The James V. Forrestal Building is a low-rise Brutalist office building located in Washington, D.C., in the United States. Originally known as Federal Office Building 5, and nicknamed the Little Pentagon, the Forrestal Building was constructed between 1965 and 1969 to accommodate United States armed forces personnel. It is named after James Forrestal, the first United States Secretary of Defense. It became the headquarters of the United States Department of Energy after that agency's creation in 1977.