 Camp Rapid developed as a summer encampment site for the South Dakota National Guard in the early 20th century, using land borrowed from the Bureau of Indian Affairs "Sioux Sanitorium" and Rapid City Indian School, today's Indian Health Service (IHS) SiouxSan Hospital, located just west of Camp Rapid.It became a permanent installation during and immediately after World War I, when it was used for mobilization of National Guard units for the front in France.Its use continued during the 1920s and 1930s, and it was taken over as a federal installation during World War II.