Last week I wrote about some of the apparent differences between how the US and the Soviet Union used satellites for mapping and geodesy. The Soviets seem to have been slower to operate dedicated satellites in both areas, with no apparent explanation. Though it’s dubious to use US intelligence estimates as evidence of what the Soviets were actually doing, they do at least shed light on some of the possibilities.
Two CIA reports from from the pre-sattellite era, in 1954 and 1957, suggested that if the Soviets had made a connection across the Bering Strait between their own domestic surveys and the North American Datum, missiles launched from near the Bering Strait would have a Circular Error Probable (CEP) of 300–500 feet. Without the connection between datum, the error would be closer to 1,000 feet. By making observations of an upcoming solar eclipse and gaining access to the equivalent measurements from US or Western European sites, the CIA predicted the error in intercontinental position could be reduced to about 500 feet from anywhere in the Soviet Union.
These estimates assumed that the target could be located on high-quality American maps, which the analysts presumed were available to Soviet planners. But what if the targets were secret sites not plotted on any maps? A Studies in Intelligence article (“Spy Mission to Montana”) from 1995 revealed that the CIA and Air Force tested those conditions as the silos for Minutemen ICBMs were being built in 1962. A three-person team, two from the CIA and one from the Army Map Service, made covert observations of the sites under construction from their rental car. Dodging both site security and the official survey being done by the Air Force’s 1381st Geodetic Survey Squadron, the covert team proved that observations could be made with a CEP of 600 feet when maps at 1:250,000 scale were available and a CEP of 200 feet with 1:62,500 scale maps.
Did the Soviet Union make a secret measurement of the Bering Strait or send its agents to survey the locations on American missile silos? The answer is probably somewhere in the files of the KGB or GRU.