According to Wikipedia: "The M60A2 was intended as a stop-gap solution until the projected replacement by the MBT-70. The M60A2, nicknamed the "Starship" due to its Space Age technology, featured an entirely new low-profile turret with a commander's machine-gun cupola on top, giving the commander a good view and field of fire while under armor but spoiling the low profile. It featured a 152 mm (6.0 in) main gun similar to that of the M551 Sheridan light tank, which fired conventional rounds as well as the MGM-51 Shillelagh anti-tank missile system. The fitting of a CBSS (closed breech scavenger system), which used pressurized air to clear the breech after each shot, solved the problem of unburnt propellant from the main gun rounds fouling the barrel and pre-detonating subsequent rounds. The M60A2 proved a disappointment, though technical advancements would pave the way for future tanks; the MBT-70, which relied on much of this technology as it was used in the M60A2, never advanced beyond prototype stage though. The Shillelagh/M60A2 system was phased out from active units by 1981, and the turrets scrapped. Most of the M60A2 tanks were rebuilt as M60A3, or the hulls converted to armored vehicle-launched bridge (AVLB) vehicles."