US President Dwight Eisenhower authorized a Central Intelligence Agency (CIA) operation to overthrow Árbenz, code-named Operation PBSuccess in August 1953. Within the CIA, the operation was headed by Frank Wisner, who had worked in the US intelligence services since World War II. While preparations for Operation PBSuccess were underway, the US government issued a series of statements denouncing the Guatemalan government, alleging that it had been infiltrated by communists. On June 18, 1954 Carlos Castillo Armas, a Guatemalan army Colonel in exile since a failed coup in 1949, led an invasion force of 480 men into Guatemala. The invasion was supported by a campaign of psychological warfare, which presented Castillo Armas's victory as a "fait accompli" to the Guatemalan people. Worried by the possibility of a US invasion, the Guatemalan army refused to fight, and on June 27 Árbenz resigned.