In the years following World War II, the United States embarked on the development of heavy tanks. However, their initial endeavors in this direction faced setbacks. It was not until 1948 that the T43 project was initiated at the Detroit Arsenal, laying the groundwork for the eventual introduction of the M103 heavy tank, which would ultimately become America’s last heavy tank.

The T43 project featured a tank with significant sloped armor and a 120-mm muzzle gun designed to handle separating charges. The aim was to create a combat vehicle capable of countering potential enemy heavy tanks. Progress on this project was initially slow, with limited interest from the military. 

It wasn’t until the end of 1950, against the backdrop of the Korean War, that the technical project was completed. In early 1951, Chrysler was awarded a contract for constructing six prototype vehicles based on the T43 design.

The first tank underwent testing in November of the same year. These tests identified various shortcomings and issues, leading to the development of an improved version known as the T43E1. Simultaneously, work continued on refining the tank’s armament and ammunition. By October 1953, all modifications were complete, and the tank was poised for the next phase.

M103: America's Last Heavy Tank

By December of that year, Chrysler had already initiated production, managing to produce 300 improved T43E1 tanks by June 1954. Following this, efforts shifted towards converting the tanks into the M51 configuration. By 1955, 187 M51 tanks had been produced, but their independent testing phase proved inconclusive.

In terms of technical specifications, the T43E1 project solidified the heavy tank’s overall design. The tank featured a traditional layout with a 120-mm rifled gun and employed numerous off-the-shelf components. The tank’s body was composed of welded, cast, and rolled parts, with frontal armor reaching up to 127 mm and sloping at 60 degrees. The turret boasted 127-mm thick frontal armor and up to 254 mm on the gun mantlet. This armor was intended to protect the tank from enemy tank shells.

Under the hood, the tank was powered by a Continental AV-1790 gasoline engine, generating 810 hp, and originally sourced from the M48 tank. The tank had seven torsion bar suspension units on each side. The turret housed a 120-mm cannon T122/M58, with a long-barreled 60-caliber rifled barrel and a muzzle brake. The gun utilized separate charge shots, capable of propelling armor-piercing M358 projectiles at speeds of up to 1067 m/s. The tank carried 34 rounds of ammunition.

The tank featured an advanced fire control system, initially based on optics, which evolved over time with the addition of new components, including a ballistic computer. The tank’s armament also included two paired-barreled M1919A4 machine guns and one anti-aircraft M2. The crew consisted of five members, with the driver positioned inside the hull and the rest of the crew in the turret.

M103: America's Last Heavy Tank

The T43E1 tank weighed 58 tons, measuring 11.3 meters in length (with the gun forward), 3.76 meters in width, and 2.88 meters in height. Its estimated top speed ranged from 32 to 34 km/h, although its actual speed was often lower. The tank had a range of 130 km and could overcome various obstacles, thanks to its relatively lighter weight compared to other heavy tanks of its era.

The initial testing of the T43E1 revealed mobility and fuel consumption issues linked to its power unit, which was borrowed from medium tanks. Additionally, outdated fire control systems hindered the tank’s full potential. Consequently, the project was temporarily halted, and the tanks were placed in storage. A new round of modifications led to the creation of the T43E2 project, featuring an updated powertrain and weapon systems.

In 1956, it was decided to rebrand the tank as the 120 mm Gun Combat Tank M103. However, only 74 of these modified tanks were produced in 1956-57. Subsequently, the Marine Corps expressed interest in acquiring 219 (or 220, according to some sources) heavy tanks, initiating another round of modernization.

Starting in 1959, these upgraded tanks were designated as M103A1. The “A1” project incorporated the installation of the T52 gunner’s stereo sight and the M14 ballistic computer. Changes were made to the turret’s electrical rotation mechanism, and the tank was equipped with an ejection mechanism. One of the two machine guns was removed from the gun installation.

The final major modernization took place in 1964, commissioned by the Army. A total of 153 tanks were equipped with the M60 power unit, based on the Continental AVDS-1790-2 diesel engine, providing 750 hp. This increased the tank’s top speed to 37 km/h and extended its operational range to 480 km. Some fire control devices were upgraded, and these modernized tanks were designated M103A2.

Officially introduced in 1956, the M103 heavy tank took several years to be fully delivered and deployed. Initially, these tanks were assigned to various army units. By January 1958, the 899th Heavy Tank Battalion (later the 2nd Battalion of the 33rd Tank Regiment) equipped with M103 tanks was stationed in the Federal Republic of Germany. The battalion consisted of four companies, each with six sections, totaling 72 tanks, representing the entire available fleet of new heavy tanks for the Federal Republic of Germany.

However, issues with the M103 soon became apparent, including mobility problems linked to the diesel engine, reliability concerns, and inadequate interior design. Additionally, the tank lacked protection against weapons of mass destruction and faced redundancy against Soviet T-54/55 tanks. As a result, its usefulness in modern warfare was in question.

M103: America's Last Heavy Tank

By the early 1960s, the U.S. Army shifted its focus to the M60 main battle tank, which offered superior mobility and firepower. Consequently, the M103 was no longer a priority, and the era of heavy tanks came to a close. The M103 underwent several modernization phases, including the “A2” project, but eventually, in the early 1970s, even the Marine Corps transitioned away from these obsolete heavy tanks.

Thus, the T43/M103 heavy tank had a relatively short service life, lasting less than five years in the Army and three times longer in storage. Despite never seeing combat, these tanks participated in numerous maneuvers before being retired and, in some cases, preserved for display in museums. 

Today, around 25 tanks of the main modifications are known to have survived, finding homes in various museums and military bases across the United States. They stand as a testament to an era when heavy tanks played a significant role in armored warfare, paving the way for the evolution of main battle tanks as the new standard.