OPS-4 was an unflown Soviet space station, expected to be a fourth in the secret Almaz military program. It remained grounded due to the cancellation of the program.
Spacecraft
OPS-4 underwent several technical and design changes. The aft docking port was designed to receive heavier TKS spacecraft, compared to a lighter Soyuz-enabled docking port in the three previous stations.
It was to be the first station launched with a three panel Mech-A Synthetic Aperture Radar and a manned reusable Return Vehicle VA. The VA was replaced by a second docking port, due to delays in preparing a crew-rated TKS; the front section was refitted with a Soyuz-enabled docking port to receive manned craft.
OPS-4 was to carry an advanced Shchit-2 space-to-space cannon. It was reported to be a two projectile system armed with unguided missiles.