M61 Vulcan
The United States Air Force became a separate branch of the military in 1947. This new branch issued a request for a new aircraft gun to replace older models like the P-51 and P-47. These earlier fighters used .50 caliber (12.7 mm) main armament that required pilots to get dangerously close to enemy aircraft. The Hispano cannon carried by the P-38 had a relatively low rate of fire for the jet age. European designers were moving towards heavier weapons, but the U.S. initially concentrated on a powerful cartridge designed for a pre-war anti-tank rifle. In 1946, the Army issued General Electric a contract for Project Vulcan. This six-barrel weapon was capable of firing 7,200 rounds per minute. The first GE prototypes of the T45 caliber were ground-fired in 1949. They achieved 2,500 rpm, which increased to 4,000 rpm by 1950. Air combat experience in the Korean War led the USAF to test alternatives based on the 20mm caliber cartridge. These variants were known as the T171 and T150 respectively and were first tested in 1952. Eventually, the standard 20×102 mm cartridge was determined to have the desired balance of projectile/explosive mass and muzzle velocity.
Each of the cannon's six barrels fires once in turn during each revolution of the barrel cluster. The multiple barrels provide both a very high rate of fire, around 100 rounds per second, and contribute to prolonged weapon life by minimizing barrel erosion and heat generation. Most aircraft versions of the M61 are hydraulically driven and primed electrically. The gun rotor, barrel assembly and ammunition feed system are rotated by a hydraulic drive motor through a system of flexible drive shafts. The round is fired by an electric priming system where an electric current from a firing lead passes through the firing pin to the primer as each round is rotated into the firing position. The self-powered version, the GAU-4 (called M130 in Army service), is gas-operated. It taps gun gas from three of the six barrels to operate the gun gas-driven mechanism. The initial M61 used linked ammunition, but the ejection of spent links created considerable problems. The original weapon was soon replaced by the M61A1, with a linkless feed system. Depending on the application, the feed system can be either single-ended or double-ended. A disadvantage of the M61 is that the bulk of the weapon, its feed system, and ammunition drum make it difficult to fit it into a densely packed airframe.
Until the late 1980s, the M61 primarily used the M50 series of ammunition in various types. These rounds typically fired a projectile at a muzzle velocity of about 1,020 meters per second. A new PGU-28/B round was developed in the mid-1980s. It is a semi-armor-piercing high-explosive incendiary round providing improvements in range, accuracy, and power over the preceding M56A3 HEI round. The PGU-28/B has not been without problems. A 2000 USAF safety report noted 24 premature detonation mishaps causing serious damage in many cases over 12 years. This compared to only two such mishaps in the entire recorded history of the M56 round. The report estimated that the PGU-28/B had a potential failure rate 80 times higher than USAF standards permit. Due to safety issues, it was limited to emergency wartime use in 2000. Practically no powered rotary cannon is supplied with sufficient ammunition for a full minute of firing due to its weight. At 6,000 rpm, the projectiles alone would represent a mass of about 12 kilograms for one minute of firing.
The Vulcan was first used in aerial combat on the 4th of April 1965. Four North Vietnamese Vietnam People's Air Force MiG-17s attacked a force of 10 North American F-100 Super Sabres escorting 48 Vulcan-armed and bomb-laden F-105 Thunderchiefs. The MiG leader and only survivor from the four MiGs, Captain Tran Hanh, reported that U.S. jets had pursued them. He stated that F-105s had shot down three of his aircraft, killing lieutenants Pham Giay, Le Minh Huan and Tran Nguyen Nam. The first confirmed Vulcan gun kill occurred on the 29th of June 1966 when Major Fred Tracy fired 200 rounds of 20 mm into a MiG-17. This happened after the VPAF MiG flew in front of him following a pass where it had just fired a 23 mm shell which entered one side of his cockpit and exited the other. A table of combat kills shows 39 total MiG-17s destroyed by the M61A1 between 1966 and 1972. Another six MiG-21s were also recorded as destroyed during this period.
The gun was installed in the Air Force's A-7D version of the LTV A-7 Corsair II where it replaced the earlier United States Navy A-7's Colt Mk 12 cannon. It was integrated into the newer F-4E Phantom II variants. The F-4 was originally designed without a cannon because missiles were believed to have made guns obsolete. Combat experience in Vietnam showed that an internal gun could be more effective than guided missiles or externally carried gun pods. The improved pods were self-powered and properly synchronized to the sights, while USAF versions of the F-4 were hastily fitted with internal M61 cannons in a prominent fairing under the nose before the war ended. The next generation of fighters built post-Vietnam incorporated the M61 gun internally. Other aircraft include the Italian/Brazilian AMX International AMX on Italian aircraft only, and the F-22 Raptor. Two gun pod versions, the SUU-16/A and improved SUU-23/A, were developed in the 1960s often used on gless versions of the F-4. Both pods contained 1,200 rounds of ammunition with a loaded weight of approximately 50 kilograms.
The M61 was originally produced by General Electric. After several mergers and acquisitions, it is now produced by General Dynamics. It is also manufactured under license in Japan by Sumitomo Heavy Industries for Japan's Self-Defense Force. SNT Dynamics manufactures the weapon in South Korea as well. A lighter version of the Vulcan developed for use on the F-22 Raptor, designated M61A2, is mechanically the same as the M61A1 but with thinner barrels to reduce overall weight. The rotor and housing have been modified to remove any piece of metal not absolutely needed for operation. On the 13th of December 2024, the Ukrainian Air Force claimed an F-16 shot down six Russian cruise missiles using the M61 Vulcan 20 mm cannon. The pilot stated that a few bursts from the cannon caused explosions followed by secondary detonations. The M61 is also the basis of the US Navy Mk 15 Phalanx close-in weapon system and the M163 VADS Vulcan Air Defense System.
Continue Browsing
Common questions
When was the M61 Vulcan first used in aerial combat?
The M61 Vulcan was first used in aerial combat on the 4th of April 1965. This engagement involved North Vietnamese MiG-17s attacking a force of F-100 Super Sabres and F-105 Thunderchiefs.
Who manufactured the M61 Vulcan originally and who makes it now?
General Electric originally produced the M61 Vulcan before General Dynamics took over production following several mergers and acquisitions. Sumitomo Heavy Industries manufactures the weapon under license for Japan's Self-Defense Force, while SNT Dynamics produces it in South Korea.
What is the rate of fire for the M61 Vulcan cannon?
The M61 Vulcan fires at a rate of approximately 100 rounds per second or 6,000 rounds per minute. The six barrels rotate to provide this high volume of fire while minimizing barrel erosion and heat generation.
How many MiG aircraft were destroyed by the M61A1 between 1966 and 1972?
Combat records show that 39 total MiG-17s and another six MiG-21s were destroyed by the M61A1 between 1966 and 1972. The first confirmed gun kill occurred on the 29th of June 1966 when Major Fred Tracy fired into a MiG-17.
When did the Ukrainian Air Force claim an F-16 shot down Russian cruise missiles using the M61 Vulcan?
On the 13th of December 2024, the Ukrainian Air Force claimed an F-16 shot down six Russian cruise missiles using the M61 Vulcan 20 mm cannon. The pilot stated that bursts from the cannon caused explosions followed by secondary detonations.