Tet Offensive (January–February 1968) - a major communist offensive involving both North Vietnamese Army (NVA) and Viet Cong forces against South Vietnamese (ARVN) and U.S. positions throughout South Vietnam. Although ultimately defeated, the communists achieved surprise and inflicted heavy casualties, particularly during the opening stages. The ferocity and scale of the attacks shocked U.S. and South Vietnamese leadership while undermining public support for the war in both countries. Tet marked a significant turning point in the conflict, as it highlighted the communists' resilience and illustrated that military victory would be elusive despite the vast expenditure of U.S. resources committed up to that point.