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Impact on the U.S. military

More than 3 million Americans served in the war, 1.5 million of whom saw combat. James Westheider wrote that "At the height of American involvement in 1968, for example, 543,000 American military personnel were stationed in Vietnam, but only 80,000 were considered combat troops." Conscription in the US existed since World War II, but ended in 1973.

58,220 American soldiers were killed, more than 150,000 wounded, and at least 21,000 permanently disabled. The average age of US troops killed was 23. According to Dale Kueter, "Of those killed in combat, 86% were white, 13% were black..." Approximately 830,000 veterans, 15%, suffered posttraumatic stress disorder. This unprecedented number was because the military had routinely provided heavy psychoactive drugs to servicemen, which left them unable to process trauma. Drug use, racial tensions, and the growing incidence of fragging—attempting to kill unpopular officers with grenades or other weapons—created problems for the military and impacted its capability to undertake operations. 125,000 Americans left for Canada to avoid the draft, and approximately 50,000 servicemen deserted. In 1977, President Jimmy Carter granted an unconditional pardon to all Vietnam-era draft evaders with Proclamation 4483.

The war called into question army doctrine. Marine general Victor H. Krulak criticized Westmoreland's attrition strategy, calling it "wasteful of American lives... with small likelihood of a successful outcome." Doubts surfaced about the ability of the military to train foreign forces. There was found to be considerable flaws and dishonesty by commanders, due to promotions being tied to the body count system touted by Westmoreland and McNamara. Secretary of Defense McNamara wrote to President Johnson his doubts: "The picture of the world's greatest superpower killing or seriously injuring 1,000 noncombatants a week, while trying to pound a tiny backward nation into submission on an issue whose merits are hotly disputed, is not a pretty one."