Designator:
M61A1, GAU 4 Vulcan
Name:
20-MM Vulcan CANNON
Type: Gatling-Type Cannon
Manufacturer: General ElectricDESCRIPTION:
The General Electric M61A1 Vulcan is a 6-barrel
20mm cannon used by a wide variety of American combat aircraft. The 6-barreled
GE M61A1 has
been the standard internal gun armament on most US combat aircraft for over
30 years. (The self-powered GAU 4 is virtually identical). It can fire
standard 20mmx168 ammunition at up to 7200 rounds per minute. In many
applications, the rate of fire is selectable between "Low" 4000rds/min and
"High" 6000rds/min. Gun recoil listed above is at the "High" rate of fire.
M61A1 and the F-106:
The F-106A surprised everyone by having good
maneuverability and showing potential as being an excellent dogfighter. There
were some thought to using the F-106 for top cover in Vietnam. Among
suggestions were to apply tactical camouflage, fit a clear-view canopy, and
add internal cannon armament. Although the F-106 never actually did serve in
Vietnam, the suggestion of the addition of a gun was taken seriously. The gun
was not intended for air-to-air combat against enemy fighters, but was primarily
intended to provide extra firepower for a better close-in kill potential against
enemy bombers, but it was thought that it might also be useful in attacking
bombers flying at low altitude.
In support of the cannon armament program Convair issued a proposal to
re-equip the F-106 with an internal cannon, an optical gun-sight, and a
clear-view cockpit canopy in a program known as Project Six Shooter in 1972.
The
internal 20-mm M61A1 rotary cannon with 650 rounds was fitted inside the rear
half of the weapons bay, replacing the Genie nuclear-tipped rocket. However, the
four AIM-4F/G Super Falcon missiles could still be carried.
The gun system was
installed as a package (pod) inside an enclosure mounted inside the
rear of the weapons bay between the rear missile launcher rails providing an aerodynamic shield for the portion of the gun
protruding below the missile bay and out into the air stream. Gun-equipped
F-106As could be distinguished by a bulged fairing underneath the fuselage which
provided clearance for the rotating barrels of the cannon. As part of the
program, a new "clear-topped" canopy was tested, which eliminated the metal
strip above the pilot's head, markedly improving the cockpit visibility.
The gun installation was first tested 10 February
1969 on F-106A 58-0795 and
subsequently on F-106A 59-0092. A prototype gun-sight was developed at Tyndall AFB. The
gun was installed only on those F-106s that had vertical tape instruments. When
firing, the Vulcan was limited to only 4500 rounds per minute, compared to the
6000 rpm available when installed on the F-4E, due to limitations in the
hydraulic pump which rotated the weapon.
This innovation was not
provided for the F-106B two-seater.
M61A1 Operation: The M61 operates on the Gatling principle. 6
20-mm barrels are mounted on a geared rotor that is driven by a 20-hp electric
motor. As the motor turns the rotor, the cam follower on the bolt of each
rotating barrel follows a fixed cam path in the gun housing, opening and closing
the bolt once per revolution. Firing only once per revolution reduces each
barrel's rate of fire to below that of most single-barrel revolver cannon. GE
claims that this continuous rotary motion eliminates the impact loads on gun
components and that sharing the thermal duty cycle among 6 barrels
"significantly" increases barrel life. The use of external power
eliminates jamming due to a misfired round.
In aircraft with the double-ended, hydraulically
driven link-less feed system, rounds stored along longitudinal rails within the
drum are moved to the gun end by a helix; the helix is made of Fiber-Reinforced
Plastic (FRP) in the F/A-18. A rotating scoop disc assembly transfers the rounds
to a rotating retaining ring. The rounds travel partway around the ring to the
exit unit, which puts the rounds into the chute that feeds the gun. Empty cases
are returned to the drum for storage.
STATUS:
Initial operational capability on F-105
Thunderchief in 1958. Built by General Electric Company, Burlington,
Vermont. In production and in service with all US armed force branches and
with several foreign air forces as well.
VARIANTS:
Phalanx CIWS:
Modified M61 for shipboard anti-missile use.
Built-in pulse-Doppler J-band fire control radar, and digital computer. See
separate entry.
Lightweight M61A1:
Lighter weight, has linear link-less feed
system, AIM-GUNS fire control software changes that expand the effective gun
envelope, and PGU-28/B Semi-Armor-Piercing High Explosive Incendiary
(SAPHEI) projectiles.
Sea Vulcan JM-61-MB:
M61 in open mount fitted on some Japanese
maritime safety patrol craft.
M35 Armament sub-system:
Mounted under the Bell AH-1G Huey Cobra's left
sponson, the M35 has the XM-195 gun, which is an M61A1 gun modified with
blast deflectors. The system weighs 1,168 lb (530 kg) loaded, 595 lb (270
kg) empty and carries about 950 rounds of ammunition which it fires at 4,500
shots/min.
300 M35 kits purchased beginning in 1968.
USERS/PLATFORMS
(The M61 gun is in widespread use by the United
States and many other nations on the following aircraft. Aircraft are listed
by the country of manufacture.)
CHARACTERISTICS:
| Weight |
SUU-16/A pod |
With 1,200 rounds:1,719 lb
(780 kg)
Empty:1,067 lb (484 kg) |
| SUU-23/A |
With 1,200 rounds:1,730 lb
(785 kg)
Empty:1,078 lb (489 kg) |
| GAU 4 |
275 lb (125 kg) |
| M61A1 gun |
Standard: 252 lb (114 kg)
Lightweight: 205 lb ( 93 kg) |
| Dimensions |
SUU-16/A, 23/A2 pods |
Length: 16 ft 7 in (5.05 m)
Diameter: 22 in (560 mm) |
| M61A1 |
Length: 6 ft 1.4 in (1.86 m)
Diameter: 1 ft 1.5 in (343 mm)
Recoil: 0.25 in (6.4 mm)
|
| Armament |
bore |
6 x 20-mm rifled barrels on a geared
rotor mounting
M61A1 is driven by external electrical or hydraulic power
GAU 4 is self-driven by gun exhaust gases |
| load/fire system |
bolt on each rotating barrel opens and
closes as it follows fixed cam path ammunition feed and storage
link-less feed from 1,020 to 1,200 round storage drum |
| Performance |
rate of fire |
typical:
6,000 rpm
maximum: 7,200 rpm |
| average recoil force |
4,000 shots/min:
2,661 lb (1,207 kg)
6,000 shots/min: 3,818 lb (1,732 kg) |
| muzzle velocity |
M56 projectile:
3,380 fps (1,030 mps)
PGU-28/B: 3,450 fps (1,052 mps) |
| USA |
A-7 Corsair
F-4 Phantom
F-14 Tomcat
F-15 Eagle
F-16 Fighting Falcon
F-18 Hornet
F-106 Delta Dart
F-111
AH-1G Cobra |
| Brazil/Italy |
AMX |
| Italy |
Aeritalia F-104S Starfighter |
| Japan |
F-1
T-2 |
|
Many other
aircraft can accept the M61 in the SUU-16 or SUU-23 externally mounted
pods. |
As part of the Phalanx Close-in Weapon System (CIWS), it is in service
on most US Navy ships and many ships of foreign navies. |
|
