Clarence Howard-Johnston was born on 13 October 1903; he was educated at the Royal Naval Colleges, Osborne [Isle of Wight] and Dartmouth [Devon]. In 1955 he married Paulette, daughter of Paul Helleu.

Howard-Johnston's naval service included: Midshipman (1921); Commander (1937); Director of Studies, Greek Naval War College, Athens (1938-40); Naval staff, anti-submarine Warfare Division, Admiralty (1940); detached to set up anti-submarine training, Quiberon [France] (1940), and commanded operations for destruction of port facilities at St Malo, and the evacuation of British troops from St Malo and Jersey (for which he was mentioned in despatches); anti-submarine operations in the Norwegian fjords, and the evacuation of troops and wounded from the Norway Campaign at Molde and Andalsnes (for which he was awarded the DSC); in command of an anti-submarine escort group in the North Atlantic (1941-42), escorting 1,229 ships (and being awarded the DSO for sinking the submarine U651); serving on the staff for the Battle of Atlantic Command, Liverpool, (1942-43); Captain (1943); Director of the Anti-U-boat Division, Admiralty (1943-45), during which time Howard-Johnston was anti-submarine specialist at the Prime Minister's Cabinet U-boat meetings; in command of HMS Bermuda, British Pacific Fleet and occupation of Japan forces (1946-47); Naval Attaché, Paris (1947-50); Naval aide to the Queen (1952); Rear-Admiral (1953); Chief of Staff to Flag Officer, Central Europe (1953-55); retired, 1955 (being awarded the CB).

Howard-Johnston was also an inventor of simple hydraulic mechanisms, and was commended by the Admiralty for the invention and development of anti-submarine training devices including the Johnston Mobile A/S target, in 1937. He died on 26 January 1996.