M39 cannon

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.

M39
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
Mass80.9 kg (178.5 lb)
Length1.83 m
Cartridge20×102 mm
Caliber20 mm (0.8 in)
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 chute

Development

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. The results of the program were startling, with the GUNVAL F-86F's having downed 6 MIG fighters and damaged 12 others. This signaled the end of the M3 .50 caliber as the preferred fighter weapon system ongoing.[2] 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.[3]

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 Some 35,000 were produced before being superseded by the M61 cannon which outperformed the M39 in almost every way.[4] The only US aircraft still flying with the M39 is the Northrop F-5, an aircraft now only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.[5] Four arms manufacturers, three independent companies, and a university research department, were involved in getting the weapon working correctly.[6]

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."[7] 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."

While a major leap forward in aircraft armament, all revolver cannon suffer from the effects of barrel wear, heat dissipation, and parts life. The final improved version of the M 39 had barrel changes mandated at 4000 rounds.[8]. The system would be replaced by the M61 Vulcan in aircraft for this and MTBF as well as weight considerations.[9]

T-75 cannon
ROCMC Humvee with T-75M 20mm Cannon
T-75S 20mm Cannon Mounted on FACG-77

The M39 served as the basis for the T-75 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.[10]

Projectile specifications
  • 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[11]
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°.[12]
M775
AP-I-T
M55A2
TP
M220
TP-T
gollark: I just want to know how to idiomatically make GCable wrappers for the various C objects.
gollark: No, I have that stuff done.
gollark: I want a *different* set of "OPERATIONS ON RELEVANT NODE THING" and no HTML generation at the end, and it would be bees to just copy-paste the function here.
gollark: As of now, my code does```nimproc renderToHtml*(input: string): string = let wlRegex = re"\[\[([^:\]]+):?([^\]]+)?\]\]" let opt = CMARK_OPT_UNSAFE or CMARK_OPT_FOOTNOTES or CMARK_OPT_STRIKETHROUGH_DOUBLE_TILDE or CMARK_OPT_TABLE_PREFER_STYLE_ATTRIBUTES # create parser instance let str: cstring = input len: csize_t = len(input).csize_t parser: ParserPtr = cmark_parser_new(opt.cint) if parser == nil: raise newException(CatchableError, "failed to initialize parser") defer: cmark_parser_free(parser) [further initialization stuff] # parse document, get AST cmark_parser_feed(parser, str, len) let doc = cmark_parser_finish(parser) defer: cmark_node_free(doc) if doc == nil: raise newException(CatchableError, "parsing failed - should not occur") # iterate over AST using built-in cmark-gfm AST iteration thing for (evType, node) in cmarkTree(doc): # if it is a text node [OPERATIONS ON RELEVANT NODE THING] let html: cstring = cmark_render_html(doc, opt.cint, cmark_parser_get_syntax_extensions(parser)) defer: free(html) result = $html```
gollark: cmark. I will explain.

See also

References
  1. Jane's Ammunition Handbook, Coulsdon: Jane's Information Group Ltd., 1993, p. 40.
  2. https://apps.dtic.mil/dtic/tr/fulltext/u2/a179871.pdf Pg 7
  3. Jane's Air Launched Weapons, Coulsdon: Jane's Information Group Ltd., 2000, p. 602.
  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://ww2.rediscov.com/spring/VFPCGI.exe?IDCFile=/spring/DETAILS.IDC,SPECIFIC=14272,DATABASE=objects,
  7. http://www.vhpa.org/unit/269CABMay-Jul1967Part1.pdf
  8. https://apps.dtic.mil/dtic/tr/fulltext/u2/a179871.pdf pg 14/15
  9. https://apps.dtic.mil/dtic/tr/fulltext/u2/a179871.pdf pg 14/17,
  10. "TADTE 2013". www.sadefensejournal.com. Small Arms Defense Journal. Retrieved 1 July 2019.
  11. http://ugcsurvival.com/FieldManuals/FM%201-140%2019960329-Helicopter%20Gunnery.pdf
  12. http://ugcsurvival.com/FieldManuals/FM%201-140%2019960329-Helicopter%20Gunnery.pdf
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