Fractional Orbital Bombardment System (FOBS) was a SovietICBM in the 1960s with a low Earth orbit that would de-orbit for an attack. It had no range limit and the orbital flight path would not reveal the target location.
This would allow a path to North America over the South Pole, hitting targets from the south, which is the opposite direction from which NORAD early warning systems are oriented.
The orbital missile 8K69 was initially deployed in 1968, and the first regiment with the R-36 orbital missiles was put on alert in 1969.
The U.S. Defense Support Program early warning satellites enabled the US to detect a FOBS launch.
The SALT II treaty (1979) prohibited the deployment of FOBS systems:
Each Party undertakes not to develop, test, or deploy: