U.S. Special Forces members advise South Vietnamese soldiers and local militia troops on patrol near Cambodia in November 1969 
as they fight the Viet Cong insurgency. U.S. commanders had to develop not only a counterinsurgency plan for guerrilla forces but also a strategy for battling the conventional forces of the North Vietnamese Army. (David Turnley/Corbis via Getty Images)

David Turnley/Corbis via Getty Images