FAS
In the early 1960s, the Soviets needed a way to overcome the West's geographic advantages (forward bases in Turkey, Europe, and Asia from which shorter range missiles and bombers could attack the USSR). The Soviet attempt to place missiles in Cuba would have been a partial remedy. When the Cuban venture did not go as planned, they moved to other technological possibilities. The Soviets demonstrated the technology necessary to orbit a space vehicle and then land it in a specific place with the Vostok launches. It was thus logical to assume they could place nuclear weapons in orbit and return them to Earth at any time and place. Khrushchev made this suggestion in 1961, but on 15 March 1962, as part of the rhetoric proceeding the Cuban crisis, he made yet another, more ominous suggestion.
We can launch missiles not only over the North Pole, but in the opposite direction, too. . . . Global rockets can fly from the oceans or other directions where warning facilities cannot be installed. Given global missiles, the warning system in general has lost its importance. Global missiles cannot be spotted in time to prepare any measures against them.
This statement was the first hint of a new concept called the fractional orbit bombardment system (FOBS).
The 1961 Global Rocket 1 (GR-1) requirement chartered a competition for the development of a Fractional Orbital Bombardment System. Yangel offered the R-36O. Korolev proposed the 8K713, which was cancelled in 1964 prior to flight testing due to engine delays. Chelomei proposed the UR-200, which was cancelled following the October 1964 ouster of downfall of Khrushchev, who had been Chelomey's political patron.
The R-36O SS-9 Mod 3 SCARP with a modified upper stage was equipped with an orbital nose cone, which contained an instrumentation section, a single-chambered liquid propellant retrorocket motor and a nuclear warhead. The orbital missile carried a one- to three-megaton warhead according to Western estimates [and five megatons according to some published Russian estimates -- about the only instance in which published Russian yield estimates are higher than published Western estimates]. Flying into low-Earth orbit gave the ICBM unlimited range and allowing it to approach the US from any direction, avoiding US northern-looking detection radars and, therefore, giving little or no warning. The reentry vehicle came down in less than one revolution, hence the "fractional" orbit.
After the failure of their first two tests in 1966, the Soviets tested their FOBS with nine launches between 25 January and 28 October 1967. All missions followed the same distinct flight profile--launching in the late afternoon into an elliptical, near-polar low-Earth orbit and deorbiting over the Soviet landmass before one complete orbit. This profile allowed the Soviets to monitor the deorbit, reentry, and impact. US planners viewed FOBS as a pathfinder system intended to precede a conventional ICBM attack. The FOBS would circumvent the existing US ballistic missile early warning radars and hit SAC airfields before the bombers could take off. FOBS could destroy ABM radars, disrupt US retaliatory capability, destroy command posts, the White House, and the command and control network. But, due to its limited accuracy and payload, FOBS was ineffective against hardened targets.
Under the 1967 Outer Space Treaty, the Soviets could orbit everything but the nuclear warhead. Some US Senators were concerned with the Soviet FOBS development which followed on ratification of the Outer Space Treaty. The Soviets could, without treaty violation, deploy the weapons system minus the warheads.
By 1968 the Soviets' FOBS program settled into a two-flight-per-year pattern which indicated an operational status, although they only deployed FOBS in 18 silos. Little attention was paid to these events in the United States, because they occurred during the national election and at a time when Vietnam had all the headlines. At that time it remained unclear to US intelligence whether the Soviets were developing FOBS, or ballistic missiles with depressed trajectories and deboost capabilities.
The orbital missile 8K69 was initially deployed on 19 November 1968, and the first regiment with the R-36 orbital missiles was put on alert on 25 August 1969. The orbital missile was phased out in January 1983 in compliance with the SALT-2 treaty, which prohibited the deployment of these missiles.
https://fas.org/nuke/guide/russia/icbm/r-36o.htm
