The militarisation of space involves the placement and development of weaponry and military technology in outer space. The early exploration of space in the mid-20th century had, in part, a military motivation, as the United States and the Soviet Union used it as an opportunity to demonstrate ballistic-missile technology and other technologies having the potential for military application. Outer space has since been used as an operating location for military spacecraft such as imaging and communications satellites, and some ballistic missiles pass through outer space during their flight.