For extraordinary heroism as a Platoon Leader of Company A, First Battalion, Twenty-fifth Marines, Fourth Marine Division, in action against enemy Japanese forces on Iwo Jima, Volcano Islands, 19 February 1945. Landing on D-day with the first wave of infantry, Second Lieutenant Shannon courageously led his platoon inland in the face of intense hostile mortar, rocket, artillery and small-arms fire. When his company’s right flank was held up by heavy machine-gun fire from an enemy pillbox, he advanced thirty yards ahead of his front line troops with two riflemen covering him and, after failing in an attempt to destroy the Japanese emplacement with hand grenades, courageously led a charge on the two riflemen. Although subjected to devastating hostile machine-gun fire from two mutually supporting enemy positions during the charge, Second Lieutenant Shannon continued on inside the position and, when his carbine jammed, clubbed the enemy manning the machine gun to death while his two comrades bayoneted the remaining troops. His bravery, initiative and aggressive fighting spirit throughout were in keeping with the highest traditions of the United States Naval Service.