The M1 Abrams entered U.S. service in 1980, replacing the 105 mm gun, full tracked M60 Patton main battle tank. It did, however, serve for over a decade alongside the improved M60A3, which had entered service in 1978. Three main versions of the M1 Abrams have been deployed, the M1, M1A1, and M1A2, incorporating improved armament, protection and electronics. These improvements, as well as periodic upgrades to older tanks have allowed this long-serving vehicle to remain in front-line service. The M1A3 is currently under development. It is the principal main battle tank of the United States Army and Marine Corps, and the armies of Egypt, Kuwait, Saudi Arabia, Australia, and in 2010 Iraq. The M1 Abrams is anticipated to be in U.S. service until the 2050s, approximately 70 years after entering U.S. service.