After his degree, national military service awaited him. He spent it as an officer in the Army Physiological Unit and Deputy Director for Scientific Research. He subsequently returned to the United States, to a fellowship at the
Medical College of Virginia at Richmond. Over the years he was appointed to many commissions in the United Kingdom and elsewhere. Among his professional research interests was
diabetes mellitus. His appointments included one as Professor of Experimental Medicine at
Guy's Hospital. In 1970 he was invited to accept the position of
Vice-Chancellor of the
University of Nottingham. In 1976 he was appointed
Regius Professor of Physic at the
University of Cambridge where he led the re-establishment of the
School of Clinical Medicine, University of Cambridge. In 1978 on the death of Sir
Morien Morgan he was elected Master of
Downing College, Cambridge, where he was a popular figure. Even after retirement from the post, his links with his adopted College persisted and he did what he could to further its interests. The College bar at Downing is named after him. The Mastership of Downing led to a term also as
Vice-Chancellor of the University of Cambridge. ==Honours==