The career Marine non-commissioned officer was killed in Vietnam a week before he would have completed 20 years of military service and become eligible for retirement. MacKenna had been in the war-torn country more than a year, but instead of returning to the United States, he extended his tour with Company E of the 2nd Battalion, 1st Marines, 1st Marine Division, and remained in Vietnam. The gunnery sergeant died on May 29, 1966, near the village of Phu Bai in Thua Thien Province. He was posthumously awarded the Silver Star. MacKenna had attended St. Thomas More High School. He enlisted in the Army in 1946, when he was 17 years old, and then enlisted in the Air Force a year later, After another year of service, MacKenna enlisted in the Marine Corps and served with the Marines during the Korean War. He was survived by his father, brother and sister.