Castle Air Force Base is a former United States Air Force Strategic Air Command base in California, northeast of Atwater, northwest of Merced, and about 115 miles south of Sacramento. The Central Valley base in unincorporated Merced County was closed in 1995, pursuant to a Base Realignment and Closure Commission decision after the end of the C…Castle Air Force Base is a former United States Air Force Strategic Air Command base in California, northeast of Atwater, northwest of Merced, and about 115 miles south of Sacramento. The Central Valley base in unincorporated Merced County was closed in 1995, pursuant to a Base Realignment and Closure Commission decision after the end of the Cold War and the disestablishment of Strategic Air Command. It is now known as the Castle Airport Aviation and Development Center.