The Soviet Union launched the Almaz program as a direct countermeasure to American Manned Orbiting Laboratory plans. Vladimir Chelomey led OKB-52 design bureau to create this secret initiative featuring armed military stations. The program included a 23mm Rikhter cannon for defense measures and aimed to compete with U.S. Air Force MOL projects.
The first Almaz station launched on the 3rd of April 1973 under the designation Salyut 2. An accident days after launch left the vessel disabled and depressurized before any crew could arrive. This failure marked the beginning of a series that would eventually include three operational units.
Three crews total operated Almaz stations for eighty-one days combined before program termination. Five crewed Soyuz expeditions flew to these military stations overall while only three missions actually reached their targets. Two of those missions were considered fully successful at that time.
Engineers reconfigured Almaz stations into uncrewed heavy radar-carrying reconnaissance satellites following cancellation. Three such satellites launched between November 1986 and March 1991 under various designations including Kosmos 1870. These spacecraft provided radar imagery with resolution down to twenty-five meters until deorbiting over the Pacific Ocean or other locations.
DOS space station core modules derived directly from the Almaz-OPS hull design mated with Soyuz-derived subsystems by Sergei Korolev's organization OKB-1. DOS-5 and DOS-6 served as cores for long-lived Salyut 6 and Salyut 7 stations respectively while DOS-7 provided the Mir Core Module. DOS-8 became the Zvezda Service Module still in use today on the International Space Station.