A Marine holds security during a route clearance drill as a part of Exercise Steel Knight at Marine Corps Air Ground Combat Center Twentynine Palms, California, Dec. 13, 2015. The Marine is with 1st Combat Engineer Battalion. During route clearance Marines use a variety of vehicles to search for improvised explosive devices, mines and other dangerous obstructions. Steel Knight is a 1st Marine Division led exercise, which enables the Marines and sailors to operate in a realistic environment to develop skill sets necessary to maintain a fully capable Marine Air Ground Task Force. - A Marine holds security during a route clearance drill as a part of Exercise Steel Knight at Marine Corps Air Ground Combat Center Twentynine Palms, California, Dec. 13, 2015. The Marine is with 1st Combat Engineer Battalion. During route clearance Marines use a variety of vehicles to search for improvised explosive devices, mines and other dangerous obstructions. Steel Knight is a 1st Marine Division led exercise, which enables the Marines and sailors to operate in a realistic environment to develop skill sets necessary to maintain a fully capable Marine Air Ground Task Force.