Nuclear missile silo test site. Aerial photograph of a site used to test hardening of nuclear missile silos. This site is used to test whether US nuclear missiles (fired from underground silos) would survive an attack intended to destroy them. The missiles (intercontinental ballistic missiles, ICBMs) are some distance below the surface, protected by blast doors. The silos are heavily reinforced-steel and concrete underground structures that would be hardened to withstand huge blast pressures. Super-hardening made them even tougher. This site is near Yuma, Arizona, USA. Photographed on 21 June 1986.