Introduced in 1957, until recently it remained in use in every branch of the U.S military and still serves in other armed forces. Its manufacture and continued upgrade for military and commercial purchase continues into the 21st century though it has been replaced or supplemented in most roles by other designs, notably the M240 (U.S. Forces' nomenclature for the FN MAG-58) in U.S service.
Frank Jackson, a Vietnam War veteran, stole an M-60 during his service and buried it in the woods behind his house along with three 7.62 mm ammunition boxes. He justified it, at least to himself, by saying that the Army "owed" him.
After the Ring of Fire, Jackson unearthed his illegal weapon and revealed it to Mike Stearns and Dan Frost, effectively donating the machine gun to Grantville's army. The M-60 was used at the Battle of the Crapper, where it helped rout the mercenary band attacking Badenburg. While it did not account for most of the casualties, it had a strong psychological effect, especially since the day was overcast and one in five rounds was a tracer.