Short assignments in infantry units followed before the outbreak of World War II. Lieutenant Nihart then served as a gunnery officer on board the aircraft carrier USS "Saratoga" (CV-3), when it unsuccessfully tried to assist Wake Island immediately after Pearl Harbor in December 1941. That was followed by other shipboard and infantry-amphibious training assignments and schooling. He taught both U.S. Marine and Army units amphibious landing tactics. From April to June 1945, Major Nihart served as the executive officer of 1st Battalion, 1st Marines during the battle of Okinawa. Following that, he was assigned to the forces in North China.