M68 tank gun

{{Infobox weapon |name=M68 |image=File:NATO exercises in Nurenberg, Germany January 1986 (1) - photo by Nancy Wong.jpg |image_size=300 |caption=Front view of a M68E1 gun on an American M60A3 main battle tank during a military exercise in Nuremberg, 1986. |origin= United States<br>United Kingdom |type=Tank gun  |is_ranged=yes |is_bladed= |is_explosive= |is_artillery=no |is_vehicle= |is_UK=no  |service=1960–present |used_by= |wars=  |designer= Watervliet Arsenal |design_date= |manufacturer= Watervliet Arsenal |production_date=1959–present |number= |variants= M68E1, M68A1, M68A1E4  |weight={{convert|754|kg|lb|abbr=on}} (gun tube)<br>{{convert|1128|kg|lb|abbr=on}} (recoiling gun mass) |length={{convert|5550|mm|abbr=on|2}} (overall) |part_length={{convert|5347|mm|abbr=on|2}} (gun tube) |width= |height= |crew=  |cartridge=105×617mm. R |caliber={{convert|105|mm|abbr=on|3}} |action= |rate= |velocity= |range= |max_range= |feed= |sights=  |breech=semi-automatic vertical sliding-breechblock |recoil=305 mm |carriage= |elevation= |traverse= |}}

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

== 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.<ref>{{cite web |last1=Conners |first1=Chris |title=105mm Gun Tank M60 |url=http://afvdb.50megs.com/usa/m60.html |website=afvdb.50megs.com |access-date=19 August 2022}}</ref> *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.<ref>{{cite book |last1=Foss|first1=Christopher |title= Jane's Armoured Fighting Vehicle Retrofit Systems 1993-94 |date=1993 |publisher=Jane's Information Group |location=London |isbn=978-0710610799 |pages=41 }}</ref> *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.

== History == The main gun for the M60 tank series was chosen after a comparative firing test of six different guns carried out on the Aberdeen Proving Ground in 1958. The factors evaluated were accuracy, the lethality of a hit, rate of fire, and penetration performance.{{sfn|Hunnicutt|1984|pages= 151-152 }} Based on these tests, the 105 mm '''T254E1''' was selected, modified to the '''T254E2''' and standardized as the '''Cannon, 105-MM Gun, M68'''. The T254E2/M68 used a vertical sliding breechblock instead of the T254E1's horizontal breechblock. Until American-made barrels could be obtained with comparable accuracy, British X15/L52 barrels mounting a concentric bore evacuator on the barrel were to be used.{{sfn|Hunnicutt|1984|page= 155 }} US-built XM24/L52 barrels (length 218.5 inches)<ref>{{cite web |url=http://www.williammaloney.com/Aviation/WatervlietArsenalMuseum/TankCannon/pages/09M68_105mmGun.htm |title=09 M68 105mm Gun |website=www.williammaloney.com|access-date=2019-05-31|archive-url=https://web.archive.org/web/20180121075334/http://www.williammaloney.com/Aviation/WatervlietArsenalMuseum/TankCannon/pages/09M68_105mmGun.htm|archive-date=2018-01-21|url-status=live}}</ref> fitted with an eccentric bore evacuator were used for the M60-series starting in June 1959 but retained interchangeability with the British X15/L52 barrel.{{sfn|Hunnicutt|1984|page= 152 }} All of the US guns and XM24 barrels were produced at the Watervliet Arsenal in New York and the gun mounts (M116 for the M60 and M140 for the M60A1/A3) manufactured at the Rock Island Arsenal in Illinois.<ref>{{cite web |url= https://www.gao.gov/assets/190/188401.pdf|title=Procurement report |date=1976 |website= www.gao.gov|access-date=2020-04-11}}</ref> US M68 guns were fitted with an eccentric bore evacuator instead of a concentric model in order to provide more clearance over the rear deck of the tank.<ref name="Organizational Maintenance Manual--Tank 2306">TM 9-2350-253-20-2 Organizational Maintenance Manual--Tank, Combat, Full Tracked: 105-mm Gun, M60A3 (2350-00-148-6548) and (2350-01-061-2306) TTS Turret. Washington, D.C.: Dept. of the Army, 15 April 1980</ref> The original variant of the M60 tank was equipped with the M68 gun using the M116 mount.<ref>Direct Support, General Support, and Depot Maintenance Manual for Cannon, 105-MM Gun, M68 & M68E1, M116 and 140 mount TM 9-1000-213-35 by Fred C. (Chief of Staff) Weyand | Jan 1, 1978</ref> Additionally, many M48A3s armed with a 90mm gun that were in NG-CONUS service with the Army National Guard were retrofitted with the M68 gun and re-designated as the M48A5.<ref>{{Cite book |title=Abrams: A History of the American Main Battle Tank |last=Hunnicutt |first=R.P. |publisher=Presidio |year=1990 |isbn=9780891413882 |pages=209–210}}</ref> This was done to maintain training levels of Guard units as well as using a commonality in ammunition amongst tanks.

The M60A1 and A3 variants of the M60 series<ref name="ReferenceA">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</ref> and earliest pre-production XM1 prototypes of the M1 Abrams tanks<ref>M1 Abrams in Action By Jim Mesko – 1996 Squadron/Signal publications p.27</ref> are armed with the '''M68E1''' variant of the gun. The M68E1 gun shares the same firing characteristics as the M68. It featured several design improvements including an updated gun hydraulic configuration, a stabilization upgrade for the gun, a gun elevation kill switch for the loader, improved ballistic drive and other component refinements.<ref name="ReferenceA"/> They were fitted with thermal sleeves on the barrels starting in 1973.<ref name="auto1">{{cite web|url=https://archive.org/details/DTIC_ADA090007|title=DTIC ADA090007: Comparison of Mechanical Properties of 105mm M68 Gun Tube Forgings|date=May 1, 1980|via=Internet Archive}}</ref> During the mid 1970s it was becoming clear that the latest generation of composite based armor was impervious to tungsten carbide penetrators.<ref name="auto4">{{cite web|url=https://www.pica.army.mil/Picatinny/products_services/products12.aspx?AspxAutoDetectCookieSupport=1 |archive-url=https://web.archive.org/web/20210913154831/https://www.pica.army.mil/Picatinny/products_services/products12.aspx?AspxAutoDetectCookieSupport=1 |url-status=dead |archive-date=September 13, 2021 |title=Picatinny Arsenal - The Joint Center of Excellence for Guns and Ammunition |publisher=Pica.army.mil |access-date=2020-04-11}}</ref><ref name="auto3">{{Cite web|url=https://www.globalsecurity.org/military/systems/munitions/m774.htm|title=M774 105mm, APFSDS-T|website=www.globalsecurity.org}}</ref> Work was performed at the Department of Energy's Pacific Northwest National Laboratory to engineer development of depleted uranium as a penetrator material for future ammunition while the Armament Research and Development Command (ARRADCOM) was improving the performance of the 105mm M774 cartridge.<ref name="auto3"/><ref name="auto4"/> The improved M833 round starting in 1983, also using a depleted uranium penetrator to keep the M68E1 gun viable against this improved armor. In 1975 an updated version of the gun, the '''T254E3''' was designed, focusing on the use of chrome plating to improve accuracy. It was used to evaluate improvements to the gun's performance using discarding sabot ammunition. Two guns were built and underwent firing trials at Aberdeen<ref>^Aberdeen Proving Ground Report No. FR-P-82476, 22 April 1975</ref> and technical evaluations at the Watervliet Arsenal.<ref>Watervliet Arsenal Report No. WVT-TR-75047, Analysis of Wear Data from 105mm M68 Gun Tubes in Field Service, July 1975</ref> Based on the results of these tests the shortcomings of plated bores and gun tubes were found to outweigh any advantage they might offer and the program dropped by May 1976.<ref>USA TECOM Report No. APG-MT-4802, Product Improvement Test of Gun, 105mm M68 TWear Resistant Plating Accuracy Phase, APG, May 1976</ref>

thumb|right|The interior of an XM1 Abrams, showing the breech end of the gun. In January 1978, a program was initiated<ref name="auto7">{{cite web|url=https://archive.org/details/DTIC_ADA051050|title=DTIC ADA051050: Initial Firing Test Results of the 35mm Scaled Model of the 105mm M68 Tank Gun|date=January 1, 1978|via=Internet Archive}}</ref> to develop an enhanced version of the 105mm gun, the '''M68A1''' as a possible alternate weapon for the M1 Abrams.<ref name="auto6">CANNON, 105MM GUN: M68A1E2 MIL-C-45504A Rev. D Jan 1987 | Military and Government Specs & Standards (Naval Publications and Form Center) (NPFC)</ref> had a higher chamber pressure,<ref>Hunnicutt, R.P. (1990). Abrams: A History of the American Main Battle Tank. Presidio. p. 312. {{ISBN|9780891413882}}. 105mm Gun Tank M1 and IPM1 in a combination mount (M68A1 Gun)</ref> reinforced breech<ref name="auto6"/> allowing the use of high-energy propellants.<ref name="auto7"/><ref>Direct Support, General Support, and Depot Maintenance Manual for Cannon, 105-MM Gun, M68 & M68E1, M116 and 140 Mount TM 9-1000-213-35 by Fred C. (Chief of Staff) Weyand | Jan 1, 1978</ref> Although the M256 120mm smoothbore gun was chosen to be the main weapon of the M1 Abrams in 1979, the ammunition for the gun was still not fully developed, thus delaying its fielding until 1984.<ref name="auto4"/> The early production versions of the M1 Abrams (M1 & IPM1) were armed with the M68A1<ref>Hunnicutt, R.P. (1990). Abrams: A History of the American Main Battle Tank. Presidio. p. 312. {{ISBN|9780891413882}}. 105mm Gun Tank M1 and IPM1 in a combination mount with M68A1 Gun</ref> for two reasons. First was due to the large number of M60 Patton tanks with the M68E1 gun still in widespread US service in the 1980s and a large on-hand stockpile of 105mm munitions. Fitting the M1 with the M68A1 gun was viewed as an economical and practical solution that allowed for commonality in ammunition among the two types of tanks.<ref>Osprey Publishing, New Vanguard #2: M1 Abrams Main Battle Tank 1982-1992, Steve Zaloga & Peter Sarson</ref> Secondly was that the M68A1E2 could employ the newly developed M900A1 APFSDS<ref name="auto2">{{Cite web|url=https://www.globalsecurity.org/military/systems/munitions/m900.htm|title=M900 105mm APFSDS-T|website=www.globalsecurity.org}}</ref> depleted uranium round that had improved penetration performance in comparison to the M833.<ref>{{cite web|url=https://www.pica.army.mil/Picatinny/(X(1)S(jnp3njocqw3j4rrsh5iyrqn2))/products_services/products12.aspx?AspxAutoDetectCookieSupport=1 |archive-url=https://web.archive.org/web/20200618163520/https://www.pica.army.mil/Picatinny/(X(1)S(jnp3njocqw3j4rrsh5iyrqn2))/products_services/products12.aspx?AspxAutoDetectCookieSupport=1 |url-status=dead |archive-date=June 18, 2020 |title=Picatinny Arsenal - The Joint Center of Excellence for Guns and Ammunition |publisher=Pica.army.mil |access-date=2020-04-11}}</ref> These early versions of the M1 Abrams were in active Army service until 1991 and with National Guard units until 1996.<ref>M1 Abrams in Action By Jim Mesko – 1996 Squadron/Signal publications p. 72</ref> M1s built after 1984 were armed with the 120mm M256 and designated the M1A1. Many earlier M1 and IPM1 tanks were refitted with the M256 and their designations changed to the M1A1.

The M1128 Stryker mobile gun system (MGS) carries the '''M68A1E4''' 105 mm cannon. The principal function of the MGS is to provide rapid direct fire to support assaulting infantry.<ref>{{cite web |title=The Stryker Mobile Gun System: A Case Study on Managing Complexity |url= https://apps.dtic.mil/dtic/tr/fulltext/u2/a501145.pdf |publisher=apps.dtic.mil |access-date=26 January 2023 |archive-url= https://web.archive.org/web/20191214133533/https://apps.dtic.mil/dtic/tr/fulltext/u2/a501145.pdf |url-status=live |archive-date=December 14, 2019}}</ref> The cannon is mounted in a low-profile, fully stabilized turret integrated into the Stryker chassis.<ref>{{Cite web|url=https://www.globalsecurity.org/military/systems/ground/iav-mgs.htm|title=M1128 Stryker Mobile Gun System|website=www.globalsecurity.org}}</ref> The M68A1E4 is based on the M68A1E2 105mm cannon's design. It has a sustained fire rate of six rounds per minute. The gun employs four types of cartridges. The M900A1 kinetic energy penetrator to destroy armored vehicles; the M456A2 high explosive anti-tank round to destroy thin-skinned vehicles and provide anti-personnel fragmentation; the M393A3 high explosive plastic round to destroy bunkers, machine gun and sniper positions, and breach openings in walls for infantry to access; and M1040 canister shot for use against dismounted infantry in the open.<ref>{{cite web |last=Hill |first=Paul |title=NDIA Joint Armaments Conference |url=http://www.dtic.mil/ndia/2013armament/Hill.pdf|archive-url=https://web.archive.org/web/20140826115937/http://www.dtic.mil/ndia/2013armament/Hill.pdf |archive-date=2014-08-26|url-status=dead|date=August 26, 2014}}</ref>

== Models == thumb|right|A U.S. Army M1128 mobile gun system fires its M68A2 tank gun in 2011 *'''M68''' : initial production variant, used on the original variant of the M60 tank and the M116 gun mount.<ref>''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</ref> Retrofitted to the M48A5. *'''M68E1''' : variant used on the M60A1 and M60A3 tanks in mount M140. They were fitted with a fiberglass thermal shroud<ref name=":0">{{Cite book|title=Patton: A History of the American Main Battle Tank|last=Hunnicutt|first=R.P.|publisher=Echo Point Books & Media|year=2015|isbn=978-1626548794|page=443}}</ref> in 1973. *'''M68A1''' : improved variant built in 1980<ref>Cannon, 105mm Gun: M68A1E2 MIL-C-45504A Rev. D Jan 1987 Military and Government Specs & Standards (Naval Publications and Form Center) (NPFC)</ref> for use on the M1 and IPM1 versions of the M1 Abrams.<ref name=":1">{{Cite book|title=Abrams: A History of the American Main Battle Tank|last=Hunnicutt|first=R.P.|publisher=Presidio|year=1990|isbn=9780891413882|page=312|quote= }}</ref><ref>''M1 Abrams in Action'' By Jim Mesko – 1996 Squadron/Signal publications</ref> The M68A1 features an aluminium thermal shroud and a pad for fixing the muzzle reference sensor. *'''M68A1E4''' : a lightweight, low-recoil version of the M68A1 designed for the M1128 mobile gun system (Stryker MGS). Also designated as '''M68A2''',{{citation needed|date=February 2023}} it features an Ares Incorporated long stroke, low recoil impulse mechanism and a muzzle brake (later removed).<ref>{{cite web|url=https://www.dote.osd.mil/pub/reports/FY2005/pdf/army/2005strykermgs.pdf|title=Army Programs - Stryker - Mobile Gun System (MGS)|website=DOT&E|page=83}}</ref> 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 prototype vehicles. *'''T254E3''' : US variant designed in 1975, identical to thee T254E2/M68 but with chrome-plated bores. Only two built.<ref>{{cite book |last=Hunnicutt |first=R. P. |title=Patton: A History of the American Main Battle Tank |date=1984 |publisher=Presidio Press |isbn=0-89141-230-1 |page=119}}</ref><ref>{{cite web|url=https://apps.dtic.mil/dtic/tr/fulltext/u2/a031639.pdf |archive-url=https://web.archive.org/web/20201201160950/https://apps.dtic.mil/dtic/tr/fulltext/u2/a031639.pdf |url-status=live |archive-date=December 1, 2020 |title=Data |publisher=apps.dtic.mil |access-date=2020-04-11}}</ref> *'''XM24''' : the XM24<ref>{{cite web|url=https://www.globalsecurity.org/military/systems/ground/m60a3.htm|title=M60A3 Patton Tank Thermal Sight (TTS)|website=www.globalsecurity.org}}</ref> gun tube was extended by {{convert|1.5|m|ftin|abbr=on|sigfig=1}} 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.<ref>{{cite web |title=M60A3 Patton Tank Thermal Sight (TTS) |url=https://www.globalsecurity.org/military/systems/ground/m60a3.htm |website=globalsecurity.org |access-date=19 August 2022}}</ref> 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.<ref>{{Cite book |title=Abrams: A History of the American Main Battle Tank |last=Hunnicutt |first=R.P. |publisher=Presidio |year=1990 |isbn=9780891413882 |pages=202}}</ref>

== 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 **CM11 Brave Tiger: Taiwanese modification **CM12 tank: Taiwanese modification **M48A5K1: South Korean modification **M48A5T1: Turkish modification *M60 tank: M60 and M60A1 using M68, M60A3 using M68E1<ref>{{cite web |url=http://www.globalsecurity.org/military/systems/ground/m60.htm |title=M60 Patton Series - Globalsecurity.org |access-date=2008-12-02 |archive-url=https://web.archive.org/web/20081202021849/http://www.globalsecurity.org/military/systems/ground/m60.htm |archive-date=2008-12-02 |url-status=live }}</ref> * 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) *M35 tank gun, an American lighter variant of the M68 with a shorter recoil<ref name=forecast>{{cite web |title=M8 Armored Gun System - Archived 3/2004 |url=https://www.forecastinternational.com/archive/disp_pdf.cfm?DACH_RECNO=433 |website=www.forecastinternational.com |publisher=Forecast International |access-date=28 March 2019 |archive-date=March 28, 2019 |archive-url=https://web.archive.org/web/20190328042857/https://www.forecastinternational.com/archive/disp_pdf.cfm?DACH_RECNO=433 |url-status=live}}</ref>

==References== {{Reflist}}

Category:Tank guns of the United States