M68 (tank gun)

The M68 is an American 105 mm tank gun. It uses British-designed L7 gun tube and cartridges with an American-designed mount, breech assembly and recoil mechanism.

M68
Front view of a M68E1 gun on an American M60A3 main battle tank during a military exercise in Nuremberg, 1986.
TypeTank gun
Place of originUnited States
United Kingdom
Service history
In service1960–present
Production history
DesignerWatervliet Arsenal
ManufacturerWatervliet Arsenal
Produced1959–present
VariantsM68E1, M68A1, M68A1E4
Specifications
Mass754 kg (1,662 lb) (gun tube)
1,128 kg (2,487 lb) (recoiling gun mass)
Length5,550 mm (218.50 in) (overall)
Barrel length5,347 mm (210.51 in) (gun tube)
Shell105×617mm. R
Calibre105 mm (4.134 in)
Breechsemi-automatic vertical sliding-breechblock
Recoil305 mm

Technical characteristics

The M68 differs from the L7 in several aspects :

  • The M68 uses a concentric recoil spring instead of a separate buffer and recuperator hydraulic cylinders.
  • The M68 has a cylindrical breech with a vertical sliding breech block instead of a square-shaped breech with a horizontal sliding breech block.[1]
  • Firing is electrical only.
  • The M68 barrel is secured to the breech by a tapered pin and interrupted breech threads which allow the barrel to be removed from the gun shield without having to dismantle the mantlet.[2]
  • The M68 is fitted with an eccentric bore evacuator instead of a concentric model in order to provide more clearance over the rear deck.
  • The M68 chamber has a difference in the length of its shoulder, producing a different diametral taper near the freebore.

Models
  • M68 : initial production variant, used on the original variant of the M60 tank and the M116 gun mount.[3] Retrofitted to the M48A5.
  • M68E1 : variant used on the M60A1 and M60A3 tanks in mount M140. They were fitted with a fiberglass thermal shroud[4] in 1973.
  • M68A1 : improved variant built in 1980[5] for use on the M1 and IPM1 versions of the M1 Abrams.[6][7] The M68A1 features an aluminium thermal shroud and a pad for fixing the muzzle reference sensor.
  • M68A1E4 : a light weight, low-recoil version of the M68A1 designed for the M1128 Mobile Gun System (Stryker MGS). Also designated as M68A2, it features an Ares Incorporated long stroke, low recoil impulse mechanism and a muzzle brake (later removed).[8] The breech is mounted upside down to accommodate the automatic loader.

Foreign variants
  • KM68A1 : licence-produced variant of the US M68A1 gun for the South Korean Army. Used on the South Korean variant of the M48, the M48A5K and K1 tanks.
  • M68T : Turkish licence-built versions by MKEK under the designation of M68T to up-gun its 90 mm armed M48 fleet, took place in the 1980s.
  • M64 L71A : Israeli variant built by IMI for the Merkava Mk. I and Mk. 2 tanks.

Prototypes
  • T254E1 : US designation for the L7A1, it had the same horizontal sliding breech block as the L7 and used British X15/L52 barrels with a concentric bore evacuator on the barrel.
  • T254E2 : US variant of the T254, it had a vertical drop breech block with the X15E8 barrel and a concentric bore evacuator. Later standardized as M68. Used in M60 Patton prototype vehicles.
  • T254E3 : US variant designed in 1975, identical to thee T254E2/M68 but with chrome-plated bores. Only two built.[9][10]
  • XM24 : the XM24[11] gun tube was extended by 1.5 m (4 ft 11 in) compared to the M68A1 and it could tolerate a higher chamber pressure. Designed to replace the 105mm gun M68A1 in the M1 and the IPM1, it was expected to have improved penetration performance, particularly with the upcoming XM900 APFSDS (later cancelled and superseded by the M900A1). At that time, it was expected that the installation of the enhanced 105 mm gun would be less costly than retrofitting the M1 and IPM1 with the 120 mm gun M256. The program was initiated in March 1983, the Watervliet Arsenal manufactured 14 XM24 tubes and 17 breeches for cannon during the fiscal year 1984.[12] The US Army completed the advanced development phase in February 1984 and initiated it for the M1 in March. Full-scale development was expected to begin in November 1984 for the M60A3 and in January 1985 for the Abrams but the program was abandoned.[13]

Usage
  • M1 Abrams: M68A1 cannon used early production models (M1 and IPM1)
  • M47 Patton: in some upgraded variants
    • M47M: Iranian modification of US-supplied M47Ms
    • Sabalan: Iranian modification
    • Tiam: Iranian modification
  • M48 Patton: in some upgraded variants
    • M48A5: US model
    • Magach 3: Israeli modification
    • CM-11 Brave Tiger: Taiwanese modification
    • CM-12 Tank: Taiwanese modification
    • M48A5K1: South Korean modification
    • M48A5T1: Turkish modification
  • M60 tank: M60 and M60A1 using M68, M60A3 using M68E1[14]
  • M1128 Mobile Gun System: M68A1E4 cannon
  • Expeditionary Tank
  • K1 Type 88: KM68A1 cannon
  • Merkava: Mark I and Mark II models
  • T-54/55: in some upgraded variants
    • Tiran-4Sh: Israeli modification of T-54, both L7 and M68 variants fitted
    • Tiran-5Sh: Israeli modification of T-55, both L7 and M68 variants fitted
    • Type 72Z: Iranian modernization of T-54/55 and Type 59
    • Ramses II: Egyptian modernization of T-55

See also
  • CN105 F1 (French counterpart)
  • D-10T (Soviet counterpart)
  • U-5TS (Soviet 115 mm counterpart)

References
  1. Conners, Chris. "105mm Gun Tank M60". afvdb.50megs.com. Retrieved 19 August 2022.
  2. Foss, Christopher (1993). Jane's Armoured Fighting Vehicle Retrofit Systems 1993-94. London: Jane's Information Group. p. 41. ISBN 978-0710610799.
  3. Direct Support, General Support, and Depot Maintenance Manual for Cannon, 105-MM Gun, M68 & M68E1, M116 and 140.TM 9-1000-213-35 by Fred C. (Chief of Staff) Weyand Jan 1, 1978
  4. Hunnicutt, R.P. (2015). Patton: A History of the American Main Battle Tank. Echo Point Books & Media. p. 443. ISBN 978-1626548794.
  5. Cannon, 105mm Gun: M68A1E2 MIL-C-45504A Rev. D Jan 1987 Military and Government Specs & Standards (Naval Publications and Form Center) (NPFC)
  6. Hunnicutt, R.P. (1990). Abrams: A History of the American Main Battle Tank. Presidio. p. 312. ISBN 9780891413882.
  7. M1 Abrams in Action By Jim Mesko – 1996 Squadron/Signal publications
  8. "Army Programs - Stryker - Mobile Gun System (MGS)" (PDF). DOT&E. p. 83.
  9. Hunnicutt, R. P. Patton: A History of the American Main Battle Tank. 1984; Presidio Press. ISBN 0-89141-230-1 p.119
  10. "Data" (PDF). apps.dtic.mil. Archived (PDF) from the original on December 1, 2020. Retrieved 2020-04-11.
  11. "M60A3 Patton Tank Thermal Sight (TTS)". www.globalsecurity.org.
  12. "M60A3 Patton Tank Thermal Sight (TTS)". globalsecurity.org. Retrieved 19 August 2022.
  13. Hunnicutt, R.P. (1990). Abrams: A History of the American Main Battle Tank. Presidio. p. 202. ISBN 9780891413882.
  14. "M60 Patton Series - Globalsecurity.org". Archived from the original on 2008-12-02. Retrieved 2008-12-02.
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