Camp Callan was built in November of 1940 as a Coast Artillery Corps replacement training center for new inductees. Open for business in January of 1941, it was named for Maj. Gen. Robert Callan (1874-1936), a veteran of the Spanish American War and World War I.

Camp Grant was opened just south of Rockford in 1917 to train soldiers for World War I. It was closed in 1921 and turned over to the Illinois National Guard for use as a training center in 1924.

Camp Roberts, California  officially began it mission as a replacement training center in March 1941. At that time it ranked with the world's largest military training facilities. It may still be so in terms of training capacity, and so far as it is known features the largest parade ground (the length of fourteen football fields) on any military facility.