Answer:
Between 1959 and 1962, Sheehan fought as an army officer during the war with Korea, in the 7th Infantry Division, whose newspaper he also directed. He was then sent to the Tokyo barracks, where he edited Bayonet magazine. There he began his career as a correspondent for the news agency United Press International (UPI), which entrusted him with the mission of serving in Vietnam. In 1964, for his extraordinary work, the Times recruited him to be one more season in the main theater of operations of the Indochina war.
Sheehan along with David Halberstam and Malcolm Browne were among the trio of most eminent and respected war correspondents in Vietnam. The three of them used to report on the course of the conflict in a different way than the official communiqués reproduced by the press that responded to the dictates of Nixon.