According to lasdontrailofhonor.com:
The Vietnam War was fought from 1959 to 1975, during a time of major social revolution and chaos on the home front. The war was another attempt to prevent Russia’s influence from spreading into Asia. North Vietnam was attempting to claim South Vietnam, similar to what happened in Korea, and Americans felt that the war would be a swift victory.
However, the North Vietnamese used guerilla warfare to strike at American troops patrolling through their native jungles. After years of fighting on the war front and rallies and protests on the home front, President Nixon pulled out U.S. troops in 1975. The monument shows a machine gunner in a worn uniform, reflecting the exhaustion of the servicemen who fought in Vietnam.