Ellis first distinguished himself as a naval aviator during World War II, during which time he earned commendations for service in the North African Campaign and, later, valor awards for his leadership as Commander Air Group 18 aboard USS Intrepid.

[1] William plead with his family to consent to his enlistment in the Navy, which was agreed to on the condition that he earn appointment to the United States Naval Academy.

After attending nearby Werntz Preparatory School in Annapolis and receiving the backing of his district's congressional representative Charles Manly Stedman, he entered the academy in 1926 and graduated in 1930.

During Operation Torch Ellis primarily remained on the carrier as fighter director officer, though he did lead one flight over Moroccan territory.

Ellis was awarded the Air Medal for "skillfully directing his group in its first combat operation" for the month of September 1944, comprising strikes against the Palau's and the Philippines.

He flew three consecutive ten-hour days throughout the engagement, confronting two geographically distinct enemy formations both containing capital ships.

[10] Ellis served as air officer up until April 1945, when Intrepid suffered its fifth kamikaze crash and had to return to port for extensive repairs.

[11] After the war, Ellis served as CO of the Fleet All Weather Training Unit Atlantic, at Naval Air Station Key West, Florida.

Specifically recognized in his full citation are Ellis's adroit management of an Atlantic command at a time when the Vietnam War pulled increasing Navy resource to the Pacific; and the swiftness with which he assisted in the recovery of a hydrogen bomb lost off the coast of Spain.

[8] Ellis's final position within the Navy was as chief of staff to the Supreme Allied Commander Atlantic, a post he served in during his last year of service, 1968.