Operation Buffalo ended in South Vietnam after 12 days of fighting that left 159 U.S. Marines killed .
345 wounded for the U.S. Marines ' heaviest losses during the Vietnam War ; the U.S. Marines reported that 1,290 of the enemy had been killed .
Operation Buffalo ended in South Vietnam after 12 days of fighting that left 159 U.S. Marines killed and 345 wounded for the Marines ' heaviest losses during the Vietnam War ; the Marines reported that 1,290 of the enemy had been killed .