On Order, A Company, 1st Battalion, 3d US Infantry Regiment, deploys by land or air to: Assist with NBC operations, conduct area security operations, and control civil disturbances in support of the Military District of Washington’s defense to the National Capital Region. Alpha Company also conducts Joint and Army ceremonies and funerals in support of the Military District of Washington.

Company A is stationed and billeted on Fort Lesley J. McNair, in the city limits of the District of Columbia. It is historically known as the Commander-in-Chief’s Guard and is patterned after General George Washington’s personal guard of that day. It conducts tactical training year round to sustain proficiency in its Rifle Company's tasks that support the 3d U.S. Infantry Regiment's (The Old Guard) mission to defend the Nation Capital Region. Along with its standard Riffle Company mission requirements, this unit also maintains ceremonial and tactical proficiency in the weaponry and tactics of the 18th century. This CinC Guard function is performed in many Department of Defense and Department of the Army ceremonies year round. In addition to their CinC Guard functions, Alpha Company also conducts memorial affairs in Arlington National Cemetery.