M39 cannon

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M39
Cannon M39A2.png
M39 cannon in the nose of a Brazilian F-5.
TypeSingle-barrel Autocannon
Place of originUnited States
Service history
In service1952–present
Production history
DesignerFord Motor Company
Designed1951
ManufacturerPontiac, Ford, FMC Corporation, and others
No. built35,500+
VariantsM39, M39A1, M39A2, M39A3
Specifications
Weight80.9 kg (178.5 lb)
Length1.83 m

Caliber20 mm (0.787 in) × 102 mm
BarrelsSingle barrel (progressive RH parabolic twist, 9 grooves)
Actionfive-chamber revolver
Rate of fire1,500 rpm
Muzzle velocity1,030 m/s (3,300 ft/s)
The M-39 cannon with its 20 mm ammunition linkfeed.

The M39 cannon is a 20 mm caliber single-barreled revolver cannon developed for the United States Air Force in the late 1940s. It was used on a number of fighter aircraft from the early 1950s through the 1980s.

Development[edit]

The M39 was developed by the Springfield Armory, based on the World War II–era design of the German Mauser MG 213, a 20 mm (and 30 mm) cannon developed for the Luftwaffe, which did not see combat use. The same design inspired the 30mm British ADEN cannon and the French DEFA, but American designers chose a smaller 20 mm round to increase the weapon's rate of fire and muzzle velocity at the expense of hitting power. The 20×102mm round was later chosen by France for the M621 cannon.[1]

Initially designated the T-160, the new gun was installed for combat testing on a number of F-86 Sabre aircraft under the "GunVal" program in late 1952, and used in action over Korea in early 1953. It was subsequently adopted as standard armament of the F-86H fighter-bomber, F-100 Super Sabre, F-101A and F-101C Voodoo, and the F-5 Freedom Fighter. The M39 was also used on the B-57B tactical bomber. Current models of the F-5 Tiger II still use the M39A2 version of this weapon. The M39A2 was introduced in 1964.[2]

The weapon is gas operated and consists of a five–chamber magazine running parallel to the barrel. Sealing was provided by a forcing cone that was pressed into the barrel. Some 35,000 were produced before being superseded by the M61 cannon which outperformed the M39 in almost every way.[3] The only US aircraft still flying with the M39 is the Northrop F-5, an aircraft now only used for training. Extensive work had to be done on the forcing cone, heat dissipation, cook-off prevention, link testing, and reinforcement, to raise the mean time between failures to 1-in-1000 rounds fired.[4] Four arms manufacturers, three independent companies, and a university research department, were involved in getting the weapon working correctly.[5]

In Vietnam in 1967 the 116th Assault Helicopter Company operating out of Củ Chi Base Camp used the M39 mounted inverted on the forward hardpoints on the underside of a UH-1 helicopter, with ammunition feed out the left cargo door through a chute. The unit's report for May through July 1967 states "A low-level type of attack has been used on bunker lines with a good deal of success. It consists of locating and pinpointing the target area, then turning out, dropping down to about 50 feet (at 120 knots) and when about 500 meters from the target, popping up to about 150 feet, turning hell, death and destruction onto the target, turning off, and being gone before Charlie recovers from the shock....It is most effective on huts or heavily wooded tree lines. A hut is almost totally destroyed, i.e., to the point of setting it on fire and reducing it to ashes, and a tree line is so effectively covered that many of the trees are defoliated or limbs, etc., blown off. In situations where the enemy is using less than bunker-type cover, the 20mm coverage is so effective that it is quite reasonable to assume that those individuals who were in the area are either dead or severely wounded."[6] As to the ammunition, the same unit report says, "The ammunition is M-56AZ high explosive incendiary #12 link. It weighs almost one pound per round and has a bursting radius of 9 meters. It is spin-actuated at about 50 meters. It detonates upon contact with anything."

The M39 served as the basis for the T75 autocannon developed by the Republic of China (Taiwan), as a more-powerful partial replacement for the M2HB machine gun onboard naval vessels and the HMMWV tactical vehicle, with its latest use being within the XTR-101 and XTR-102 weapon stations.

Projectile specifications[edit]

  • Projectile weight: 101 g (3.56 oz)
  • Types
M56A3
HE-I with a 10.7-gram RDX explosive charge and a 1.3-gram incendiary charge[7]
M242
HE-I-T
M53
AP-I steel tip has a 50% chance of penetrating 6.3 mm of RHA at a range of 1,000 meters and striking angle of 0°.[8]
M775
AP-I-T
M55A2
TP
M220
TP-T

See also[edit]

References[edit]

  1. ^ Jane's Ammunition Handbook, Coulsdon: Jane's Information Group Ltd., 1993, p. 40.
  2. ^ Jane's Air Launched Weapons, Coulsdon: Jane's Information Group Ltd., 2000, p. 602.
  3. ^ http://ww2.rediscov.com/spring/VFPCGI.exe?IDCFile=/spring/DETAILS.IDC,SPECIFIC=14272,DATABASE=objects,
  4. ^ http://ww2.rediscov.com/spring/VFPCGI.exe?IDCFile=/spring/DETAILS.IDC,SPECIFIC=14272,DATABASE=objects,
  5. ^ http://ww2.rediscov.com/spring/VFPCGI.exe?IDCFile=/spring/DETAILS.IDC,SPECIFIC=14272,DATABASE=objects,
  6. ^ http://www.vhpa.org/unit/269CABMay-Jul1967Part1.pdf
  7. ^ "aircav.com - ammunition: 20mm". Retrieved 2011-07-11.
  8. ^ "aircav.com - ammunition: 20mm". Retrieved 2011-07-11.

External links[edit]