The concept for the M60 began at the end of World War Two, when US Ordnance officers became very interested in the German concept of a universal machine gun (originally conceived by the Danes, but first put into large-scale use by the Germans). This was the idea of having a single machine gun that was suitable for use as a light MG by a single man or 2-man team off a bipod, or as a heavy MG run by a full crew off a stable and sophisticated tripod, or as a vehicular or antiaircraft MG with other types of mounts. Up to this point, the US machine gun service was divided between static tripod-mounted guns (M1919A4/M1917A1) and automatic rifles (M1918A2). The one major US attempt at a light MG (not counting the Johnson) was the M1919A6 and it was a quite awkward kludge of a gun.
Initially, the first concept for the M60 was essentially a second model FG-42 with an MG-42 feed system shoehorned onto it. The first prototypes were made by the Bridgeport Tool & Die Company, with Springfield Armory stepping in to assist in 1947. The gas system that was chosen for the gun was a gas expansion and cutoff type, similar to the M14 gas system. At any rate, Bridgeport had a contract to develop the design, but actual production was contracted to Inland, with the first 100 guns batch made in 1951. The first field testing was done in 1953, and it was adopted into service in 1957.