it could travel along a very low Earth orbital path. The first point has to do with the fact that one of the primary missile defense radar systems of the US around the time of the FOBS' early development was the Ballistic Missile Early Warning System (BMEWS). The BMEWS was oriented to detect ballistic missiles coming from the aforementioned 'North Pole route' (its three stations being located in Alaska, Greenland, and the United Kingdom) and therefore wouldn't detect a strike flying along a southern orbital path. The second point considers that FOBS missiles could fly relatively close to the Earth's surface; they could have a perigee of under 100 miles (160 km) and an apogee as low as 125 miles (200 km) above the ground (see apsis). US radar systems like the BMEWS were configured to detect ICBMs that flew several hundred to upwards of 1000 miles (1600 km) above the surface, not low altitude missiles like that of the FOBS. Thus, the Soviet Union felt that striking with a FOBS would deprive the United States of valuable warning time that ICBMs were likely to give away, time that could be used to mount a devastating retaliatory attack. The system concealed the target location until the payload was dropped out of orbit. Theoretically, the FOBS was capable of staying in orbit for several orbits, at most, due to the exceptionally low trajectory, but could separate its warhead from the FOBS vehicle at any given point in the orbit. The FOBS' flight duration was shorter than that of an ICBM (assuming an indirect route isn't taken for the purpose of radar evasion). A FOBS missile may have been able to reach its target around 10 minutes before an ICBM would. The Soviet Union supposed that the FOBS would be capable of trumping US anti-ballistic missile (ABM) systems. This was actually a primary objective of the Soviet FOBS from its origin. On one hand, the FOBS was seen as a tool that could boost the effectiveness of a Soviet ICBM strike by first eliminating some of the enemy's safeguards (like ABM systems). Given the notion that a FOBS missile could not be destroyed by an ABM system, it also follows that the FOBS could be used alone to carry out a nuclear attack. In late 1967, US officials indicated that they could develop ABMs to counter the Soviet FOBS, the implication being