Although the South Vietnamese and American forces were taken by surprise by the massive surprise attacks by the Viet Cong forces, they were eventually able to contain them, inflicting massive casualties on the enemy troops. Nevertheless, the Tet Offensive that began on January 31, 1968 served notice to the United States that the North Vietnamese were capable of mounting a major strike backed by large numbers of troops.
The Tet Offensive was so named because it fell on the first day of the lunar new year (known as Tet Nguyen Dan)--Vietnam's most important holiday. The North Vietnamese initially gained the momentum since both sides had previously agreed to a two-day truce in honor of the holiday. The Viet Cong's first-day attacks struck in more than 100 locations utilizing at least 80,000 troops. American and South Vietnamese forces inflicted heavy losses (approximately 37,000 casualties) during the two months of the offensive's first phase. Tens of thousands of civilians were also killed or wounded.
The offensive, meant to disrupt South Vietnam and hopefully cause an uprising that would topple the Saigon government, involved the largest numbers of troops in the war up to that time. It was a strategic victory for South Vietnam and the U.S., but it also showed that the war was far from nearing its end.