M103 (heavy tank)
The M103 Heavy Tank (officially designated 120mm Gun Combat Tank M103, initially T43) was a heavy tank that served in the United States Army and the United States Marine Corps during the Cold War. Introduced in 1957, it served through 1974, by which time evolution of the concept of a main battle tank had rendered heavy tanks obsolete. Design and development. In December 1950 the U.S. Army made blueprints for a heavy tank reference design. In January 1951 it awarded Chrysler a $99 million contract to produce the tank. Chrysler tasked Robert T. Keller, the  son of Chrysler Board Chairman K.T. Keller, with overseeing its design, and construction at the company's new Newark, Delaware, tank plant. The first T43 pilot model was completed in November 1951. Officials said the tank would "out-slug any land-fighting machine ever built." Like the contemporary British Conqueror, the M103 was designed to counter Soviet heavy tanks, such as the later IS-series tanks or the T-10 if conflict with the Eastern Bloc broke out. Its long-ranged 120 mm cannon was designed to destroy enemy tanks at extreme distances. Some 300 tanks were built in 1953–54, initially  designated T43E1. Details about the tank, including production plans and specifications, were tightly held. Seeking to keep the tank out of public sight, Secretary of Defense Charles E. Wilson nixed an October 1953 exhibition for the American Ordnance Association at Aberdeen Proving Ground. In May 1954 the tank was debuted publicly at a demonstration at the Newark tank plant. In 1953 the Pentagon began a reversal of the President Truman administration policy of a broad production base in favor of Wilson's "single, efficient producer" concept. In September Wilson chose General Motors over Chrysler to take over production of the  M48 Patton. General Motors would also become heir to any additional T43 orders after Chrysler tank production wrapped up in June 1954. Testing was unsatisfactory, with the tanks failing to meet Continental Army Command's standards and being put into storage in August 1955. Following the approval of 98 improvements the tank was redesignated the M103 Heavy Tank in April 1956. Of the 300 T43E1s built, 80 went to the US Army (74 of which were rebuilt to M103 standard), and 220 were accepted by the US Marine Corps, to be used as infantry support, rebuilt successively to improved M103A1  then M103A2 standards. A House Government Operations subcommittee report in July 1957 called for the heavy tank program to be audited. Investigators had been unable to determine the cost of the program, which was estimated in the hundreds of millions of dollars. The report said the Army had hastened production of the tank for war in Korea despite there being no need for it there. The tank was also unsuited to the rigors of the nuclear battlefield, the report said. Specifics. Following contemporary American design philosophy, the M103 was built with a two-piece, cast elliptic armor scheme, similar to  the M48's design. It featured seven road wheels per side, mounted with long-arm independent torsion bars. The track was shoed in steel backed rubber chevron tracks, allowing for a ground pressure of 12.9 psi. The Continental AV-1790 engine was placed at the rear of the tank, and produced a maximum output of and of torque, fed through a General Motors CD-850-4 two-speed transmission. This allowed the 60-ton heavy tank to achieve a maximum road speed of and a maximum climbing gradient of 60%. Initial production versions suffered a host of drivetrain mechanical problems. The Continental  powerpack, shared by the much lighter M48/M60 tanks, was insufficient to drive the much heavier M103. The resulting performance of the tank was dismal; being severely underpowered and very fuel intensive. This presented a host of logistical problems for the vehicle, most prominently the extremely limited range of just . Though this was partially corrected with the introduction of the AV-1790-2 diesel unit, it would remain cumbersome and fuel-thirsty for the majority of its service life. For ease of production, many of the large components of the tank were made from cast armor. This design scheme was also  much more mass efficient than traditional rolled plate armor. Despite being better protected than the T29-series of prototypes which preceded it, the M103 was nearly 10 tons lighter, making it competitive with the Soviet T-10/IS-8 tank. The frontal hull glacis was a compound pike, welded at the center seam, with up to 10 inches thick armor at the front. The turret was a massive single-piece cast design, fitted with heavily sloped 10-inch (254 mm) rolled-homogenous armor. The M103 was designed to mount the 120 mm M58 gun, fitted in the M89 turret mount. Using standard  Armor-Piercing Ballistic Cap Tracer Rounds, it was capable of penetrating of 30-degree sloped rolled-homogenous armor at 1,000 yards and at 2,000 yards. It could also penetrate 60-degree sloped rolled-homogenous armor at 1,000 yards and at 2,000 yards. The commander could select from 34 rounds of either M358 Armor-Piercing Ballistic Cap Tracer Rounds or M469 HEAT shells, mounted at the rear of the turret and in the hull. With both loaders, the maximum firing rate of the gun was five rounds per minute, owing to the design of the two-piece ammunition. Using the electrohydraulic  turret traverse, the gunner could turn the turret at 18 degrees per second, with 15 degrees of elevation and 8 degrees of gun depression. The armor was made from welded rolled and cast homogeneous steel of varying thickness. Service. US Army 7th Army wanted the new heavy tank to supplement its M48 tanks. In Europe, the US Army fielded only one battalion of heavy tanks, from January 1958, originally assigned to the 899th Tank Battalion, later re-designated the 2d Battalion, 33d Armor. The US Army heavy armor battalion, in contrast to other armor units, was organized into four tank  companies, composed of six platoons each, of which each platoon contained three M103s, for a total of 18 tanks per company. Standard US Army armor battalions at the time had three companies per battalion, each with three five-tank platoons, with 17 tanks per company (two tanks were in headquarters platoon). One of the flaws of M103 vehicle was it did not have adequate reliability in retreat operations. US Army was aware that more Tiger tanks had been lost during retreat operations than during actual combat, and US Army in Europe could not afford that. In Europe it was found  that the engine was underpowered, requiring replacement of engines and transmissions after only about 500 miles. In addition, the ammunition stowage was not convenient and repeated firing caused excess chamber erosion, tracks were easily thrown. Last but not least crew safety, comfort and ability to function were impaired by poor interior arrangement. The M103 was placed on the road to obsolescence when the US Army shifted to the concept of a single main battle tank optimizing firepower, protection, and mobility in a single medium tank design. The U.S. M60 tank fulfilled the breakthrough functions of M103 heavy tank while retaining  the mobility of M48 medium tanks. By that time it was years since US Army had realized Soviet heavy tanks were not as potent as suspected, and thus the M103s were rather overkill and expensive to deal with T-54/55 tanks. The US Marine Corps assigned one M103 company to each of its three Marine tank battalions, including its Marine reserve units. The M103 was never used in combat. While the US Army deactivated its heavy armor units with the reception of the new M60 series main battle tanks in 1963, the remaining M103s stayed within the US Marine Corps inventory  until they began receiving the M60 series main battle tank. With the disappearance of the heavy tank from US forces came the full acceptance of the main battle tank in 1960 for the US Army, and 1973 for the US Marine Corps. Although the later M1 Abrams main battle tank utilizes the same caliber of main gun, 120 mm, the M103's cannon was a rifled gun firing a separate-loading round, in which the projectile was loaded into the breech, followed by a cartridge case consisting of a brass case, primer, and propellant in a fixed unit. This separate -loading system necessitated the use of two loaders. The only part of the cartridge case consumed during firing was the propellant and a plastic cap on the end of the brass cartridge case. The spent brass cartridge case was ejected after firing. The M1 tank's 120 mm main gun is a smooth bore firing a semi-caseless round, ejecting only a back cap of the original loaded round; the bulk of the M1's 120 mm shell casing is consumed during firing. Ammunition. Ammunition for M103's M58 gun included: Surviving examples. Existing M103 and M103A2s include: M103 (heavy