[1] Willis completed his officer training in 1940 and was posted to the heavy cruiser HMAS Canberra, joining the ship on Boxing Day.
He remained with Canberra until December 1941 when he joined the British destroyer HMS Kingston which was engaged in escorting convoys traveling from Egypt to Malta.
He was removed from this position and transferred to navigation duties, however, following an incident in which a large number of practice rounds were fired without being aimed.
At the start of 1945 he was posted to the British Pacific Fleet as executive officer of HMAS Barcoo and saw action with this ship in the Dutch East Indies until the end of the war.
At the end of this course he was promoted to lieutenant commander and was a senior instructor with the Royal Navy's navigation training school HMS Dryad for two years.
He commanded the naval contingent which lined the streets of Melbourne during the 1956 Summer Olympics before moving to a shore posting in December that year.
He attended the Imperial Defence College in London in 1967 and served as director-general of operations and plans in the Navy Office for three years when he returned to Australia.
On 13 June 1981, he was appointed a Knight Commander of the Order of the British Empire for his service to the RAN, becoming the last CNS to receive this honour.