The M60 (formally named United States Machine Gun, Caliber 7.62 mm, M60) is a family of American general purpose machine guns firing 7.62x51mm NATO cartridges from a disintegrating belt of M13 links. There are several types of live ammunition approved for use in the M60, including ball, tracer, and armor-piercing rounds. The M60 was referred to as "The Pig" during the Vietnam War.  Introduced in 1957, it has served with every branch of the U.S. military and still serves with 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 in U.S. service.