In early 1960, nuclear arms and power were not particularly high on the list of public concerns for Americans. The growing horror of the American public over fallout — a fear perhaps more real than the fear of nuclear war — quickly manifested itself in a series of protests symbolic of the 1960s. On May 1,1960, US Air Force pilot Francis Gary Powers floated across the sky, about 68,000 feet over the Soviet city of Sverdlovsk. As Soviet and American explosions continued into 1962, concerns rose. The dangers of underground testing reached their most critical point on December 18,1970, with the Baneberry explosion at the Nevada test site, 800 feet below the surface. The eventual withdrawal of US troops from Vietnam and the 1975 takeover by communists further divided and embittered Americans about the Vietnam experience. The early 1970s may be seen as the high water mark of the American nuclear program.