M60 tank

Information was found on Wikipedia.

# [UNFINSHED]

The **M60** is an American second-generation main battle tank (MBT). It was officially standardized as the **Tank, Combat, Full Tracked: 105-mm Gun, M60** in March 1959. Although developed from the M48 Patton, the M60 tank series was never officially christened as a Patton tank. The US Army considered it a "product-improved descendant" of the Patton tank's design. The design similarities are evident comparing the original version of the M60 and the M48A2. It has been sometimes informally grouped as a member of the Patton tank family. The United States fully committed to the MBT doctrine in 1963, when the Marine Corps retired the last (M103) heavy tank battalion. The M60 tank series became America's primary main battle tank during the Cold War. Over 15,000 M60s were built by Chrysler. Hull production ended in 1983, but 5,400 older models were converted to the M60A3 variant ending in 1990.

The M60 reached operational capability upon fielding to US Army European units beginning in December 1960. The first combat use of the M60 was by Israel during the 1973 Yom Kippur War, where it saw service under the "Magach 6" designation, performing well in combat against comparable tanks such as the T-62. In 1982 the Israelis again used the M60 during the 1982 Lebanon War, equipped with upgrades such as explosive reactive armor to defend against guided missiles that proved very effective at destroying tanks. The M60 also saw use in 1983 during Operation Urgent Fury, supporting US Marines in an amphibious assault on Grenada. M60s delivered to Iran also served in the Iran–Iraq War.

The United States' largest deployment of M60s was in the 1991 Gulf War, where the US Marines equipped with M60A1s effectively defeated Iraqi armored forces, including T-72 tanks. The United States retired the M60 from front-line combat after Operation Desert Storm, with the last tanks being retired from National Guard service in 1997. M60-series vehicles continue in front-line service with a number of countries' militaries, though most of these have been highly modified and had their firepower, mobility and protection upgraded to increase their combat effectiveness on the modern battlefield.

The M60 underwent many updates over its service life. The interior layout, based on the design of the M48, provided ample room for updates and improvements, extending the vehicle's service life for over four decades. It was widely used by the US and its Cold War allies, especially those in NATO, and remains in service throughout the world, despite having been superseded by the M1 Abrams in the US military. The tank's hull was the basis for a wide variety of prototype, utility and support vehicles such as armored recovery vehicles, bridge layers and combat engineering vehicles. As of 2015, Egypt is the largest operator with 1,716 upgraded M60A3s, Turkey is second with 866 upgraded units in service, and Saudi Arabia is third with over 650 units.

## Development

### Impetus

The United States entered a period of frenzied activity during the crisis atmosphere of the Korean War, when America seemed to lag behind the Soviet Union in terms of tank quality and quantity. Testing and development cycles occurred simultaneously with production to ensure speedy delivery of new tanks. Such rapid production caused problems but the importance given to rapidly equipping combat units with new tanks precluded detailed testing and evaluation prior to quantity production.

The M47 Patton entered production in 1951 and was used by the United States Army and Marine Corps but ongoing technical and production problems kept it from serving in the Korean War. The M48 Patton tank entered US service in 1952 but its early designs were deemed unsatisfactory by Army Field Forces (AFF). The improvements to the M48 focused on improving the 90mm main gun and fire control systems while simultaneously exploring the development of silicas glass composite armor and autoloader systems. The tank continued further development through 1955 in conjunction with its simultaneous mass production. The course of its development during the mid 1950s was the source of widespread debate among Congressional Budget Oversight committees.

The T95 program, which began in 1955 was intended to supersede the M48. It featured a host of innovative and experimental components such as its 90 mm smoothbore T208 cannon rigidly affixed to its turret, experimental X-shaped engine design using a vapour-cycle power plant fueled by hydrocarbons, composite armor and infrared rangefinder. The burden of developing them, however, slowed the overall program to a crawl. During the Hungarian Revolution of 1956, a Soviet T-54A medium tank was driven onto the grounds of the UK's embassy in Budapest by the Hungarians in November.

After a brief examination of this tank's armor by a British military attaché it was concluded that the 20-pounder (84mm L/66.7) was apparently incapable of consistently defeating its frontal armor with High-Explosive Anti-Tank (HEAT) or Armor-Piercing Capped (APC) ammunition. Its 100 mm gun was a significant advancement over the weapon of the T-44.

There were also rumors of an even larger 115 mm gun in the works. These events spurred the United Kingdom to begin upgrading existing tanks with a 105mm high-velocity rifled gun in 1958, the Royal Ordnance L7 to keep the Centurion viable against this new Soviet tank design. The United States responded by starting development of the XM60 tank in September 1957. This new tank design incorporated many Army Combat Vehicle (ARCOVE) committee improvements to the M48A2, chiefly the use of diesel engines to increase its operational range and the use of a more powerful main gun.

### Choice of components

#### M68 105 mm main gun

The main gun 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, lethality of a hit, rate of fire and penetration performance.

An M48A2C was fit with the 90 mm M41 and tested with the new T300E53 HEAT round. A smoothbore version of the 90 mm, the T208E9, was mounted on the T95E1 tank and tested the T320E62 Armour-Piercing Discarding Sabot (APDS) round. An American variant of the British Royal Ordnance L7 tank gun, under the US designation 105 mm T254E1, was mounted on the T95E2 and tested with British APDS ammunition. Finally, two versions of the 120 mm gun from the M103 were trialed, the existing M58 model and a lightened variant known as T123E6 which was mounted on the T95E4.

The T123E6 was preferred by the Ordnance Department because its ammunition, the same as that for the M58 gun, was already at an advanced state of development. However the ammunition was in two parts, shell and propellant bag, which required significant time to load. In the M103 this was addressed by adding a second loader, but a medium tank would not have the internal space needed for another crewmember and the firing rate would suffer as a result. In testing it demonstrated a maximum rate of 4 rounds per minute vs. the T254's 7 rpm.

Based on these tests, the 105 mm T254E1 was selected, modified to the T254E2 and standardized as the "Cannon, 105mm Gun, M68". It used a vertical drop breechblock instead of the T254E1's horizontal sliding breechblock. Until American-made barrels could be obtained with comparable accuracy, British X15/L52 barrels were to be used. US built XM24/L52 barrels (length 218.5 inches) 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.

All of the US guns and XM24 barrels were produced at the Watervliet Arsenal, NY and the gun mounts (M116 for the M60 and M140 for the M60A1/A3) were manufactured at the Rock Island Arsenal, IL. Because the evacuator was positioned lower on the gun's barrel 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.

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 allowing the accurate firing of long dart penetrators and other component refinements.

The gun is capable of using a wide range of ammunition including APDS-Tracer (APDS-T) (M392 and M728), Armour-Piercing Fin-Stabilized Discarding Sabot-Tracer (APFSDS-T) (M735 and M774), APFSDS Depleted Uranium (DU) (APFSDS-DU) (M833), HEAT-FS (M456), APDS dummy and target practice rounds, High Explosive Plastic (HEP)/ High-Explosive Squash Head (HESH) (M393), white phosphorus and canister rounds. Barrels with thermal sleeves were used starting in 1973.

Both the original M60 variant as well and the initial configuration of the M60A1 used the M68 gun. Additionally, many M48A3s armed with a 90mm gun that were in service with the Army National Guard (ARNG) were retrofitted with the M68 gun during the mid 1970s and redesignated as the M48A5. This was done to maintain training levels of ARNG units as well as using a commonality in ammunition amongst tanks.

M60A1 RISE Passive tanks built after 1977 and all M60A3 tanks were armed with the M68E1 variant of the gun. It had an improved ballistic drive to allow for accurate firing of the M735 APFSDS ammunition. Most M60A1 RISE tanks were retrofitted to the this standard by applying the M735 Cam update from the M60A1 PIP Turret Update Kit. The earliest pre-production XM1 prototypes of the M1 Abrams tanks are also armed with the M68E1 variant of the gun.

#### Armor

Composite applique armor panels made with fused silica glass was intended to be fitted to the hull. This led to a redesign of the front of the hull into the shape of a flat wedge, instead of the M48's elliptical front, as it simplified the installation of this armor. It was also envisioned that the T95E6 turret was to be constructed solely with this special armor. The US Army Ordnance Tank Automotive Command (OTAC) and the Carnegie Institute of Technology began development of the armor in November 1952 at Fort Belvoir VA as Project TT2-782/51 using examples of the T95 tank to conduct the ballistics testing.

This composite armor provides protection against HEAT, HEP/HESH and HE rounds. However, field repaired panel castings suffered a loss of kinetic energy protection. Limitations in manufacturing capacity and the added cost led to this armor being dropped by November 1958 and all M60-series tanks were protected with conventional steel armor but the tank retained the capability to employ armor panels.

The M60-series was the last US main battle tank to utilize homogeneous steel armor for protection. It was also the last to feature an escape hatch under the hull. The escape hatch was provided for the driver, whose top-side hatch could easily be blocked by the main gun.

There were two versions of hulls used for the M60-series. The M60 hull had a straight slope and beak compared to the earlier M48's rounded one. The hull bottom had a strong boat-like appearance with a pronounced recess between the upper tracks and external suspension arms and one shock absorber on the first roadwheel pair. The armor was improved, at 6 inches (155 mm) on the front glacis and mantle of solid rolled homogeneous armor, while it was 4.3 inches (110 mm) on the M48. The first prototype hulls did not have shock absorbers and were briefly named M68 in late 1958 before the Ordnance Department renamed it the M60 in March 1959. This hull version was used only on the original M60 variant and early M728 Combat Engineer Vehicles (CEVs) and M60 Armored Vehicle Launched Bridges (AVLBs). This hull model was in production from 1959 to 1962.

The M60A1 hull has basically the same visual characteristics, the noticeable difference was the addition of a second shock absorber at the second roadwheel pair and was also accompanied by a slight relocation of the first return roller. These modifications were needed due to the increased weight of the M60A1 turret as well as the additional hull armor. This hull model was used on the M60A1, M60A2 and M60A3 models of the M60-series as well as the M728A1 CEV and M60A1 AVLB. It was in production from 1962 to 1983.

The M60-series went through a progressive turret design scheme during its production life with four different turrets being manufactured for the M60-series. The T95E5 turret used on the M60 was hemispherically shaped and bore a strong resemblance to the M48 Patton. The M60A1 was the first version to employ the newly designed T95E7 turret with a redesigned bustle increasing the number of rounds for the main gun to 63. The M60A2 featured a specially designed turret for the M162 gun/missile launcher that greatly reduced the frontal arc in comparison to the M60A1's T95E7 turret. The M60A3's turret was similar to the A1's but with increased armor protection for the frontal arc and mantlet in an effort to provide additional protection of the turret's hydraulics system.

#### M19 commander's cupola

A redesigned full vision cupola was envisioned for the commander's station. It had 7 tiltable vision blocks arranged to give the commander a 360 degree field of view with overlapping vision between adjacent vision blocks. The front vision block could be replaced with a dual power M34 7×50 binocular day sight or an M19E1 Infrared (IR) periscope. A special feature was that the cupola body could be raised up to 3+1⁄2 inches (9 cm) providing the commander a direct field of vision while remaining under armor protection.

Access was through a hatch cover on the roof and a .50 caliber M2 Heavy Barrel (HB) machine gun was pedestal mounted on the forward part of the cupola. It could be aimed and fired with the cupola closed. Also there was an 11 inch long hydraulically operated port on the left side allowing spent cartridge cases to be ejected.

After creating a full-sized mock up of this design using the T95E6 turret, it was dropped in favor of a design based on the M1 cupola of the M48A2's turret. This T9 cupola provided the commander with more headroom than the T6 cupola of the T95 tank, carrying a new short receiver M85/T175 .50 caliber machine gun and it was standardized as the Cupola, Tank Commander's Caliber .50 Machine Gun, M19. The first M19 cupola (a modified T9) was ready on 27 October 1958. It has an M28C sight for the machine gun in the forward part of the cupola and eight vision blocks. The front vision block can be replaced by a M19E1 infrared periscope or an M36E1 passive periscope for night observation.

Initial production of the cupola was problematic. The first 300 M60s produced were armed with a .50cal M2HB machine gun in a pedestal mount welded to the left side of the commander's cupola owing to production problems with the new M85 machine gun. Of these tanks, the first 45 manufactured were made without the cupola itself, also due to production problems. All of these early M60s eventually had the M19 cupola and M85 machine gun installed.

Compared to a conventional pintle mount, the remote-controlled M85 machine gun was relatively ineffective in the anti-aircraft role for which it was designed. Removing the cupola lowered the vehicle's relatively high silhouette. The cupola's hatch also opened toward the rear of the vehicle and was dangerous to close if under small-arms fire owing to a lock-open mechanism that required the user to apply leverage to unlock it prior to closing. The commander was able to observe the battlefield using the x4 binocular M34D daylight vision block or the M19E1 IR or M36 Passive periscopes while remaining under armor protection with a 360 degree traverse independent of the turret, was stabilized in azimuth and elevation and carried 600 rounds of ammunition.

All M60s in US service retained the M19 cupola until the tank was phased out of service. The few M60A3s in Army service as training vehicles had their commander's cupola removed as it was deemed unnecessary for training and to better mimic the profile of Soviet tanks. Some M48A5s were retrofitted with the M19 cupola to maintain training levels of ARNG units.

#### Main battle tank designation

The concept of the medium tank gradually evolved into the main battle tank (MBT) in the 1960s. The MBT was to combine the firepower and protection sufficient for the assault role with the mobility to perform as a medium tank. The MBT thus took on the role the British had once called the "universal tank" in the late 1950s, exemplified by the British Centurion, filling almost all battlefield roles. Typical MBTs were as well armed as any other vehicle on the battlefield, highly mobile, and well armored. Yet they were cheap enough to be built in large numbers.

The first generation consists of the medium tanks designed and produced directly after World War II that were later redefined as main battle tanks. These were exemplified by the M47 and M48 Pattons armed with a 90mm main gun already in widespread US service. The original variant of the M60 series also fulfilled the definition of a late first generation MBT sometimes being referred to as an intermediate second generation design. The Soviet T-54 and T-55 as well as the original configuration of the T-62A tank designs are also regarded as first generation MBTs.

The second generation had enhanced night-fighting capabilities and in most cases nuclear, biological and chemical (NBC) protection. Most western tanks of this generation were armed with the 105 mm Royal Ordnance L7 tank gun or derivatives of it. Notable are the British Chieftain and German Leopard 1. The United States fully committed to the MBT doctrine in 1963 when the Marine Corps deactivated its last M103 heavy tank battalion.

The first American nomenclature-designated second generation MBT was the M60A1 version of the M60 series. The term MBT is used in strategic doctrine and the composition of force as determined by the United States Army. The M60 series tanks fulfilled the MBT role on a strategic and tactical level. It was never referred to as such in any official training or technical manuals. The first Soviet second generation main battle tank designs were the T-64 and T-72.

### XM60 development

By May 1957 it became clear that the T95 Medium Tank would not have a significant advantage over the M48A2. The X-shaped motor and electro-optical rangefinder were both discarded due to performance, and the accuracy of the smoothbore gun and its high velocity APDS ammunition continued to be unsatisfactory. The T95E6 turret was to be made with the advanced silicas armor but was never constructed. All this led to the closure of the T95 project on July 7, 1960. But the T95E7 turret design using conventional hardened steel armor was carried forward, becoming the M60A1's turret.

The course of the M48 Patton's tank production was the source of widespread Congressional debate. The Bureau of the Budget believed that the Army was not progressing with sufficient speed in its tank modernization program and recommended the immediate replacement of the M48A2. Correctly predicting that Congress would not approve the procurement of the M48A2 after the fiscal year 1959, the Deputy Chief of Staff, Logistics (DCSLOG) proposed a tank based on the M48A2 featuring improved firepower and the AVDS-1790 engine. Since the main gun had not yet been specified, four XM60 weapons systems were submitted in September 1957.

The first concept was armed with the 120mm gun T123E6 in the long nosed T95E6 turret. This was the design preferred by the Ordnance Department. It was fitted with a mock-up of the new designed full-vision commander's cupola. A full sized prototype of this turret was constructed before this concept was dropped, mainly due to its slow rate of fire. The second carried the 105mm rifled T254E1 main gun in the T95E5 type turret and the T9 cupola style of the M48A2. The T254 guns used British X15/L52 barrels with a concentric bore evacuator on the barrel.

The Army Ordnance Technical Committee chose this design for production in August 1958. The third concept was to mount the 90mm T208 smooth-bore main gun and the T95E6 turret with the T6 cupola of the T95 tank. It never progressed beyond design drawings. The fourth used the T95E1 turret and the T208 main gun. A mock-up was built using the new vision cupola. All of these conceptual designs were referred to as the XM60. A contract was awarded to Chrysler Engineering in September 1958 for the advanced production engineering (APE) of the XM60 concept #2.

The T95 hull was considered however its one-piece front casting was too difficult and expensive to produce in quantity. Some existing T95 hulls were re-fitted with the AVDS-1790 engine and used from 1960 to 1964 to develop the T118E1 prototyping of the M728 Combat Engineer Vehicle. Instead the decision was made to use modified M48A2 hulls. The hulls had 3 return rollers and 6 steel roadwheel pairs per side with no shock absorbers, using only bumper springs on the first and sixth roadwheel arms, along with a widened turret well and ring, and a flat wedge-shaped glacis. The T254E2 gun was chosen to be the main weapon of the tank in August 1958 being standardized as the M68 105mm gun. After a briefing on 11 December 1958, General Maxwell Taylor ordered the XM60 into production because of the improvements it offered in firepower, protection, and cruising range.

Since the tank had not yet received its official designation these prototype hulls were briefly referred to as the M68 in December 1958 until they were officially named the M60 in March 1959. Fulfilling this requirement was an interim tank design that resulted in the M60-series, which largely resembles the M48A2 Patton it was based on, but has significant differences. The visual similarity of these designs as well as their overlapping period of service has caused some sources to informally name the original variant of the M60 as a Patton tank.

The original variant of the M60 series ultimately was produced as a quick fix engineering (QFE) upgrade of the M48 due to the Soviet Union's tank advancements of the late 1950s and the delays from developing the silicas armor and an improved turret design. The M60 mounted a 105 mm M68 main gun with the bore evacuator mounted towards the middle of the tube carrying 57 rounds in the clamshell shaped turret style of the M48. Nine rounds were stowed in the left side of the turret bustle behind the loader.

The remaining rounds were stored inside safe containers on the hull floor. A new short receiver coaxial machine gun was designed for the M60 tank. This was the 7.62mm M73/T197E2 which replaced the .30 caliber M37 used on the M48A2. It had 2,000 rounds of ammunition. They had a reputation for jamming. After working to correct this, they were redesignated as the M73A1 in 1970.

The electronics package on the M60 was essentially the same as used on the M48A2C including an improved turret control system and an all-metric measurement M16 Fire Control System (FCS), The M16 FCS consists of a new M10 ballistic drive and mechanical M16E1 gun data computer which integrated barrel temperature data with an M17 coincidence range finder. The rangefinder is a double image coincidence image instrument used as the ranging device of the gunner's primary direct sighting and fire control system. The gunner is provided with an M31E1 day periscope with a magnification of x8 and an M105D day telescopic sight with a magnification of x8 and a field of view of 7.5 degrees.

Range information from the rangefinder is fed into the ballistic computer through a shaft. The ballistic computer is a mechanically driven unit that permits ammunition selection, range correction, and superelevation correction by the gunner. The ballistic drive receives the range input and, through the use of cams and gears, provides superelevation information to the superelevation actuator. The superelevation actuator adds sufficient hydraulic fluid to the elevating mechanism to correctly position the gun.

In late 1962 a kit was fielded that allowed the use of the AN/VSS-1(V)1 IR searchlight. The searchlight has both infrared and visible light capabilities and was positioned over the gun. Along with an M32 IR periscope for the gunner, M19 IR periscope and M18 IR binoculars for the commander provided first generation night vision capability to the M60 and M60A1 tanks. This kit was also compatible with the M48A3/A5.

The hull bottom had a strong boat-like appearance with a pronounced recess between the upper tracks and external suspension arms with cast aluminum roadwheels and return rollers along with a single shock absorber on the first roadwheel pair. Cast aluminum road wheels were used to save weight. The armor was improved, at 6 inches (155 mm) on the front glacis and mantle of solid rolled homogeneous armor, while it was 4.3 inches (110 mm) on the M48. Power was provided by the AVDS-1790-2A engine, CD-850-5 cross drive transmission and the T97E2 track assembly as used on the M48A3.

The drive sprocket is located at the rear of the hull. The vehicle also provides full NBC protection for the crew using the M13A1 protection system creating a positive atmospheric pressure in the crew compartment. The positive pressure keeps contaminated air out and forces the smoke produced from firing the main or coax guns out of the vehicle. Access between the driver's compartment and the turret fighting compartment was also restricted, requiring that the turret be traversed to the rear.

The M60 was deployed to West Germany to counter the threat presented from the T-54s and T-55s of the Soviet Union and Warsaw Pact as well as to South Korea but was never sent to South Vietnam mainly due to unfavorable terrain and the general lack of significant numbers of North Vietnamese armor. In May 1961 Army Chief-of-Staff General George Decker announced that the European Command had been receiving the M60 to replace older tank inventory. By October the Seventh Army was outfitted with many of the tanks. A total of 2,205 M60s were built between June 1959 and August 1962. Some M60/E60 tanks were later transferred to Israel and participated in the Yom Kippur War. Some were repurposed as AVLBs.

### M60A1 series

Development
The program to develop the M60A1 was approved in early 1960 in conjunction with abandoning further development of the advanced composite armor and the closure of the T95 Medium Tank project. The first proof of concept attempt to mate a modified M60 hull with the T95E7 turret took place in March 1960. The turret, even without the siliceous cored armor, provided improved ballistic protection. Additional space for the turret crew was also made available by using the M140 mount thus moving the cannon 5 inches forward.

The first two prototypes (Pilot 1 and 2) were ready in May 1961 and the third (Pilot 3) in June 1961, when the vehicle also received its official prototype designation as the M60E1. These vehicles were built by Chrysler Defense. Pilot 1 was sent for evaluation at the Eglin Air Force Base climatic hangar, while Pilot 2 was tested at the Yuma Test Station, and Pilot 3 underwent field trials at Fort Knox.

On 22 October 1961, the M60E1 was officially accepted in service under the designation of Tank, Combat, Full Tracked: 105-mm Gun, M60A1. Production began on 13 October 1962 when the Army placed an initial order for 720 of the tanks for 61.2 million dollars.

Features
In addition to the new turret design, the hull was upgraded. The hull's upper glacis armor was increased from 3.67 inches to 4.29 inches at 65 degrees while the turret sides went from 1.9 inches to 2.9 inches at their apex. This brought the frontal armor up to the same 10" line of sight armor standard of the M103 heavy tank. A mushroom-shaped fume extractor was placed at the rear left of the turret bustle to vent smoke produced from firing the main or coax guns out of the vehicle. The addition of a shock absorber on the second roadwheel pair was also accompanied by a slight relocation of the first return roller. These modifications were needed due to the increased weight of the M60A1 turret as well as the additional hull armor.

The ammunition load for the main gun was increased to 63 rounds. Round storage was distributed between the turret bustle, where 15 ready rounds of various types were stowed and accessible for the loader, and the rest were stored inside safe containers on the hull floor.

The uncomfortable wire mesh seats for the loader and gunner were replaced with padded ones. The brake and accelerator pedal and gauges were also rearranged for more efficient and comfortable operation while the steering wheel was replaced by a T bar steering control. The engine and power train were supplied by the Continental AVDS-1790-2A engine and the CD-850-5 cross drive transmission and using the T97 track assembly.

Improvements to the electronics package for this version included an improved electro-mechanical traverse assembly and an AN/VSS-1(V)1 IR searchlight above the gun shield. The M19 FCS consisted of the M17A1 coincidence rangefinder, M10A1 ballistic drive and the mechanical M19E1 ballistic computer for the gunner. The M60A1 RISE Passive tank uses the M68E1 variant of the gun carried in the M140 mount. Most M60A1 RISE tanks were retrofitted to this standard after 1977. 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.

Upgrades
As the development of a new main battle tank stalled with problems and cost escalating quickly, the M60A1 was forced to serve longer than originally intended with production lasting almost 20 years. In that time span, numerous product improvement programs were put forward. As the major changes were incorporated into the production line, the vehicle model designations were changed. The first of which was Top Loading Air Cleaner (TLAC) in 1971. This reduced dirt and dust ingestion, which increased engine life as well as allowing for easier servicing of the engine. Early TLAC panels were made from aluminum and were vulnerable to damage from small arms fire.

Next came Add-On Stabilization (AOS) that was introduced in late 1972. This was an add-on kit made to fit with minimum modifications to the existing hydraulic gun control system. The add-on-stabilization system provides stabilization control for both gun elevation and turret traverse. It provides the gunner with the capability of aiming and target tracking and also improved surveillance of the battlefield terrain by the gunner while the tank is moving. It may be used in any one of three modes of control: (1) power-with-stabilization-on, (2) power-with-stabilization-off, and (3) manual. In the power-with-stabilization-on mode, the gunner's aim on target is automatically retained while the vehicle is in motion. This mode provides a fire-on the-move capability. The power-with-stabilization-off option eliminates needless exercise of the stabilization system and provides a backup power mode. The manual back up system permits the crew to aim and fire the weapons should the electrical/hydraulic subsystems fail.

At a range of 2000 meters, hit probabilities of better than 70% from a moving M60A1 were obtained in Aberdeen test results while without a stabilizer it was essentially zero. M60A1s with this upgrade were designated as the M60A1(AOS). The T142 track was fielded in 1974 which had replaceable rubber pads, better end connectors and improved service life. M60A1(AOS)+ was the denotation for M60A1s equipped with the TLAC & AOS upgrades and the T142 track.

Introduced in 1975, the Reliability Improved Selected Equipment (RISE) was a comprehensive upgrade of the M60A1 hull as well as integrating the previous TLAC and AOS upgrades. It included the upgraded AVDS-1790-2C RISE diesel engine and CD-850-6 transmission that featured several changes in order to improve service life and reliability. A new 650 ampere oil-cooled alternator, a solid state regulator and new wiring harness with more accessible disconnectors was also incorporated into the hull's electrical system as well as armored steel TLAC panels and the return to the use of steel roadwheels and return rollers. They were denoted as M60A1(RISE).

The 1977 fielding of the passive M32E1 sight for the gunner and M36E1 periscope for the commander as well as the M24E1 IR night vision block for the driver provided second generation night vision capabilities for M60A1 and RISE tanks. These new passive gunner's sight and commander's periscope provide recognition capability at longer ranges and at relatively low night light levels (1/2 moonlight). Under starlight conditions, they will provide recognition beyond 500 meters with the use of an IR searchlight.

During 1978 kits for the mounting of the M239 smoke grenade launchers and the mounting of the M240 as the coaxial machine gun were fielded. The development of the M735 APFSDS ammunition required a cam update to the gun's mechanical ballistic drive for accurate firing. M60A1s configured to this standard were denoted as M60A1(RISE)+

The M60A1(RISE) Passive featured the implementation of all previous updates plus Kevlar spall liners for the turret, AN/VVS-2 passive night vision block for the driver, a deep water fording kit, the capability to mount Explosive Reactive Armor (ERA) and the AVDS-1790-2D RISE engine with CD-850-6A transmission and a Vehicle Engine Exhaust Smoke System (VEESS) that visually obscured the area around the vehicle. The VEESS smokescreen system does not provide protection against infrared, thermal or laser detection.

The two six-barreled, electronically fired M239 smoke grenade launchers, one on each side of the main gun and replacement of the coax machine gun with the M240C were implemented in late 1978. The smoke grenades contain a phosphor compound that masks the thermal signature of the vehicle to the enemy. They were denoted as M60A1(RISE) Passive.

Over the period of M60A1 tank production, several essential engineering changes were incorporated. Many of these miscellaneous changes are to improve the system safety, reliability, maintainability and increase mission performance. The M60A1 Tank Hull/Turret Product Improvement Plan (PIP) Update Kit includes those items that could not be readily identified with basic major product improvements and to incorporate essential engineering changes that had occurred during M60A1 tank production. The update program included engineering changes and minor product improvements which were not part of specific product improvements, but were required to upgrade early vintage M60A1 tanks up to the current M60A1(RISE) production configuration. Additionally the Hull PIP Update Kit was applied to the M48A5.

The M60A1 was in production from October 1962 until May 1980 and was extensively used by the US Army and Marine Corps as well as being widely exported to foreign governments. A total of 7,948 M60A1s (all variants including E60A) were built. Many of them were later converted to the A3 standard.

### M60A2

During the early 1960s there was some debate regarding the future of main tank weaponry, largely focusing on conventional kinetic energy rounds versus missiles. In the early 1960s it was generally accepted that the maximum effective range of the M68 gun was between 1800 and 2000 meters. The XM-13 missile system had proven itself viable, obtaining over 90% first round accuracy up to 4000 meters. But the development of a main battle tank variant was bogged down by having too many design proposals. In response, studies were made in August 1961 to retrofit existing M60 tanks with a weapon capable of firing both conventional HEAT (High-Explosive Anti-Tank) rounds and launching ATGMs (Anti-Tank Guided-Missiles).

Three M60E1 tanks with T95 turrets were modified to permit the installation of the 152mm XM81 gun-launcher. Mounted on former M60 hulls, they were to provide test beds for the evaluation of the Shillelagh weapon system. Although this system was the preferred armament for the MBT-70, by late 1961 problems with the XM13 missile required that the program be reorganized. The missile was reclassified as an applied research project and it was obvious that there would be some delay before it would be available for service.

On 10 January 1962, representatives from various ordnance organizations met at the Ordnance Tank-Automotive Center (OTAC) to review armament systems that might be suitable replacements, if the Shillelagh missile could not be developed in a timely manner. Time was particularly critical for the Armored Reconnaissance/Airborne Assault Vehicle (AR/AAV) (the XM551 Sheridan) which required a decision on the armament by April 1962. The possible delay was not as serious for the MBT-70 since the program was limited to conceptual design and component development. The requirements also differed for the tank because of its ability to carry a much heavier weapon system.

Several backup weapons were also under consideration and concept studies were prepared showing their application to the MBT-70 concepts. The 152mm gun-launcher XM81 also was considered without the missile depending only on the combustible case conventional ammunition. It was expected that the Shillelagh or some other missile then could be introduced at a later date.

The 105mm gun M68 as standardized for the M60 tank was considered as an alternate armament system. It had the advantage of being immediately available and its ammunition was already in production. Of the several turrets drafted, one of the earliest was the driver-in-turret integrated fighting compartment. This design was further developed using the MBT-70. Another proposal was a more compact turret design of the T95E7.

### Development

During the development of the M60A2, three different turret types were considered, the Type A, Type B and Type C. The Type A turret would be constructed based on the T95E7 turret and then further modified and produced as the Type B standard. The Type C turret was essentially a larger M551 Sheridan-style turret. A mock-up of this turret was built, but the design was never seriously considered and soon abandoned. All of these conceptual variants were referred to as the XM66.

On 10 January 1964, the Army reviewed all three variants and selected the Type A variant for further development. Initially two Type A turrets were built in 1964. The M60A1 hull was used starting in 1966 to develop the new compact turret design using the 152mm M162/XM81E13 rifled barrel main gun. These developmental tanks were designated as the M60A1E series.

The M60A1E1 referred to vehicles based on the modified T95E7 Type A turrets with M60 hulls used through 1965. The M60A1E1 variant was used to evaluate the XM81 dual purpose gun and its compatibility with the XM13 Guided Missile, Armor Defeating together with the XMTM51 training round. During the early testing of the XM81 main gun it was noted that misfires and premature detonations of the M409 conventional case ammunition were caused by unburnt propellant in the bore and breech.

This flaw was often catastrophic as it set off the projectile in the barrel as it was fired. To remedy this the guns were equipped with a traditional fume extractor on the barrel. The XM81 Gun/Launcher also experienced frequent faulty breeches, often not closing correctly during a missile firing, allowing the exhaust of the launching Shillelagh to vent hot noxious gases into the crew compartment.

As the M60A1 hull became available in 1966, it was decided to upgrade these prototype vehicles to the M60A1 hull standard. Vehicles using the M60A1 hull and chassis received the M60A1E2 designation, and were used to develop the Type B compact turret and the XM81E13 gun variant. The M60A1E2 finalized the turret design with the use of a compact turret which reduced exposed frontal area by 40% compared to the M60A1 and continued development of the M51 Missile Guidance System (M51MGS).

These were later standardized as the M60A2. Initial plans called to retrofit the turret of every M60 with the new A2 turret, and use them in the mobile anti-armor role alongside the M60A1 tanks. But the continual technical and reliability difficulties with the dual purpose gun caused this to be abandoned. The M60A1E3 variant was a prototype mounting the M68 105 mm rifled gun to the turret of the M60A1E2. This was evaluated due to several earlier faults noted in the M60A1E1's main gun. Compared to the Shillelagh system, the use of the 105mm gun increased the overall tank weight by about 1,700 pounds (770 kg).

The M60A1E4 was a conceptual variant that explored the use of various remote controlled weapons, including a 20mm gun as secondary armament. A mock-up of this design using the Type C turret was constructed. All variants of this series underwent evaluations and trials at the Aberdeen Proving Ground. The M60A1E2 was finally accepted by the Army in 1970 and given the designation Tank, Combat, Full Tracked: 152-mm Gun/Launcher, M60A2.

Initial orders were submitted by the Army in 1971 however production did not start until 1973 and continued until 1975. All were built at the Chrysler Tank Plant in Warren, Michigan with a total of 540 M60A2s produced. The M60A2 was intended to serve as the stop-gap solution until its projected replacement, the MBT-70 completed its development. The M60A2 was deployed to Army units in Europe starting in June 1975 when B Company, 1-32 Armor Battalion received its first M60A2 tanks.

### Features

The M60A2 featured a unique low profile turret, mounting the M162 Gun/Launcher that drastically reduced the turret's frontal arc in comparison to the A1's. It consisted of a large disk with a narrow channel in the center with each crew member in the turret having their own hatch. The gunner and loader were located to the right and left of the gun, respectively, and the commander was in a turret basket up and behind the main gun.

As a result, each crew member was effectively isolated from one another with the gunner and loader separated by Shillelagh missiles in their storage position. The commander was in the rear compartment under a large redesigned cupola, which somewhat negated the low profile silhouette of the turret.

The M162 gun was fully stabilized in both turret traverse and gun elevation using the same upgrade kit as the M60A1 AOS, allowing the gunner to effectively scan the battlefield while the tank was in motion. This system could be used by the gunner to engage targets with unguided M409 rounds while the vehicle was in motion, but the tank had to remain stationary when firing and tracking an MGM-51 missile. The turret interior also received Kevlar spall liners. Four M226 smoke grenade launchers were mounted on each side of the turret bustle.

Additionally there was a mounting point on the left side of the turret for an AN/VSS-1(V)1 Infrared Spotlight and M19E1 IR periscope providing first generation night vision for night operations. A basket was fitted to the rear of the turret to stow the spotlight when not in use. Late production versions replaced the bore evacuator with the Closed-Bore Scavenger System (CBSS), a compressed air system that pushed the fumes and gases out of the muzzle when the breech was opened.

Initial production M60A2s used the M60A1 hull powered by an AVDS-1790-2A TLAC engine, CD-850-5 cross-drive transmission and the T97 track assembly. Many of these hulls were later upgraded to the RISE standard.

The M51 Missile Guidance System (MGS) for the Shillelagh missiles was designed by Ford's Aerospace Division. The M51 MGS consisted of an infrared (IR) direct beam guidance and control system to track the missile mounted to the turret over the mantel of the gun with a telescopic sight and a Raytheon AN/WG-1 Flashlamp Pumped, Ruby Laser range finder, accurate to 4,000 meters, for the gunner.

The gunner aimed the cross-hairs in his direct telescopic sight at the target and fired the missile. After acquiring a target a small charge would propel the missile out of the barrel. The missile's solid-fueled sustainer rocket then ignited and launched the Shillelagh. For the time of flight of the missile, the gunner had to keep the cross-hairs pointed at the target. A direct infrared beam missile tracker in the gunner's sight detected any deviation of the flight path from the line-of-sight to the target, and transmitted corrective commands to the missile via an infrared command link. The MGM-51A was stabilized by flip-out fins, and controlled by hot gas jet reaction controls.

The gunner also employed an M219 (later replaced with a M240C) to the gun mantle's right with 2,000 rounds. The commanders cupola was redesigned causing the M85 to be mounted in the inverted position in order to provide access to its feed cover and mounted a single M34 periscope carrying 600 rounds. The M60A2's combat load for the M162 main gun consisted of 33 M409 rounds and 13 MGM-51 Shillelagh missiles.

Flaws
This weapon system had several drawbacks. First the gunner had to keep the target in the crosshairs of the sight during the entire flight time of the missile. This meant that only one target could be tracked and engaged at a time. Furthermore, the M60A2 could not fire or track a missile while moving.

Secondly was the high minimum range of about 730 m (2,400 ft). Until the missile reached this range it flew beneath the tracking system's infrared beam and could therefore not be guided by the infrared command link. Also minimum range was slightly above the maximum effective range of the M60A2's conventional unguided munition. This created a dangerous gap area that could not be adequately covered by fire known as a "dead zone".

It was also discovered that structural cracks in the barrel occurred after several missile firings. This defect was traced to a flaw in the missile's longitudinal key, which fitted into a keyway inside the gun barrel. It was determined that a less deep key would significantly extend the service life of the barrel.

The Missile Control System was also very fragile owing to its dependence on vacuum tubes which often broke when firing the gun. Finally a Shillelagh missile was considerably more expensive than the M409 round. The vehicle was one of the most technologically complex of its era, eventually garnering an unofficial nickname of "Starship". This also contributed to its failure, largely due to difficulties with maintenance, training, and complicated operation.

The M60A2 proved a disappointment, though its technical advancements would pave the way for future tanks. Its intended successor, the MBT-70, was canceled in 1971 and its funding diverted into the conceptual development of the XM1 Abrams. The Shillelagh/M60A2 system was phased out from active units by 1981, and the turrets scrapped. The main replacement for the Shillelagh missile in the mobile anti-armor role was the more versatile BGM-71 TOW. Most of the M60A2 tanks were rebuilt as M60A3s, or the hulls converted to armored vehicle-launched bridge (AVLB) vehicles and M728 Combat Engineer Vehicles with a few M60A2s retained as museum pieces.

### Development

Due to the rapidly developing advancements in anti-armor capabilities and solid-state electronics of the 1970s, along with the general dissatisfaction of the M60A2, an upgrade of the M60A1 was needed. In 1976 work began on the M60A3 variant which featured a number of technological enhancements and increasing the turret armor.

### Features

The M60A3 version of the M60-series had the same mobility, performance, and weapons systems as the M60A1 RISE and RISE Passive tanks and incorporated all of their engineering upgrades, improvements and capabilities. In addition, the armor protection for the turret was increased to 330 mm on the gun mantle and to 276 mm on the turret face.

The electronics and fire control systems were greatly improved. The turret's hydraulic fluid was replaced with a non-flammable one. This updated turret configuration was mated to the M60A1 RISE hull using the AVDS-1790-2D RISE engine and CD-850-6A transmission along with a Halon fire suppression system. It was designated as the Tank, Combat, Full Tracked: 105-mm Gun, M60A3.

The M60A3 tank was built in two configurations. The earlier version, sometimes referred to as the M60A3 Passive, uses the same passive gunner's sight as the A1 RISE Passive and the latest version has a Tank Thermal Sight (TTS). The M60A1, RISE, and RISE Passive tanks used a coincidence rangefinder and the mechanical M19 ballistic computer. The M60A3 uses a laser based rangefinder and the solid state M21 ballistic computer.

The M21 FCS for the M60A3 was made up of a Raytheon AN/WG-2 flash-lamp pumped ruby-laser based range finder, accurate up to 5000 meters for both the commander and gunner, a solid-state M21E1 gun data computer incorporating a muzzle reference sensor and crosswind sensor, ammunition selection, range correction and superelevation correction were inputted by the gunner, an improved turret stabilization system along with an upgraded turret electrical system and solid-state analog data card bus. The M10A2E3 ballistic drive is an electro-mechanical unit.

The commander had an M36E1 passive periscope and the gunner an M32E1 passive sight. The TTS configuration replaced the gunner's sight with the Raytheon AN/VSG2 Tank Thermal Sight (TTS), a Mercury-Cadmium-Telluride (HgCdTe) IR detector. This sight allows the gunner to see through fog, smoke and under starlight conditions without the aid of an IR searchlight. This system provided improved night fighting capabilities.

The first M60A3s were assembled at the Detroit Arsenal Tank Plant in February 1978 where the first of a low-rate of initial production quantity of 296 M60A3s were produced through October with fielding to Army units in Europe starting in May 1979. The M60A3 was seen by the US Army as a stop-gap measure as the development of the XM1 Abrams MBT was already well advanced with fielding to Europe planned to start in 1981 and notified Foreign Military Sales (FMS) customers of its near-term plans to discontinue M60-series tank production.

In March 1982 General Dynamics Land Systems purchased Chrysler Defense. The procurement of M60A3 and M60A3 TTS tanks for the Army concluded and hull production ceased in May 1983 with a total of 1,052 M60A3 and TTS tanks built as new vehicles. However the conversion of earlier models to M60A3/E60B tanks continued for FMS with the last tanks delivered to Israel in May 1986 and a conversion total of 3,268 E60Bs. These late-production examples were upgraded from existing surplus inventories of M60A1 RISE tanks.

The Army also increased its M60A3 TTS fleet through the M60A1 Product Improvement Program (PIP) and the M60A3 tank field retrofit program conducted by the Anniston Army Depot and the Mainz Army Depot (MZAD). Depot field teams retrofitted all of the Army's 748 M60A3 tanks to the TTS configuration by the end of 1984. In addition, both depots converted a total of 1,391 M60A1 RISE tanks to the M60A3 TTS. These M60A1 RISE PIP conversion programs concluded in 1990.

Italy, Austria, Greece, Morocco, Taiwan and other countries upgraded their existing fleets with various E60B component upgrades under several FMS defense contracts with Raytheon and General Dynamics during the mid to late 1980s. In 1990, M60A3/E60Bs from Army surpluses were sold to Oman, Bahrain, and Saudi Arabia.

The M60A3 replaced the M60A1 in the US Army and any remaining M48A5s in ARNG service on a one-for-one basis. The Marine Corps continued to use the M60A1 RISE Passive until they were withdrawn from combat use in 1991. They were phased from ARNG service between 1994 and 1997, being replaced with the M1 MBT. The Detroit Tank Plant was closed in 1996 with production of the M1A1 Abrams continuing at the Lima Tank Plant in Ohio.