In pictures: The Vietnam War

The plan failed. Despite a peak of over 500,000 US troops in the country, by 1973 the US halted offensive operations and later in the year withdrew all combat troops, ending the longest war in its history.

Military advisers remained for a further two years as the Republic of South Vietnam fought on. Finally on 30 April 1975 North Vietnamese tanks entered the presidential palace in Saigon, bringing the war to an end.