Soviet tests of a fractional orbital bombardment system (FOBS) attracted the interest of the US intelligence community because of the unique challenges it posed to defenses. At that point, August 1967, the US had no means to detect a FOBs attack but INR noted that a satellite detection system would be operational during 1970. This was a reference to the secret Defense Support Program (DSP), which would use infrared technology to detect missile launches and reduce any surprise advantage from the FOBs. The Soviets recognized this and later retired their twenty or so ICBMs with FOBs capabilities in 1983.
