The M4 Sherman was undoubtedly the face of the American armored corps during World War 2 (1939-1945). The vehicle was introduced in 1942 and saw production into 1945 with over 49,200 of its type manufactured (including a myriad of variants). Its availability was such that the tank made up many foreign tank stocks during and after the war with the last known frontline examples not retired until the 1960s/1970s. Despite this impressive service tenure, the M4 was something of an obsolete product even by 1944 standards particularly with the arrival of the new generation of German medium/heavy tanks (the Panzer V, VI, and VIB) of the war. Additionally, the Soviets - set to become the West's direct post-war threat - were finding success with their T-34 medium and "Josef Stalin" heavy tanks (the IS-2).
The United States Ordnance Department began looking towards the future even as the M4 Sherman was settling in as the standard American medium tank of the war. This led to several design initiatives all of which eventually fell to naught for the M4 was proving a capable mount in number despite its limited main gun and overall battlefield performance. In 1942, work began on a new product through the "M4X" program that begat a possible M4 Sherman successor in the "T20". However, this endeavor ultimately other attempts at replacing the M4 for it was not selected for formal service. The T20 line - encompassing four developmental tanks - differed primarily in armament, suspension, and transmission systems in play. A shortened drive shaft was used to help the vehicle promote a shallower profile.
Compared to the wartime Sherman, the T20 exhibited more of the fine lines of a modern combat tank of the 1950s. Its turret was held well-forward along the shallow hull superstructure and promoted some barrel overhang ahead. The glacis plate was short but well angled for basic ballistics protection. The engine resided at the rear of the hull and the main armament was sat within a 360-degree traversing turret. A pair of crew hatches were located at the front hull roof with a pair of hatches along the turret roof. The crew numbered five and included a driver, co-driver/bow machine gunner, commander, gunner, and loader - the crew of five consistent with many combat tanks of the period. Armor protection reached 62mm and the vehicle weighed in the 33-ton range (short). Dimensions included a length of 5.7 meters, a width of 3 meters, and a height of 2.44 meters. Power was served through a Ford GAN V-8 gasoline-fueled engine of 470 horsepower output which offered road speeds of 40 kmh and an operational range of 160 kilometers.
All versions would have featured a .30 caliber M1919 Browning coaxial machine gun alongside the main gun as well as a .30 caliber M1919 in a ball mounting at the front-right side of the glacis plate. An optional 0.50 caliber M2 Browning heavy machine gun on a pintle mounting along the turret roof was envisioned for local anti-aircraft defense. 6,000 rounds of .30 caliber ammunition were to be carried aboard. The main gun would have been fed form a stock of about 70 shells depending on main gun installed.
The four T20 forms began with the base T20 pilot vehicle which featured a problematic Hydramatic transmission system along with a more potent 76mm main gun armament (the original M4 Sherman's 75mm gun proved lacking against the latest German tanks). Subsequent T20 models changed the primary armament and suspension system: The T20E1 was to carry the 75mm main gun and have a Horizontal Volute Spring Suspension (HVSS) suspension though this model's development was ended and its turret carried over to the upcoming developmental T22E1 mark. The T20E2 was given a 76mm main gun and a more common torsion bar suspension arrangement. Additional work then evolved the T20E2 pilot vehicle into the T20E3 mark, carrying over the same gun and suspension system.
None of the aforementioned T20 vehicles were adopted for serial production for it was deemed by authorities that the M4 Sherman was seemingly up to the task of helping to end the war. Work continued along other avenues such as in the related T22 which fielded a 76mm main gun and HVSS suspension system. The T22E1 joined it though with a 75mm main gun and the original M4 Sherman mechanical transmission system. Yet another program variant related to the T20 was the T23/T23E3 which fitted an electric transmission and were both were armed with a 76mm main gun. Even these were not impressive enough to be selected as the M4's successor to which the work eventually culminated with the M27 but, again, authorities were satisfied with their massive stocks of M4 Shermans.
American World War 2 tank development reached its apex during the war years with the arrival of the M26 "Pershing" Heavy Tank available in only limited numbers in Europe by the end of the war. This line saw additional service in the Korean War, a conflict which finally showcased an all-new generation of American medium tanks through the M46, M47, and M48 "Patton" lines. The M46 itself was developed as a successor to both the M4 Sherman and the M26 Pershing. The M47 was a further evolution of the M46 and, itself, served as the basis for the later M48. The Americans then added their first Main Battle Tank by adopting the M48-based M60 "Patton" in 1961 before moving on to the M1 Abrams of today.