By 1910, the area including Belvoir was sold to the US Government. In 1912, the land was transferred to the War Department, designated for use as an Army training site, and was first used in 1915. By 1918, the area was transformed into Camp A.A. Humphreys. Training exercises at the camp included rifle practice, trench warfare, and floating or "ponton" bridge building.
After World War I, Camp Humphreys retained a small garrison and expanded from its original 1,500 acres to 6,000 in 1919. In 1922, the Camp was renamed Fort Humphreys, a permanent post. In 1935, the post was renamed Fort Belvoir, and expansion efforts began. By the end of World War II in 1945, almost 150,000 engineer troops had been trained at Fort Belvoir. Since that time, Fort Belvoir has provided many vital services to the Nation. Today Fort Belvoir serves the National Capital Region as an Administrative Support Center.
In 1931, Colonel Edward H. Schulz, Commanding Officer, began the first archaeological investigation at Belvoir. In the 1970s Captain George Shott, Jr. undertook a four year archaeological investigation, supported by the US Army Engineer Museum, in partnership with Fairfax County Public Schools. The project resulted in listing the Belvoir Ruins and Fairfax Family Gravesite in the National Register of Historic Places in June 1973. Since that time, there have been other archaeological investigations of the Belvoir site, yes there is still much to be learned about life in the 18th century and the Fairfax family.
The Army has been a steward for this important site by providing for research, preservation and interpretation.