 The second stage of its Proton rocket failed; DOS-2 never reached orbit and crashed into the Pacific Ocean.Salyut 2 (OPS-1) (; ) was launched on 4 April 1973.The space station was, despite its "Salyut 2" designation, slated to be the first military space station, part of the highly classified Almaz military space station program – the Salyut designation was chosen to conceal its true nature.