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. Wikipedia