In January 1963 regular army and civil guard forces of the Republic of Vietnam engaged a Viet Cong battalion at the village of Ap Bac in Dinh Tuong province, 35 miles southwest of Saigon in the Mekong Delta.
Unlike the Viet Cong, the South Vietnamese forces enjoyed a 4-1 numerical advantage and were supported by artillery, armor, and helicopters. Nevertheless, the Viet Cong battalion inflicted heavy casualties on the government forces and escaped with minor losses. Three American advisers were killed in the fighting and five helicopters were shot down.
Source: Battle of Ap Bac 1963