Although never formally one of the Patton series, the M60 was developed as a result of the learning gained with the M46/47/48 tanks, which did bear the name. It first entered service with the US Army in 1960-61 and was the Main Battle Tank through to the end of the 1990s when it was replaced by the M1 Abrams.
Work on an improvement to the M48 design started in 1957. Compared to the M48, it was intended to be better armed (a 105mm gun instead of a 90mm gun), have better endurance thanks to a diesel engine and better armour. Early examples had the M48 turret, but this was superseded by a completely new design with a much reduced front profile.
The practice of ‘evolutionary development’ was well established in US tank development; in 1941 the M4 Sherman was based on a chassis originally designed for the M3 Grant/Lee, which in turn was based on suspension systems devised earlier. The gun was the British L5 which, at the time, was probably the best tank cannon in the world (although the Russians would no doubt differ on this). The transmission was the ‘Cross Drive’ system using a torque converter and was essentially a form of automatic. This had been proven as far back as the M26 Pershing of the late war period. The real novelty here was the engine. The US finally switched to diesel rather than petrol engines. Although the power of the engine was less than that of the petrol equivalent in the superseded M48, the M60 had the same performance and greater range.
As the chassis was, effectively, the result of a continuous development process since the M46, it was only to be expected that the M60 would be upgraded and its service life extended as long as possible. Successive upgrades saw armament and gun control improvements, armour and turret upgrades and other variants, notably engineer vehicles. Even with the arrival of the Abrams, the M60’s life was not over. It continued to serve in armies around the world, some of whom (for example, the Israelis) made improvements of their own. Over 15,000 were produced in total, and Turkey and Egypt remain major operators of the type to this day.