On March 16, 1967, Mendez was conducting a Search and destroy mission with his company when they came under attack from a Viet Cong battalion. Half of his platoon was pinned down in a rice paddy under enemy fire, and Mendez volunteered to lead a squad to assist the pinned-down Marines in returning to friendly lines with their two dead and two seriously wounded men. Mendez exposed himself while returning fire with his M79 grenade launcher on the enemy. His Platoon Commander, Lieutenant Ronald D. Castille was seriously wounded and he fell, unable to move. Using his own body, Mendez shielded Lt. Castille as he applied a dressing to the wound, he then picked up the Lieutenant and started to carry him to friendly lines, which were more than seventy-five meters away. Mendez was hit in the shoulder and two of his comrades rushed to help him with their commander, Mendez however refused to let go of his platoon commander and chose to act as rear man. Mendez continued to shield his lieutenant with his own body until he was mortally wounded. Mendez was posthumously awarded the Navy Cross and promoted to sergeant.