Lieutenant Colonel John Halliday Croom was educated at Glenalmond and Gonville and Caius College, Cambridge. He graduated in medicine in Edinburgh in 1933. Before the Second World War he was an undergraduate clinical tutor at the Edinburgh Royal Infirmary. where his duties included teaching medical students the elements of clinical examination.
He served throughout the war in the Royal Army Medical Corps in France, the Middle East, Malta and Italy, being mentioned in despatches and reaching the rank of lieutenant colonel. He returned to the Royal Infirmary of Edinburgh in 1946 as a consultant physician, holding this appointment until he retired in 1974.1