The Commandant's Office in the Washington Navy Yard, also known as Building One, Quarters J, or the Middendorf Building is the U.S. Navy's oldest active office building, which historically housed the offices of the Commandant and other officers of the Washington Navy Yard in Washington, D.C. It sits at the south end of Dahlgren Avenue, the Yard's main road, two blocks south of the Latrobe Gate near the Anacostia River. After renovation in 1993, it became offices for the Naval Historical Center. Since 2005, the building has been restored to its historical use as office of the Commandant. It was likely built from 1837 to 1838 and first appears on a map of the yard in 1842. In 1973 it was listed on the National Register of Historic Places.