Fractional Orbital Bombardment System

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Fractional Orbital Bombardment System (FOBS) was a Soviet ICBM program in the 1960s that after launch would go into a low Earth orbit and would then 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 Outer Space Treaty banned nuclear weapons or weapons of mass destruction in earth orbit. However, it did not ban systems that were capable of placing weapons in orbit, and the Soviet Union avoided violating the treaty by conducting tests of its FOBS system without live warheads.

The Soviets developed three missiles to employ FOBS, with only one entering service:

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 Global Rocket 1, or GR-1, was cancelled due to engine problems.
The R-46 was not developed, and eventually scrapped.

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:

(...)

(c) systems for placing into Earth orbit nuclear weapons or any other kind of weapons of mass destruction, including fractional orbital missiles;

The missile was phased out in January 1983 in compliance with this treaty.