Upon graduation in 1954, he received his commission in the U.S. Marine Corps through the Naval Reserve Officer Training Corps (Navy ROTC) on August 9, 1954, and subsequently reported to The Basic School at Marine Corps Base Quantico, Virginia, and after completing it, he was sent to NAS Pensacola, Florida, for flight training. He became a naval aviator in August 1956, and served with operational tactical jet squadrons of the Fleet Marine Force. He then attended the U.S. Naval Test Pilot School at NAS Patuxent River, Maryland. Following graduation from USNTPS in June 1961, as part of Class 28, he was test pilot for three years in the Carrier Suitability Branch of the Flight Test Division at NAS Patuxent River. His work there included both land-based and shipboard tests of the F-8E, TF-8A, F-8E (attack), and A-4E aircraft and the automatic carrier landing system. In 1962, as project officer on the F-8 Crusader new jet trainer, Williams, then a Captain, became the first pilot to land a two-seat jet on the aircraft carrier from the rear cockpit.