The 278th Armored Cavalry Regiment (278th ACR, "Third Tennessee"), previously the 117th Infantry Regiment, is an armored brigade combat team of the Tennessee Army National Guard with headquarters in Knoxville, Tennessee. It is the only National Guard Armored Cavalry Regiment and one of only two in the entire US Army order of battle, the other being the active duty 11th ACR. The unit traces its lineage from the volunteer militias of Eastern Tennessee and has participated in conflicts from the Revolutionary War to the Global War on Terror.