After joining the Army in 1942, Corso served in Army Intelligence in Europe. In 1945, Corso arranged for the safe passage of 10,000 Jewish World War II refugees out of Rome to the British Mandate of Palestine.
During the Korean War (1950-1953), Corso performed intelligence duties under General Douglas MacArthur as Chief of the Special Projects branch of the Intelligence Division, Far East Command. One of his primary duties was to keep track of enemy prisoner of war (POW) camps inNorth Korea. Corso was in charge of investigating the estimated number of U.S. and other United Nations POWs held at each camp and their treatment. At later hearings of the Senate Select Committee on POW/MIA Affairs, Corso provided testimony that many hundreds of American POW's were abandoned at these camps.
Corso was on the staff of President Eisenhower's National Security Council for four years (1953-1957). In 1961, he became Chief of the Pentagon's Foreign Technology desk in Army Research and Development, working under Lt. Gen. Arthur Trudeau. When he left military intelligence in 1963, Corso became a key aide to Senator Strom Thurmond. In 1964, Corso was assigned to Warren Commission member Senator Richard Russell Jr. as an investigator into the assassination of John F. Kennedy.
Corso relates in his book The Day After Roswell (co-author William J. Birnes) how he stewarded extraterrestrial artifacts recovered from a crash at Roswell, New Mexico, in 1947. According to Corso, the reverse engineering of these artifacts indirectly led to the development of accelerated particle beam devices, fiber optics, lasers, integrated circuit chips and Kevlar material.
In 1947, according to Corso, a covert government group (see Majestic 12) was assembled under the leadership of the first Director of Central Intelligence, Adm. Roscoe H. Hillenkoetter. Among its tasks was to collect all information on extraterrestrial spacecraft. The US administration simultaneously discounted the existence of flying saucers in the eyes of the public, Corso says.
Corso further relates that the Strategic Defense Initiative (SDI), or "Star Wars", was meant to achieve the capability of killing the electronic guidance systems of incoming enemy warheads and disabling enemy spacecraft, including those of extraterrestrial origin. Many of the claims made in this book have been challenged by other UFO researchers; for a detailed investigation of his claims, see Kal K. Korff's book The Roswell UFO Crash: What They Don't Want You to Know.