In 1922, aged 14, he joined the Royal Navy as an officer cadet, and in 1926 was appointed to the cruiser HMS Frobisher, with the rank of midshipman.
During this time Gwinner and Lulworth were assigned to the West Africa convoy route, escorting ships to and from Freetown, Sierra Leone.
in April 1943 after a short spell back with Duncan Gwinner was given command of the sloop Woodcock, and assigned to FJ Walker's 2nd Support Group.
[6] In December Affleck was torpedoed and declared a constructive total loss;[7] Gwinner transferred his pennant to Balfour, and continued operations, but had no more successes.
At the end of the war Gwinner left the Royal Navy and moved to the US where he became director to an American container company, retiring in 1971.