On January 30, 1968, Vietcong units initiated attacks throughout I and II Corps, and by January 31, 1968, Vietcong and North Vietnamese soldiers were attacking American and South Vietnamese forces throughout the country. In addition to attacking thirty-six of forty-four provincial capitals and five of six major cities, the Vietcong attacked the U.S. embassy in Saigon, Tan Son Nhut Air Base, the presidential palace, and South Vietnam general staff headquarters. In the summer of 1967, the North Vietnamese began planning for the January 1968 offensive. They decided to launch diversionary raids in the Central Highlands and northern border areas, the most well-known of which was the months-long siege of United States Marines at Khe Sanh. The purpose of the raids was to mislead American intelligence, because during the campaigns in the highlands and northern provinces, Vietcong were gradually moving into the provincial capitals and major cities to prepare for the Tet assaults. While all this was going on, both the North Vietnamese and the National Liberation Front (Vietcong) called for a cease-fire during the Tet holiday celebrations. By the time of the holiday, they had moved 100,000 soldiers and considerable amounts of supplies undetected into the cities.
On two levels, the Tet Offensive was a tactical debacle for the Vietcong and North Vietnamese. The offensive had failed in that the South Vietnamese army had held and American troops, airlifted into the critical areas, swiftly regained control, except in Hue where the fighting continued for weeks. Nor had the South Vietnamese risen up in mass and rallied to the "Vietcong liberators." Lastly, the Vietcong and North Vietnamese may have suffered as many as 40,000 battlefield deaths, compared to 1,100 for the United States and 2,300 for the South Vietnamese. The Vietcong were so devastated by the fighting that they never regained their strength, and after the Tet Offensive the war in Vietnam was largely a struggle between mainline U.S., ARVN (Army of the Republic of Vietnam), and North Vietnamese regulars.
But if the Tet Offensive was a strategic defeat for the Vietcong and North Vietnamese, it was also a huge tactical victory. Throughout 1966 and 1967, American military and political leaders had been talking of the progress in the war, how the enemy would not long be able to prolong such massive losses, how there was a "light at the end of the tunnel," how the war would soon be over. The Tet Offensive, by exposing the resolve of the Vietcong and North Vietnamese, as well as their continuing vigor, demoralized American public opinion. Television reporters broadcast home the unbelievable sight of General William Westmoreland, standing beside several dead Vietcong inside the U.S. embassy compound, describing the American victory. The Tet Offensive led promptly to the defeat of President Lyndon B. Johnson in the New Hampshire Democratic primary and his withdrawal from the race in March 1968. After Tet, American policy toward Vietnam had little to do with winning the war, only with finding an "honorable" way out.