The M1A1/2 Abrams main battle tank is manufactured by General Dynamics Land Systems (GDLS). 4,796 M1A1 tanks were built for the US Army. The main armament is the 120 mm M256 smoothbore gun, developed by Rheinmetall GmbH of Germany. The M1A1 tank incorporates steel encased depleted uranium armour. Armour bulkheads separate the crew compartment from the fuel tanks.The tank is protected against nuclear, biological and chemical (NBC) warfare.