World War II broke out during Jack Williams's first year of college at the University of Illinois. He decided to join the U.S. Navy and trained at the Great Lakes Naval Air Base as a gunner. Williams served in the Pacific theater from 1944 to 1945, and was assigned to the U.S.S. Petrof Bay (CVE 80), an escort carrier. Williams served as a gunner in a Grumman TBF Avenger, a carrier based torpedo bomber. The ship saw action in the Battle of Leyte Gulf, and at both Iwo Jima and Okinawa.