cannon, but the muzzle velocity was high. Initially, solid AP ammunition was preferred, but later in the war a mixture of HE/I and SAP/I was introduced. The Mk.V was a lighter and faster-firing version, without in-flight cocking mechanism (stoppages had been reduced to 1 in 1500 rounds) and with a shorter barrel.

As the Hispano M1 or M2, this weapon was used on a limited scale by the USAAF and slightly more by the USN. In American service, there were frequent complaints about the unreliability of the guns and feed mechanisms. Some of the changes that had been made in British guns to improve reliability were not included in the US guns, which were made directly from French drawings. It also appears that parts were made with excessive tolerances. The USAAF used the Hispano in the P-61 nightfighter and in the P-38 day fighter. The USN installed it in some attack aircraft, such as the Curtiss SB2C dive-bomber, and a small number of F4U fighters. Only after WWII did the USN adopt the 20 mm cannon, then in the improved M3 version, as its standard weapons for fighters.

Again, the Japanese Army and Navy used different weapons. The Army showed an early interest in the use of 20 mm guns in defensive installations, and the Type 94 was installed as a flexible gun in the Ki-20 bomber. It was a derivative of the Oerlikon L, not of the FF-series of aircraft guns developed by Oerlikon, and was already obsolete. Later developments of the Type 97 anti-tank gun were put in service as the Ho-1 and the Ho-3, the Ho-1 for flexible installations and the Ho-3 for fixed installations. These guns were slow-firing and fairly heavy. Some Army fighters were equipped with the German MG 151/20. In August 1943 a submarine had brought 800 of these cannon from Germany, and they were installed in Ki-61s. Finally, the Army adopted the Ho-5, a derivative of the Browning .50 that probably was the best Japanese fighter gun of the war. The Ho-5 was lighter, had a high rate of fire, and it was belt-fed instead of drum-fed. But near the end of the war the Japanese had a shortage of high-strength alloys, and to compensate for the reduced strength of the guns the Army reduced the pressures. Hence the muzzle velocity of the Ho-5 dropped from 820 m/s to 700 – 730 m/s.

The Navy cannon were the Type 99-1 and Type 99-2, copies of the FF F and FF L respectively. Formally (though not in practice), they were adopted in the same year, the Japanese calendar year 2599, or 1939. Both the Type 99-1 and Type 99-2 were produced in different models, and the later models of both guns were belt-fed. Earlier models usually had 60-round ammunition drums. The Type 99-1 was light, but had a poor rate of fire and a low muzzle velocity. It was carried by early models of the Mitsubishi A6M “Zero”, but experience with it was disappointing. Therefore the more powerful Type 99-2 replaced it in later models of the A6M and in the new fighters the Navy introduced near the end of the war. Because it had a bigger cartridge case and a longer barrel, the muzzle velocity of the Type 99-2 was considerably higher; but the rate of fire was lower. The final Japanese development of this weapon was the Type 99-2 model 5, which was speeded up to 620 rpm. This was a very respectable performance for an Oerlikon-derived gun, but it arrived too late and saw no service.

Heavier Cannon

Big cannon were designed for two different roles: Bomber interception and ground attack. The ground attack guns were given a high muzzle velocity for better armour penetration, in combination with an armour-piercing projectile, often with a core of tungsten or another dense metal. Bomber killer guns could have a lower muzzle velocity, to achieve a weight reduction, and they usually fired projectiles with a large amount of high explosive. Generally these weapons were not intended to be used against fighters: The 20 mm weapons were sufficient to destroy fighters, but bombers were much tougher targets. Sometimes high-velocity guns were used to attack bombers from a large distance, outside the range of the defensive armament of the bombers. Therefore this list includes some weapons that were designed for ground attack.

At this point it may be useful to draw attention to the range of Q and M values. For rifle-calibre machine guns, medium-calibre machine guns, and cannon, the average Q is 6.4, 7.8 and 8.3, respectively. For M these values are 20.2, 23.9, and 30.5. Apparently increasing the calibre results in some efficiency benefits: A single 20 mm cannon will be more efficient than its equivalent firepower in multiple rifle-calibre machine guns. However, this variation is still small compared to the quality differences between different guns in the same calibre, so these factors remain reasonably fair values to compare the performance of guns in different calibres. Among these large-calibre cannon we will now find some quite good performers, with a high Q and a high M. Indeed, in terms of mass output vs. weight the 30 mm MK 108 is the most efficient cannon of all. We also find some abysmally bad performers, however, such as the BK 5. These weapons were never designed for aircraft applications, so their designers attached less importance to weight reduction. For their designed purpose, as tank, anti-air or anti-tank weapons, such cannon might still have been excellent; they were unsuitable for aircraft.

Name Cartridge Proj.
Rate of
37 mm M4 37 x 145R680140580962.816.5
37 mm M1037 x 145R6801605801092.816.6
37 mm M937 x 223SR7441408601813.59.6
MK 101 30 x 184B3302309201803.07.0
MK 103 30 x 184B330360-4208601415.615.2
MK 108 30 x 90RB330600-650505607.357.3
BK 3,737 x 263B6601608102952.06.0
MK 214 A 50 x 419R 15401609204903.58.4
BK 5 50 x 419R1540509205401.02.4
MK 112 55 x 175RB10453005952743.419.1
VYa 23 x 152B2005508806910.326.6
NS-23 23 x 1152005506903711.849.5
NS-37 37 x 1957482508901707.318.3
NS-45 45 x 18210652508501709.426.1
Ho-155-I 30 x 114253400650507.133.7
Ho-155-II30 x 1142535006504410.147.9
37 mm Type 94 37 x 134R644manual580122
Ho-203 37 x 112R475120570891.710.7
Ho-204 (Type 4)37 x 144475300-4007101305.421.3
Ho-301 40 caseless5854502451321.033.2
Ho-401 57 x 121R1500804951501.613.3
Type 8875 x 497R6490manual720480
30 mm Type 2 30 x 92RB26440071051 8.734.5
30 mm Type 5 30 x 1223455007607011.941.1
The Bell XFM-1 Airacuda had remote-controlled 37mm M4 cannon, (right) mounted with a coaxial .30 Browning M2 (left).

The Browning M4 was installed in US fighters such as the P-39 Airacobra and early versions of the P-38 Lightning. This was a slow-firing cannon, with a low muzzle velocity and a limited ammunition capacity, but for its calibre it was light. It was intended to destroy bombers from a distance, but its performance was not sufficient for the task. Nevertheless, Lend-Leased P-39s and P-63s with the M4 gun proved effective medium-altitude fighters on the Eastern Front. 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, and was combined with a higher cyclic rate. This weapon was installed in later models of the P-63 Kingcobra.

A single P-63D was armed with an M9 cannon, a very different weapon, far more powerful but also far heavier. Its 37x223SR cartridge gave the same HE round as the M4 a considerably higher muzzle velocity. One of the types of ammunition available was a 752 g armour-piercing projectile with a muzzle velocity of 930 m/s, and at a distance of 460 m this penetrated 60 mm of armour plate. At the same distance the M4 could penetrate only 20 mm of armour. It is obvious that the M9 was much better suited for ground attack, but apparently it was too heavy for fighters. It was also experimentally used on a number of attack aircraft, but its only service use was at sea. For some reason, maybe because the M4 was known as the T9 before it was officially adopted, the M9 and M4 are often confused.

More bizarrely, a publicity effort by the American Aircraft Co. (AAC) managed to associate itself with cannon-armed USAAF fighters, and it is sometimes named as the manufacturer of the M4. In fact AAC’s cannon was far inferior, and it never seems to have been used in combat by anyone!

The Germans initially developed the MK 101 with the intention of attacking bombers from a safe distance. But its weight and low rate of fire excluded this use; instead it was installed in ground attack aircraft, for example the Hs 129. It was very useful against (lightly) armoured ground targets, firing an AP round with a tungsten core at 960 m/sec. The MK 103 was lighter than the MK 101, 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 carry the MK 103 gun. Installations in the wings tended to be inaccurate, because the enormous recoil twisted the wing; centreline installations as engine cannon were designed for the Ta 152C, Do 335 and Bf 109K, but evidence that this was turned into hardware exists only for the Do 335 and the prototypes of the Ta 152C. The fighter designs that were on German drawing boards in 1945 sometimes made provision for the MK 103, but the favorite weapon was the MK 108.

The MK 108 30-mm aircraft cannon.

The MK 108 was put into service because the fight against Allied heavy bombers required a 30 mm cannon that was compact and light enough to be installed in single-engined fighters. The MK 108 used the APIB operating principle of the Oerlikon guns. It was less than half the weight and bulk of the MK 103, and much cheaper to produce, but it also had a much lower ballistic performance. 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 close to their targets, normally opening fire at 300 m. Its use required strong nerves and better training than German pilots received during these last phases of the war. Some effort was made to increase the rate of fire, and a 850 rpm version was apparently perfected, although too late to be adopted.

The BK 3,7 was used successfully against tanks, most notably by the Ju 87G, firing a 405 g Hartkernmunition with a tungsten core at 1140 m/s. It was also tried in the air as a weapon against heavy bombers, in Bf 110s. Presumably the conventional APHE (680 g) and HE (640 g) munition was used. It was not successful in this role. 

The search for a gun that would destroy a heavy bomber with a single hit produced a series of 55 mm cannon, because these rounds would hold the 450 g of high explosive that was considered to be necessary. As for the 30 mm weapons, the Germans considered both heavy long-range guns, and light guns with a more modest ballistic performance. The advantage of the long-range 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 MK 101 and MG c/30L. As a quick solution, the BK 5 was considered, based on the PAK 38 anti-tank gun. It was light and a good performer by the standards of 50 mm anti-tank cannon, but by the standards of fighter guns it was extremely heavy and slow-firing! It was fed from a closed-loop 22-round belt, and fired 1.54 kg projectiles. It was installed in some Me 410 fighters, but when Allied escort fighters appeared in the German skies these overburned twin-engined aircraft became easy prey. Another interim weapon was the MK 214A, installed only in a single Me 262. Its rate of fire, 160 rpm, was much better than that of the BK 5. Developed from the KwK39/1 tank gun, it still weighed 490 kg. A proposed 55 mm version, the MK 214B, was even heavier.

The light 55 mm cannon was a more realistic weapon. It took the form of the MK 112, in effect a scaled up MK 108. The MK 112 weighed only 274 kg and had a relatively high rate of fire. Because of the lower muzzle velocity, the effective range was much shorter. The MK 112 never went beyond the prototype stage, despite continuation of development post-war in the USA. For such heavy projectiles, rockets proved to be a superior weapon, and the big cannon never entered service.

Russian weapons such as the NS-37 were intended both for air-air combat and for use against ground targets. Usually only a single cannon of this type was carried, typically between the cylinder banks of the Klimov V-12 engines of the Yakovlev fighters.

The first gun in service, in 1940, was the powerful VYa, with a 152 mm 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 40 mm of armour at an angle of up to 40 degrees. The Yak-9T with the NS-37 was quite successful, and 2748 of these fighters were built. Because of the recoil of the gun it was advised to fire thee-round bursts, but a single hit could destroy an aircraft. The Yak-9K carried the large NS-45, an even more powerful weapon which required a large muzzle brake to keep the recoil within acceptable limits. Few Yak-9Ks were built, apparently because the gun was not entirely reliable and a failure could have disastrous consequences. Even larger cannon were tried, but the recoil of the NS-57 was too much for fighters.

From 1945 onwards, the NS-23 was introduced, a development of the NS-37 scaled down to 23 mm. It replaced the much heavier VYa in fighters, but because of the less powerful cartridge was the muzzle velocity was considerably lower. The NS-23 was a more typical fighter weapon, less suitable for ground support missions. It would stay around for a long time.

Late in the war, the Japanese Army had a good 30mm cannon in the Ho-155, sometimes erroneously referred to as Ho-105 or even Ho-151. It was a scaled-up derivative of the Ho-5, itself a derivative of the Browning. Late in the war, the Ho-155 appeared on bomber destroyer versions of some of the best Japanese Army fighters, such as the Ki-61 and Ki-84, but it seems to have seen little combat use. The gun compares favourably with the German MK 108. At the end of the war a lighter, shorter version was developed, the Ho-155-II, but this version never saw combat. It was a far cry from the early days of the war, when most Japanese Army fighters were armed with two rifle-calibre machineguns!

The Japanese Army installed even bigger cannon in twin-engined fighters, developments of the Ki-45 Toryu, but these were unimpressive weapons. A first attempt was made to install the Type 94, a hand-loaded 37 mm weapon originally used in tanks. The achievable rate of fire was about 15 rpm. The automatic Ho-203, with a 15-round closed-loop belt, was a much-needed improvement. Apparently it was designed for single-shot firing, hence its low rate of fire. References to the use of the Ho-203 on single-engined fighters, such as the Ki-44, can not be correct, because of the enormous bulk of this gun. They could refer to the Ho-204, another enlargement of the Browning, that appeared in 1944. It was adopted in some experimental twin-engined fighters, and saw service as an upward-firing gun in the Ki.46-III-KAI.

The 57 mm Ho-401 was an enlarged Ho-203, with a similar 15-round closed-loop belt and low rate of fire. It was used mainly for anti-armour and anti-shipping attacks, but occasionally it was used against B-29 bombers as well, because the Japanese did not have any better defense against the B-29. A desperate measure was the installation of the 75 mm Type 88 anti-aircraft gun in a Ki-67 bomber, to create the Ki-109 “fighter”. It seems obvious that this was a bad idea, especially as the gun itself was rather mediocre, and without the planned but never available turbosuperchargers the Ki-109 could not even get close to the B-29s. Nevertheless the Japanese did not abandon 75 mm cannon, and development of the Ho-501, a 75 mm version of the Ho-203, seems to have been completed at the end of the war.

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 150 m, but because there was no need to extract the case and eject it, the rate of fire was fairly high for a gun in this calibre. It was also light. This gun armed some models of the Ki-44 single-seat fighter.

The Japanese Navy also showed interest in 30 mm cannon. The Type 2 was a scaled-up Oerlikon gun, sometimes erroneously described as a copy of the MK 108. It never became a standard service weapon, although it was tested on a number of aircraft and formally adopted. A better alternative was available, the Type 5, an entirely original design. Though fairly heavy, this was a powerful weapon with a good performance. If the war had laster longer, it would have become the standard weapon, fitted in fighters such as the Kyushu J7W Shiden. But it saw service in only a few aircraft, being wing-mounted in the Mitsubishi J2M5 and installed in upward-firing installations on some nightfighters, such as the P1Y2-S.

Next: Ammunition