stabilization instrument malfunction. The second test was on February 5, 1966 and was also a failure due to a retrorocket issue. The third test took place on March 16, 1966. Nitrogen tetroxide spilled over the surface pad during fueling due to a miscommunication and the missile was quickly destroyed by fire. Some success was had with the fourth test on May 20, 1966, but the payload didn't break away from the missile's guidance system as intended. The following tests were conducted from silos. The first two tests of the silo phase ended in the intentional destruction (via self-destruct functionality) of the R-36O as a result of the second stage engine accidentally being activated for too long, sending the payload into an unplanned orbit. NATO radar systems picked up on the large mass of resulting debris. In one failed test case, small pieces of the missile rained down on the midwestern United States. In 1967, the Soviet Union conducted ten more R-36O tests, nine of them seeing some level of success. In that year and beyond, the Soviet Union used public statements about satellite launch tests as cover for any R-36O test that was intended to put its payload into orbit for some period of time. On November 19, 1968, about a month after the 20th test, the Soviet Union designated the R-36O as operational and began its deployment in three groups of six. By 1971, all 18 of the Soviet Union's R-36O silos were in service in Kazakhstan. NATO intelligence suggests that a primary target was the US Grand Forks Air Force Base where an ABM system was set to be established in the late 1960s to early 1970s. The R-36O wasn't equipped with a nuclear payload until 1972. Reasons for development The Soviet Union identified a number of strategic advantages of the FOBS. The following points prompted its development: The system granted unlimited striking range with a nuclear weapon. The system allowed a strike to be carried out from any direction. For instance, the Soviet Union could launch an attack against the United States using a South Pole or North Pole flight path; technically, it could even execute both of these attack plans simultaneously. The system provided a way of evading early warning radar systems. This advantage comes from two different attributes of the FOBS: (1) that it could attack from any direction, as stated above, and (2) that