Built by Philadelphia contractor John McShain, the building was dedicated on January 15, 1943. It is the highest-capacity office building in the world and one of the world's largest buildings in terms of floor area. It houses approximately 23,000 military and civilian employees and about 3,000 non-defense support personnel. It has five sides, five floors above ground (plus two basement levels), and five ring corridors per floor with a total of 17.5 miles (28 km) of corridors.