In the incredibly overheated, paranoid environment of the Cold War, anything seemed possible. Senator Joe McCarthy saw Communists hiding in every broom closet, Julius and Ehtel Rosenberg were executed as spies -- although the evidence we have today suggests that Ethel, at least, wasn't guilty of anything of the sort -- and the Federal Bureau of Investigation launched COINTELPRO, a series of covert actions spying on and disrupting various political organizations, including civil rights leaders and Vietnam war protesters. In 1951, according to a recently declassified FBI file, the agency also became convinced that an atomic bomb built by the Soviet Union could be hiding somewhere in New York City, waiting to be detonated. After receiving a rather flimsy tip from an unnamed informant in Brazil, the FBI spent several years quietly looking for the bomb.
Image via Wikimedia Commons Fat Man, the atomic bomb detonated over Nagasaki by the United States in 1945.