M103 heavy tank

Heavy Tank M103
An M103A2 at The Tank Museum in the UK
Type	Heavy tank
Place of origin	United States
Service history
In service	1957–74
Production history
Manufacturer	Chrysler
Number built	300
Variants	M103A1, M103A2
Specifications
Weight	65 short tons (58 long tons; 59 t)
Length	22 ft 8 in (6.91 m)
Width	12 ft 2 in (3.71 m)
Height	10 ft 6 in (3.20 m)
Crew	5 (commander, gunner, driver, 2 loaders)
Armor	127 mm (5 in) @ 60 degrees 254 mm LoS (10 in)
Main armament	120 mm gun M58, 34 rounds
Secondary armament	2×.30-cal (7.62 mm) M1919A4E1 machine gun (co-axial) 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/weight	M103A2: 12.7 hp (9.5 kW) / tonne
Transmission	General Motors CD-850-4A or -4B, 2 ranges forward, 1 reverse
Suspension	torsion bar
Fuel capacity	280 US gallons (710 liters)
Operational range	M103: 80 mi (130 km) M103A2: 295 mi (480 km)
Speed	M103: 21 mph (34 km/h) M103A2: 23 mph (37 km/h)

The M103 Heavy Tank (officially designated 120mm Gun Combat Tank M103) 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 The last M103s were withdrawn from service in 1974.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.

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 by Chrysler at the Newark plant. 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, on 26 April, 1956 the tank was designated the M103 Heavy Tank. 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.

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” 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 and 1600 foot-pound of torque, fed through a General Motors CD-850-4 3-speed transmission. This allowed the 60-ton heavy tank to achieve a maximum road speed of 34 km/h 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. Though this was partially corrected with the introduction of the AV-1790-2 diesel unit, it would remain cumbersome and gas-thirsty for the majority of its production life.