M103 (heavy tank)

M103 heavy tank
An M103A2 in the Lewis Army Museum in 2015
TypeHeavy tank[1]
Place of originUnited States
Service history
In service1957–1974
Production history
No. built300
VariantsM103A1, M103A2
Mass65 short tons (58 long tons; 59 t)
Length37 ft 2 in (11.33 m)
Width12 ft 2 in (3.71 m)
Height10 ft 6 in (3.20 m)
Crew5 (commander, gunner, driver, 2 loaders)

Armor127 mm (5 in) @ 60 degrees[2]
254 mm LoS (10 in)
120 mm gun M58, 34 rounds
2×.30-cal (7.62 mm) M1919A4E1 machine gun
1×.50-cal (12.7 mm) M2 AA machine gun
Engine(M103A1) Continental AV1790 12-cylinder air-cooled gasoline
810 hp (604 kW) 
(M103A2) Continental AVDS-1790-2, V12, air-cooled, twin turbocharged diesel
750hp (560kW)
Power/weightM103A2: 12.7 hp (9.5 kW) / tonne
TransmissionGeneral Motors CD-850-4A or -4B, 2 ranges forward, 1 reverse
Suspensiontorsion bar
Fuel capacity280 US gallons (710 liters)
M103: 80 mi (130 km)
M103A2: 295 mi (480 km)
SpeedM103: 21 mph (34 km/h)
M103A2: 23 mph (37 km/h)

The M103 Heavy Tank (officially designated 120mm Gun Combat Tank M103, initially T43)[3] served in the United States Army and the United States Marine Corps during the Cold War. The last M103s were withdrawn from service in 1974. The M103 was the last heavy tank to be used by the US military as the concept of the main battle tank evolved, making heavy tanks obsolete.

Design and development

In December 1950 the Army made blueprints for a heavy tank reference design.[4] In January 1951 the Army awarded Chrysler a $99 million contract to produce the tank.[5] Chrysler tasked Robert T. Keller, the son of Chrysler Board Chairman K.T. Keller, with overseeing the design of the tank and construction of the Newark tank plant that would be used to produce it.[4]

The first T43 pilot model was completed in November 1951 at the newly built Chrysler tank plant in Newark, Delaware. Officials said the tank would "out-slug any land-fighting machine ever built."[6]

Like the contemporary British Conqueror tank, the M103 was designed to counter Soviet heavy tanks, such as the later IS-series tanks or the T-10 if conflict with the Soviets broke out. Its long-ranged 120 mm cannon was designed to hit enemy tanks at extreme distances.

In 1953–54 a series of 300 tanks, initially designated T43E1, were built at the Newark plant. Specifics about the tank, including production plans and specifications, were kept secret. Seeking to keep the tank out of public sight, Secretary of Defense Charles E. Wilson nixed an October 1953 exhibition for the American Ordinance Association at Aberdeen Proving Ground.[7] In May 1954 the tank was debuted publicly at a demonstration at the Newark tank plant.[8]

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 become heir to any additional T43 orders after Chrysler tank production wrapped up in June 1954.[9]

Testing was unsatisfactory; the tanks failing to meet Continental Army Command's standards and the tanks were put into storage in August 1955. After 98 improvement modifications were approved, in April 1956 the tank was designated the M103 Heavy Tank.[10] 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 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.[11]

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 28-inch (71 cm) 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 810 horsepower (600 kW) and 1,600 pound force-feet (2,200 N⋅m) 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 34 kilometres per hour (21 mph) 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 80 miles (130 km). 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 (250 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 221-millimetre (8.7 in) of 30-degree sloped rolled-homogenous armor at 1,000 yards and 196-millimetre (7.7 in) at 2,000 yards. It could also penetrate 124-millimetre (4.9 in) 60-degree sloped rolled-homogenous armor at 1,000 yards and 114-millimetre (4.5 in) 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.

The crew of an M103A1 consisted of the driver (1), the gunner (2), the two loaders (3 & 4) and the commander (5).
Aspect Thickness Angle to vertical
Hull front, upper 5 inches (127 mm) 60 degrees
Hull front, lower 4.5 inches (114 mm) 50 degrees
Hull side, upper equals 2 inches (51 mm) 40 degrees
Hull side, lower equals 1.75 inches (44 mm) 30 degrees
Hull top 1 inch (25 mm) 90 degrees
Hull floor, front 1.5 inches (38 mm) 90 degrees
Hull floor, rear 1.25 inches (32 mm) 90 degrees
Turret mantlet 10 to 4 inches (254 mm to 102 mm) 0 to 45 degrees
Turret front 5 inches (127 mm) 50 degrees
Turret side 5.38 to 2.78 inches (137 mm to 70 mm) 20 to 40 degrees
Turret rear 2 inches (51 mm) 40 degrees
Turret top 1.5 inches (38 mm) 85 to 90 degrees
Other Languages
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日本語: M103重戦車
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