The increasing tempo and scope of the Vietnam War brought "O'Hare" an assignment to WestPac duty. Steaming from Norfolk, on 1 June 1966, she assumed station as a gun support ship along the coast of Vietnam on 15 July, firing missions in all four Corps areas in the South. "O'Hare" served as plane guard for aircraft carriers on "Yankee Station" in the Gulf of Tonkin, participated in "Sea Dragon" operations, patrolled on search and rescue duties off North Vietnam. "O'Hare" returned home on 17 December via the Suez Canal, completing a circumnavigation of the world. In March 1968, along with from Mayport, "O'Hare" deployed to the Indian Ocean via Africa and made 17 port calls in the Middle East. In January 1969 with Destroyer Squadron 32 (DesRon 32) she again deployed to the Mediterranean.