||Entering the service in 1893, Dewar specialised in gunnery. He was a lieutenant in 1900 and became a commander in 1911. In 1912 he won the Royal United Service Institution Gold Medal for his essay on the influence of overseas commerce on the operations of war and its past and present effects. He was Assistant Director of the Plans Division of the Admiralty in 1917, was promoted to captain in 1918 and commanded cruisers on the North America and West Indies Station, 1922 to 1924. Between 1925 and 1927 he was Deputy Director, Naval Intelligence Division. His command of the ROYAL OAK in the Mediterranean in 1928 ended in the notorious 'incident'. In 1929 he became a rear-admiral, was retired the following day and advanced to vice-admiral in 1934. During the Second World War, however, he served again at the Admiralty. He stood as Labour candidate for Portsmouth in 1931. Dewar was one of the founder members of The Naval Review and a strong advocate of naval reform and of improved staff training.He wrote an autobiography, 'The Navy from within' (London, 1939).
||The papers were presented in 1966 by Dewar's widow, Mrs Gertrude Dewar. They consist mainly of letters received, including some from Admiral Sir Herbert Richmond (q.v.) and drafts and memoranda relating to Dewar's Admiralty service, there being little official or other correspondence relating to his career afloat. Private and family letters, and papers concerning the court-martial arising out of the ROYAL OAK affair, were presented subject to certain conditions and access to them was restricted. These restrictions expired in 2003. There are also diaries kept for both the First and Second World Wars official service documents.