McMaster commanded troops in both American wars in Iraq — in 1991, when he fought in a storied tank battle known as the Battle for 73 Easting, and again in 2005-2006 in one of the most violent periods of the insurgency that developed after the U.S.-led invasion in 2003. He is credited with using innovative approaches to countering the insurgency in the northern Iraqi city of Tal Afar when he commanded the 3rd Armored Cavalry Regiment. He later served as a special adviser to the top U.S. commander in Iraq.