| M61 Vulcan | |
|---|---|
 An unmounted M61A1 Vulcan withflash suppressor used in the SUU-16/A gun pod | |
| Type | Rotary cannon |
| Place of origin | United States |
| Service history | |
| In service | 1959–present |
| Used by | United States, someNATO members,Japan,South Korea,Saudi Arabia, and others |
| Wars | |
| Production history | |
| Designer | General Electric |
| Designed | 1946 |
| Manufacturer | General Dynamics Sumitomo Heavy Industries SNT Dynamics |
| Variants | See below |
| Specifications | |
| Mass |
|
| Length | 71.93 in (1.827 m) |
| Barrel length | 59.8 in (1.52 m) |
| Cartridge | 20×102mm Vulcan |
| Caliber | 20 mm (0.787 in) |
| Barrels | 6-barrel (progressive RH parabolic twist, 9 grooves) |
| Action | Hydraulically operated, electrically fired,rotary cannon |
| Rate of fire | 6,000 rounds per minute[1] |
| Muzzle velocity | 3,450 ft/s (1,050 m/s) with PGU-28/B round |
| Effective firing range | About 9,842 ft (3,000 m) |
| Feed system | Belt or linkless feed system |
TheM61 Vulcan is ahydraulically, electrically, orpneumatically driven, six-barrel, air-cooled, electrically firedGatling-stylerotary cannon which fires20 mm × 102 mm (0.787 in × 4.016 in) rounds at an extremely high rate (typically 6,000 rounds per minute). The M61 and its derivatives have been the principal cannon armament ofUnited States militaryfixed-wing aircraft for over sixty years.[2]
The M61 was originally produced byGeneral Electric. After several mergers and acquisitions, it is produced byGeneral Dynamics as of 2000[update].[2] It is also manufactured under license in Japan bySumitomo Heavy Industries for Japan'sSelf-Defense Force[3] and bySNT Dynamics in South Korea.[4]
At the end ofWorld War II, theUnited States Army Air Forces began to consider new directions for futuremilitary aircraft guns. The higher speeds ofjet-poweredfighter aircraft meant that achieving an effective number of hits would be extremely difficult without a much higher volume of fire. While captured German designs (principally theMauser MG 213C) showed the potential of the single-barrelrevolver cannon, the practical rate of fire of such a design was still limited by ammunition feed and barrel wear concerns. The Army wanted something more advanced, combining an extremely high rate of fire with exceptional reliability.[5]
In 1947, theAir Force became a separate branch of the military. The new Air Force made a request for a new aircraft gun. A lesson of World War II air combat was that German, Italian, and Japanese fighters could attack American aircraft from long range with their cannon main armament. American fighters with.50 caliber (12.7 mm) main armament, such as theP-51 andP-47, had to be close to enemy aircraft in order to hit and damage them. The20 mm (0.79 in) Hispano cannon carried by theP-38 andP-61, while formidable against propeller-driven planes, had a relatively low rate of fire in the age of jets, while other cannons were notoriously unreliable.
In response to this requirement, the Armament Division of General Electric resurrected an old idea: the multi-barrelGatling gun. The original Gatling gun had fallen out of favor because of the need for an external power source to rotate the barrel assembly, but the new generation of turbojet-powered fighters offered sufficientelectric power to operate the gun, and electric operation was more reliable thangas-operated reloading.[6]
With multiple barrels, the rate of fire per barrel could be lower than a single-barrel revolver cannon while providing a greater overall rate of fire. The idea of powering a Gatling gun from an external electric power source was not a novel idea at the end of World War II, asRichard Jordan Gatling himself had done just that with a patent he filed in 1893.[7]
DuringWorld War I, a similar 12-barreledFokker-Leimberger aircraft rotary machine gun, powered by either the aircraft engine or an electric motor, had been under development by theGerman Empire.[citation needed]
In 1946, the Army issued General Electric a contract for "Project Vulcan", a six-barrel weapon capable of firing 7,200 rounds per minute (rpm).[8] Although European designers were moving towards heavier 30 mm (1.181 in) weapons for better hitting power, the U.S. initially concentrated on a powerful 0.60-inch (15 mm) cartridge designed for a pre-war anti-tank rifle, expecting that the cartridge's highmuzzle velocity would be beneficial for improving hit ratios on high-speed targets.[5] The first GE prototypes of the 0.60-inch (15 mm) caliber T45 were ground-fired in 1949; it achieved 2,500 rpm, which was increased to 4,000 rpm by 1950. Due to air combat experience in theKorean War, the USAF decided that high velocity alone might not be sufficient to ensure target destruction and tested 20 and 27 mm (0.787 and 1.06 in) alternatives based on the 0.60-inch (15 mm) caliber cartridge. These variants of the T45 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, resulting in an optimum balance of range, accuracy and kinetic energy on target.[9]
The development of theLockheed F-104 Starfighter revealed that the T171 Vulcan (later redesignatedM61) suffered problems with itslinked ammunition, being prone to misfeed and presenting aforeign object damage hazard with discarded links. A linkless ammunition feed system was developed for the upgradedM61A1, which subsequently became the standard cannon armament of U.S. fighters.[10]
In 1993,General Electric sold its aerospace division, including GE Armament Systems along with the design and production tooling for the M61 and GE's other rotary cannon, toMartin Marietta. After Martin's merger withLockheed, the rotary cannon became the responsibility of Lockheed Martin Armament Systems. Lockheed Martin Armament Systems was later acquired byGeneral Dynamics, which produces the M61 and its variants as of 2000[update].[2]
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.[11] The average time between jams or failures is in excess of 10,000 rounds, making it an extremely reliable weapon.[12] The success of the Vulcan Project and its progeny, the very-high-speed Gatling gun, has led to guns of the same configuration being referred to as"Vulcan cannons", which can sometimes confuse nomenclature on the subject.
Most aircraft versions of the M61 are hydraulically driven and electrically primed. 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.[13]
The self-powered version, the GAU-4 (called M130 in Army service), isgas-operated, tapping gun gas from three of the six barrels to operate the gun gas-driven mechanism. The self-powered Vulcan weighs about 4.5 kilograms (10 lb) more than its electric counterpart, but requires no external power source to operate, except for an electric inertia starter to initiate gun rotation, allowing the first rounds to be chambered and fired.[13]
The initial M61 used linked ammunition, but the ejection of spent links created considerable (and ultimately insuperable) 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 (ejecting spent cases and unfired rounds) or double-ended (returning casings back to the magazine). 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.[14]
The feed system must be custom-designed for each application, adding 140 to 180 kg (300 to 400 lb) to the complete weapon. Most aircraft installations are double-ended, because the ejection of empty cartridges can cause a foreign-object damage hazard for jet engines and because the retention of spent cases assists in maintaining the center of gravity of the aircraft.[15] The first aircraft to carry the M61A1 was the C model of theF-104, starting in 1959.[16]
A lighter version of the Vulcan developed for use on theF-22 Raptor, designated M61A2, is mechanically the same as the M61A1, but with thinner barrels to reduce overall weight to 92 kilograms (202 lb). The rotor and housing have also been modified to remove any piece of metal not absolutely needed for operation and replaces some metal components with lighter-weight materials. TheF/A-18E/F Super Hornet also uses this version.[17]
The Vulcan's rate of fire is typically 6,000 rounds per minute, although some versions (such as that of theAMX and theF-106 Delta Dart) are limited to a lower rate, and others (A-7 Corsair,F-15 Eagle) have a selectable rate of fire of either 4,000 or 6,000 rounds per minute. The M61A2's lighter barrels allow a somewhat higher rate of fire, up to 6,600 rounds per minute.[18]
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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 600 kg (1,300 lb) for one minute of firing; and by including the brass shell, filling and primer the weight is slightly double that at 1,225 kg (2,701 lb)). In order to avoid using the 600 to 1,000 rounds carried by aircraft all at once, a burst controller is generally used to limit the number of rounds fired at each trigger pull. Bursts of from two or three up to 40 or 50 can be selected.[19] The size of the airframe and available internal space limits the size of the ammunition drum and thus limits the ammunition capacity. When vehicle-mounted, the only limiting factor is the vehicle's safe carry weight, so commensurately larger ammo storage is available.
Until the late 1980s, the M61 primarily used the M50 series of ammunition in various types, typically firing a 99-gram (3.5 oz) projectile at amuzzle velocity of about 1,030 metres per second (3,380 ft/s). A variety of armor-piercing incendiary (API), high-explosive incendiary (HEI), and training rounds are available.
A new PGU-28/B round was developed in the mid-1980s. It is asemi-armor-piercing high-explosive incendiary (SAPHEI) round, providing improvements in range, accuracy, and power over the preceding M56A3 HEI round.[20] The PGU-28/B is a "low-drag" round designed to reduce in-flight drag and deceleration, and has a slightly increased muzzle velocity of 1,050 metres per second (3,450 ft/s).[21] However, 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) in 12 years with the SAPHEI round, 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.[22] Due to safety issues, it was limited to emergency wartime use in 2000.[23]
The main types of combat rounds and their main characteristics are listed in the table:
| Designation | Type | Projectile weight [grains] | Bursting charge [grains] | Muzzle velocity [m/s] | Description |
|---|---|---|---|---|---|
| M53 | API | ? | 65 gr (4.2 g; 0.15 oz) incendiary[24] | 1,030 | 6.4 mm (0.25 in)RHA penetration at 0 degree impact angle and 1,000 m (3,300 ft) range.[24] |
| M56A3/A4 | HEI | 1,543 gr (100.0 g; 3.5 oz)[24] | 165 gr (10.7 g; 0.38 oz) HE and 20 gr (1.3 g; 0.046 oz) incendiary[24] | 1,030 | Nose fuzed round, no tracer. 2 m (6.6 ft) effective radius to produce casualties to exposed personnel.[24] Fragmentation hazard out to 20 m (66 ft).[25] 12.7 mm (0.50 in) RHA penetration at 0 degree obliquity at 104 m (341 ft) range.[24] |
| PGU-28A/B | SAPHEI | 1,580 gr (102.4 g; 3.6 oz)[20] | 150 gr; 0.35 oz (10 g)[25] | 1,050 | Multi-purpose fuzeless round with an incendiary charge in the nose setting off the HE behind it with a slight delay to maximize lethality against aircraft. No tracer or self-destruct. Azirconium pellet at the bottom of the HE cavity provides additional incendiary effect. |
The Vulcan was first used in aerial combat on 4 April 1965, when fourNorth VietnameseVietnam People's Air Force (VPAF)MiG-17s)[26] attacked a force of 10North American F-100 Super Sabres (two of which were assigned weather reconnaissance duties) escorting 48 Vulcan-armed and "bomb-laden"F-105 Thunderchiefs, shooting down two of the latter. The MiG leader and only survivor from the four MiGs, Captain Tran Hanh, reported that U.S. jets had pursued them and that F-105s had shot down three of his aircraft, killing lieutenants Pham Giay, Le Minh Huan and Tran Nguyen Nam. Captain Donald Kilgus, piloting an F-100, received an official probable kill with his fourM39 20 mm cannons during the engagement; however no other US pilot reported destroying any MiGs during the battle, leaving open the possibility that at least two of the MiG-17s may have been downed by their ownanti-aircraft fire.[27][28][29]
The first confirmed Vulcan gun kill occurred on 29 June 1966 whenMajor Fred Tracy, flying his F-105 with the 421st TFS, fired 200 rounds of 20 mm into a MiG-17 that had just fired a 23 mm shell which entered one side of his cockpit and exited the other. When the VPAF MiG flew in front of him after making its pass, Tracy opened fire on it.[30][31]
The gun was installed in the Air Force's A-7D version of theLTV A-7 Corsair II where it replaced the earlierUnited States Navy A-7'sColt Mk 12 cannon and was adopted by the Navy on the A-7C and A-7E.[32] It was integrated into the newerF-4E Phantom II variants. The F-4 was originally designed without a cannon as it was believed that missiles had made guns obsolete. Combat experience in Vietnam showed that a gun could be more effective thanguided missiles in many combat situations and that an externally carried gun pod was less effective than an internal gun; the first generation of gun pods such as the SUU-16 were not oriented with the sights of the fighter. The improved pods were self-powered and properly synchronized to the sights, while the USAF versions of the F-4 were hastily fitted with internal M61 cannons in a prominent fairing under the nose, well before the war ended (Navy Phantoms never received cannons, continuing to rely on air-to-air missiles alone).The next generation of fighters built post-Vietnam incorporated the M61 gun internally.[33][34][35][36]
| Date/year | Firing aircraft | M61 Vulcan variant | Aircraft downed | USAF unit/comments | |
|---|---|---|---|---|---|
| 29 June 1966 | F-105D Thunderchief | M61A1 | MiG-17 | 421st Tactical Fighter Squadron[38] | |
| 18 August 1966 | F-105D | M61A1 | MiG-17 | 34th TFS | |
| 21 September 1966 | F-105D | M61A1 | MiG-17 | 333rd TFS | |
| 21 September 1966 | F-105D | M61A1 | MiG-17 | 421st TFS | |
| 4 December 1966 | F-105D | M61A1 | MiG-17 | 469th TFS | |
| 1967 | F-105D/F-105F | M61A1 | (5) MiG-17s | 333rd TFS | |
| 1967 | F-105D | M61A1 | (8) MiG-17s | 354th TFS | |
| 1967 | F-105D/F-105F | M61A1 | (4) MiG-17s | 357th TFS | |
| 1967 | F-4C Phantom II | SUU-16 gunpod | (2) MiG-17s | 480th TFS | |
| 13 May 1967 | F-105D | M61A1 | MiG-17 | 44th TFS | |
| 3 June 1967 | F-105D | M61A1 | MiG-17 | 13th TFS: Captain Ralph Kuster[39] | |
| 23 August 1967 | F-105D | M61A1 | MiG-17 | 34th TFS | |
| 24 October 1967 | F-4D | SUU-23 gunpod | MiG-21 | 433rd TFS | |
| 1967 | F-4D | SUU-23 | (3) MiG-17s | 435th TFS | |
| 3 January 1968 | F-4D | SUU-23 | MiG-17 | 433rd TFS; pilot, Major B J Bogoslofski,WSO, Captain Richard L Huskey[40] | |
| 14 February 1968 | F-4D | SUU-23 | MiG-17 | 555th TFS | |
| 1972 | F-4E | M61A1 | (3) MiG-21s | 35th TFS; the F4E was the first Phantom II to enter the war with an internal Vulcan gun.[41] | |
| 2 June 1972 | F-4E | M61A1 | MiG-19 | 58th TFS; first kill atsupersonic speed (Mach 1.2); Major Phil Handley/WSO 1LT J. J. Smallwood[42] | |
| 9 September 1972 | F-4E | M61A1 | MiG-21 | 555th TFS | |
| 15 October 1972 | F-4E | M61A1 | MiG-21 | 307th TFS | |
| Total MiG-17s | 32 | ||||
| Total MiG-19s | 1 | ||||
| Total MiG-21s | 6 | ||||
| Total | 39 | ||||
The Vulcan was later fitted into the weapons bay of someConvair F-106 Delta Dart andGeneral Dynamics F-111 Aardvark models. It was also adopted as standard in the "teen"-series air superiority fighters: theGrumman F-14 Tomcat, theMcDonnell Douglas F-15 Eagle,General Dynamics F-16 Fighting Falcon, andMcDonnell Douglas F/A-18 Hornet. Other aircraft include the Italian/BrazilianAMX International AMX (on Italian aircraft only), and theF-22 Raptor. It was fitted in a side-firing installation on theFairchild AC-119 and some marks of theLockheed AC-130gunships, and was used in the tail turrets of both theConvair B-58 Hustler andBoeing B-52H Stratofortress bombers.[i] Japan'sMitsubishi F-1 carried one internally mounted JM61A1 Vulcan with 750 rounds.[32]
Twogun pod versions, theSUU-16/A (also designated M12 by the US Army) and improvedSUU-23/A (US Army M25), were developed in the 1960s, often used on gunless versions of the F-4. The SUU-16/A uses the electric M61A1 with aram-air turbine to power the motor. This proved to cause seriousaerodynamic drag at higher speeds, while speeds under 640 kilometres per hour (400 mph) did not provide enough airflow for the maximum rate of fire.[43]
The subsequent SUU-23/A uses the GAU-4/A self-powered Vulcan, with an electric inertia starter to bring it up to speed. Bothpods ejected empty cases and unfired rounds rather than retaining them. Both pods contained 1,200 rounds of ammunition, with a loaded weight of 733 and 780 kilograms (1,615 and 1,720 lb) respectively. During service in theVietnam War, the pods proved to be relatively inaccurate: the pylon mounting was not rigid enough to prevent deflection when firing, and repeated use would misalign the pod on its pylon, making matters worse.[citation needed]
A variant with much shorter barrels, designated the M195, was also developed for use on theM35 Armament Subsystem as used on theAH-1G Cobrahelicopter. This variant fed from ammunition boxes fitted to the landing skid and was developed to provide the AH-1 helicopter with a longer-rangesuppressive fire system before the adoption of theM97 universal turret mounting theM197 cannon.[44]
The M61 is also the basis of the US NavyMk 15 Phalanxclose-in weapon system and theM163 VADS Vulcan Air Defense System, using the M168 variant.[45]
On 13 December 2024, theUkrainian Air Force claimed an F-16 shot down 6 Russian cruise missiles. Two were shot down with “medium-range missiles”, another two with “short-range missiles” and finally two with the M61 Vulcan 20 mm cannon. The pilot wasn't identified for security reasons but said: "A few bursts from the cannon — and an explosion... then another one! 'A secondary detonation,' I thought, but, as it turned out, there were two missiles,"[46]
Soviet Union/Russian Federation/CIS
... features new lightweight gun system is the General Dynamics M61A2, which has a switchable firing rate of 4,000 or 6,000 rounds per minute and a fully integrated linkless ammunition feed system
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