During World War II, Krulewitch held the rank of lieutenant colonel and served with the 4th Marine Division in the Asiatic-Pacific Theater. Between 1942 and 1944, his unit saw action at the battles of Tulagi and Gavutu–Tanambogo, Saipan, Tinian and Roi-Namur Island. In March 1945, during the Battle of Iwo Jima, Krulewitch commanded the 4th Provisional Battalion, which was responsible for attacking bypassed Japanese positions.