The M1A1 Abrams main battle tank is the principal combat tank of the United States Army. The M1 Abrams was designed by the General Dynamics Corporation and first entered US Army service in 1980. An improved version of the M1, the M1A1 was introduced in 1985. The M1A1 has a 120mm smoothbore gun developed by Rheinmetall GmbH of Germany, improved armor and an NBC protection system. Further combat was seen during 2003 when US forces invaded Iraq and deposed the Iraqi leader Sadddam Hussein. No Abrams tank has ever been destroyed as a result of fire from an enemy tank, though a number have been disabled in ambushes employing short-range antitank rockets like the Russian RPG7 and RPG18.