OPS-4 is an unflown Soviet space station, expected to be a fourth in the secret Almaz military program. It was initially planned for launch in late 1977, but delays in readiness of the TKS spacecraft caused this date to be shifted. By December 1978 cosmonauts were training for OPS-4 with an estimated launch date of December 1980, but the Almaz program was formally cancelled in February 1979.[1][2]