1955 when US Advisers arrive in Vietnam. 1961 when US Special Forces (Green Beret) arrive in Vietnam. 1965 when US Regulars arrive, and the air campaign against North Vietnam commences (Operation Rolling Thunder). The invasion (incursion) of Cambodia in 1970, under Nixon's orders. The invasion of Laos in 1971, under Nixon's orders. The "maximum effort" aerial bombing of North Vietnam in December 1972, dubbed the "Christmas Bombings", President Nixon's "Linebacker II", (He loved football).