tet offensive
The Tet Offensive was a massive series of attacks by the National Liberation Front and People's Army of Vietnam against the forces of the Army of the Republic of Vietnam and their international allies. It was the largest escalation of the Vietnam War to date, and was timed to coincide with (and thus named for) the traditional Vietnamese Tet lunar new year at the end of January, 1968. In the early morning of 30 January 1968, attacks began against hundreds of towns and cities all across South Vietnam.
The Tet Offensive was a catastrophic military failure. Contrary to communist expectations, ARVN forces fought fiercely and repelled most of the attacks on their own, and South Vietnam's international allies were able to redeploy to assist faster than the North Vietnamese expected. The NLF engaged in open warfare for the first time since 1965 and were all but wiped out. Despite brutal fighting in the capital Saigon and city of Hue, the Tet Offensive was unable to accomplish any of their military goals.
This fate was opposite, however, in the political sphere. The American public had been told by their leaders for months that the North Vietnamese were on the edge of defeat and incapable of launching an offensive of any kind. Public trust in their leader's ability to prosecute the war plummeted. As opposed to the Battle of Hamburger Hill, which entered public consciousness for its seeming waste, Tet is known in public consciousness as the point when Western governments could no longer deny that they were losing in Vietnam.