To provide air defense of the base, the United States Army established the Ellsworth AFB Defense Area in 1957 and constructed Nike-Ajax Surface-to-air missile sites. Sites were located near Ellsworth AFB: E-01 was north , E-20 was east-northeast , E-40 was south-southeast , and E-70 was west-southwest . Headquarters facilities were located at Ellsworth. In 1958, batteries E-20, E-40, and E-70 were removed from service and E-01 was converted to fire Nike Hercules missiles. This battery remained in service until 1961. as part of the reduction of the air defenses in the United States against aircraft.