Postscript

Post-War Fighter Guns

The first jet fighters were developed during WWII: The Heinkel He 280, Messerschmitt Me 262, Heinkel He 162, Gloster Meteor, de Havilland Vampire, Lockheed P-80, and McDonnell FH Phantom. Their advantages were so obvious that only a handful of propeller-driven fighters entered service after the war.

Jet fighters brought higher speeds, and that in itself made gun aiming more difficult. The structure of the aircraft became sturdier, with thicker skins. All this increased the need for powerful armament. On the other hand radar equipment, better gunsights and head-up displays promised to make guns far more accurate. At first the electronics systems were maintenance-intensive and poorly suited to the stress of combat, but the sophistication of today's aircraft is such that any round fired has a high probability to hit the target.

Five people at work in one picture: There can be no doubt that this was posed. But it does show how the four Hispano cannon were installed in the nose of a Meteor. [4]

The armament of the first jet fighters was the same as that of the last piston-engine fighters. There was only a change in armament installation: Most jet fighters had their guns in the nose. Installing guns in the nose instead of the wings gave concentrated fire at a wide range of distances. The nose also offered more room than the wings, which were being made thinner to reach higher speeds. And putting the guns in front helped to balance the weight of the jet engine in the tail. A problem, especially for night operations, is the muzzle flash, that might blind the pilot temporarily.

While Germany of course did not design post-war military aircraft, it is interesting to have a look at the designs that were on the drawing boards in 1945. These were eagerly studied by the victorious allies, and inspired many post-war aircraft. The Luftwaffe initially demanded that the replacement of the Me 262 would be a high-altitude jet fighter capable of 1000km/h between 7000m and 9000m, and with an endurance of 60 minutes at full throttle. The pilot had to be put in a pressure cabin, with sufficient armour to stop .50 ammunition. Initially, the Luftwaffe was satisfied with two 30mm MK 108 cannon. But it quickly upgraded its demands to four MK 108 cannon, and two hours endurance. The proposals were all swept-wing jet fighters. Alternatives to the four MK 108 cannon proposed by the designers included two MK 103 and two MG 151/20 cannon, or two MG 213C revolver cannon.

The MG 213C was designed in 1944, and it was a revolver gun with a five-chamber cylinder. By dividing the loading of a cartridge in three steps, a high rate of fire could be achieved while keeping the forces within the gun limited. There were 20mm and 30mm versions. The MG 213C made linear action guns obsolete for fighters, and was copied widely.

Aircraft Cannon Data.
Russian Aviation Gunnery Page.
IZMASH Page.

In Britain the armament of four 20mm Hispano cannon remained the standard. The Meteor had actually been designed for six such cannon, but the mount of two of them was too unpractical to be safely used. Four 20mm cannon were carried by the last piston-engined fighters and the straight-wing jet fighters. The Hispano remained in use until the first swept-wing fighters appeared with the 30mm Aden cannon, a copy of the MG 213C. With four Aden guns, the Hawker Hunter was considered over-gunned by many observers: A rare distinction for any fighter aircraft. Two Aden guns, as in the Lightning, Jaguar, Saab J35 Draken, and Folland Gnat, was a more common armament.

The evolution in France was almost identical to that in Britain, except that the Hispano was not replaced by the Aden but by the DEFA, a French derivative of the MG 213C. The Aden and DEFA guns initially used slightly different ammunition, but later common ammunition was introduced, creating a de facto standard for 30mm rounds. Because of the successful export of French aircraft, the DEFA gun is still used world-wide. The later developments had an increased rate of fire (up to 1800 rpm) and are fitted to modern fighters such as the Mirage 2000.

Sweden adopted the Swiss 30mm Oerlikon KCA, a very powerful revolver cannon, for the Saab JA 37 Viggen interceptor. It is relatively slow-firing, but has excellent ballistics and it has been estimated that its ammunition has twice the destructive power of the Aden/DEFA ammunition of the same calibre.

The US Navy initially followed the British example. This had already begun during the war, with types such as the F4U-1C and F8F-1B. Its first jet fighters almost all had four 20mm Hispano cannon, for example the FH Phantom, F2H Banshee, and F9F Panther. The M3 version of this gun was boosted to 850rpm. Like the Hispano Mk.V, it had been lightened by shortening the barrel, in this case by 15in. The USN was unusual in that it continued the use of these weapons on swept-wing fighters and right into the supersonic age, although in an upgraded version: The Colt Mk.12. The Mk.12 fired a lighter projectile with a larger charge. But on the Navy's Mach 2 fighter, the Vought F8U Crusader, the Colt guns were an anachronism. They had a good rate of fire and a high muzzle velocity, but were inaccurate, unreliable, and unpopular. But the F8U at least had guns, and they contributed to the good reputation that this fighter acquired in Vietnam. No gun was installed on the F-4 Phantom II, in the belief that the new guided missiles made gun obsolete. And the weight, bulk and vulnerability of the electronics required for their use made it attractive to save weight by leaving the guns out. Experience in Vietnam indicated that it was still highly desirable to have a gun, and currently USN fighters are equipped with the six-barrel M61 Vulcan.

Russian Aviation Gunnery Page.
IZMASH Page.
Aircraft Cannon Data.

The USAF was even more conservative. In the late 1940s the standard armament of USAF fighters, with only few exceptions, was still six Browning .50 M3 guns. It was faster-firing than the M2 version used in WWII, but experience in Korea demonstrated that this armament was painfully insufficient. A report by Colonel Eagleston estimated that two thirds of all MiG-15s hit with the .50 guns escaped. On the other side it was observed that MiG-15s with 40 or 50 hits routinely returned home. The American pilots still held the advantage, because of better training, better gunsights, and generally better equipment.

In some nightfighters and fighter-bombers the USAF installed the 20mm M24 cannon, a version of the Hispano M3 of the US Navy, modified to use electrically primed ammunition. The first versions of the F-89 Scorpion, for example, carried six of these guns. The F-86K carried four.

Left, for testing six M24 Hispano cannon were installed in a mock-up of the nose of the XF-88. [12]

A much-needed improvement was the Pontiac M39, a 20mm revolver cannon broadly based on the MG 213C, but almost entirely redesigned. This far better weapon was installed on fighters such as the F-86H Sabre, F-100 Super Sabre, and Northrop F-5. A switch to 30mm cannon was considered, but rejected in the belief that guided missiles would soon make the cannon obsolete. Apparently, two F-89C protototypes were the only US fighters that ever carried 30mm cannon.

The F-4 and F-106 appeared without cannon, but like the USN the USAF had to change its mind because of combat experience, and during the Vietnam war cannon were installed in these fighters. The standard weapon became the six-barrel M61 Vulcan, and it is still in use today, usually in its M61A1 form. The M61 was the first rotary cannon, generally (and not entirely correct) called a Gatling gun. Such weapons are reliable and offer a very high rate of fire, and by dividing the firing over several barrels their wear is reduced. Of course such guns weigh more than single-barrel weapons. Characteristic of the M61A1, and most US rotary cannon, is the beltless feed mechanism: Rounds are transported on a kind of conveyer belt system, and empty cases are transported back into the drum. The original M61 had a belt feed, but this could not take the strain of firing rates higher than 4000 rpm.

An objection raised against rotary cannon is that the spin-up time is fairly long: It takes 0.4 sec before the M61A1 spins up to its nominal rate of fire, while a revolver gun reaches its nominal rate of fire after 0.05 sec. Hence the advantage of the rotary cannon is minimal or non-existent during a short burst.

Description of the M61 on 3-4-9, the F-16 reference page.
The USAF museum has an M61 Vulcan.
Russian Aviation Gunnery Page.
Aircraft Cannon Data.

Left, the N-37. [13]

The Soviet Union was more reluctant to abandon its guns, and it indeed developed a surprisingly large number of new ones in the post-war years. Apparently the USSR was reluctant to copy the MG 213C. It did show a preference for large-calibre weapons, with calibres up to 57mm proposed for installation in fighters. In these early years of the Cold War only the USA had nuclear weapons, and the only means to deliver these bombs was the B-29 or B-50 bomber. Hence Soviet fighters were given armament sufficiently powerful to shoot down B-29s. The first Soviet jet fighter, the MiG-9, was designed for two 23mm NS-23 cannon and one 57mm N-57, but the latter was replaced by the less ponderous 37mm N-37 before the aircraft flew. This was essentially a lighter, less powerful development of the NS-37. Soviet designers estimated that it would take eight 23mm shells, or two 37mm shells, to destroy a B-29. The same armament was retained by the MiG-15, except that the NS-23 was soon replaced by the faster-firing NR-23. In Korea it was shown that this armament, though powerful, was stuck in a fighter that was a poor gun platform and had primitive gunsight. However, the much-improved MiG-17, with the same armament, was very effective in Vietnam.

The supersonic MiG-19 abandoned the N-37. Initial deliveries had two NR-23 cannon, but the standard weapon was the NR-30, basically a scaled-up NR-23. But for its first generation of Mach 2 fighters, the Su-9 and MiG-21, the USSR too abandoned guns. On all-round fighters they soon returned. The twin-barrel GSh-23 guns were installed on the MiG-21 and the MiG-23. This weapon uses the Gast principle, named after its inventor Carl Gast, who developed it in Germany during WWI. In these guns, the firing of one barrel drives the action of the other half of the gun.

Modern Fighter Guns

The choice for modern fighters is generally between revolver guns and rotary guns. The former are lighter and fire more rounds in a short burst, the latter have a higher sustained rate of fire.

In Britain a new version of the Aden was developed, the Aden 25, that fires the NATO standard 25mm ammunition. This has been adopted for the latest British versions of the Harrier, two being installed in underfuselage packs. US versions of the same aircraft fire the same ammunition, but they have a single rotary gun, the five-barrel GAU-12 Equaliser.

But for the RAF's next generation fighter, the gun is provided by Germany. For European aircraft projects, including the Tornado and the Eurofighter, the Mauser BK 27 was developed. This 27mm revolver cannon is a new design. No attempt was made to use existing ammunition, and the 27mm calibre is unique. The BK 27 was also adopted for the Swedish JAS 39 Gripen. It has been considered to develop a multi-barrel version of this gun for Eurofighter, but this plan seems to have been abandoned.

The French stepped out of the Eurofighter project. Their next-generation fighter is the Rafale, and a new gun has been developed for it: The GIAT 30/791. This is one of the fastest-firing single-barrel guns, thanks to the use of a seven-chamber cylinder.

Current Soviet fighters are armed with the six-barrel GSh-6-23 and GSh-6-30, or with the single-barrel GSh-30-1. The MiG-31 has the very fast-firing GSh-6-23. This is probably the fastest-firing gun in use, and the manufacturer claims rates of fire as high as 10000 to 12000 rpm for this gun! The GSh-6-30 was used on the MiG-27, for ground support missions. But apparently the GSh-30-1 is preferred for the MiG-29 and Su-27 because of its greater destructive power and lower weight. The GSh-30-1 is unique, because it is the only linear action gun used in a modern fighter. Its rate of fire is similar to that of a revolver cannon, and the GSh-30-1 is considerably lighter. And while its muzzle velocity is modest by modern standards, its accuracy is reported to be very good.

The USAF and USN again show conservatism. Development of the new 25mm GAU-7 gun using caseless ammunition was abandoned, and the old M61 is still the main fighter gun. Some effort has been made to reduce the weight of the gun, and a version weighing 93kg is under development. This also decreases spin-up time. The disadvantage of the M61 is now the relatively small killing power of its ammunition: Other nations have now adopted larger calibre guns, that fire rounds two or three times heavier than the M50 ammunition of the Vulcan. These 20mm rounds are still the same size as that adopted for the M39s in the 1950s, and at time deemed acceptable in the belief that guns would soon become obsolete!

The table below gives the firepower parameters of some modern fighters. Note that the apparent advantage of rotary guns in rate of fire would decrease if short bursts are fired, because of their longer spin-up time. Data for the number of rounds fired in the first second by the M61A1 vary from 47 to 72.

This can be compared with the data for WWII Fighters. At the end of WWII, the best fighters had an armament firing about 5kg/sec. All modern fighters are well above that, but the difference is smaller than one would expect. The reason is the decreased importance attached to guns in modern air combat, as missiles are now the primary weapon. The is less pressure to improve firepower than there used to be. This is particularly obvious for US fighters: If only the guns are taken into account, the F-22 will have slightly less firepower than the F-100 Super Sabre!

Next: Korean War Fighters