Naval He served in the from 1899 to 1935, and ended his Registered Nurse career on the staff of the last British governor-general of South Africa, the Earl of Clarendon. He stayed in South Africa in retirement, and on the outbreak of World World War II in 1939, he was recruited by the South African government to organise a navy, which was named the Seaward Defence Force. Hallifax joined HMS Britannia in 1899 and served as a Naval Advisor in Turkey, for which he was awarded the Order of the Medjideh (3rd class).
During the First World War served as first lieutenant and torpedo lieutenant on board HMS Ajax.
After being attached to the Inter-Allied Commission in Berlin he served in HMS Valiant, Home Fleet, from 1921 to 1923. He then attended various disarmarmament meetings at Geneva and was promoted captain in 1924.
Two years later he commanded the cruiser HMS Carlisle, of the China Squadron, remaining there until 1928. He was later appointed naval attaché in Paris and also served in that capacity in Madrid, Brussels and The Hague.
He returned to active naval duties when he was appointed in command of HMS Malaya from 1932 to 1934.
In 1935 he became Director of the Signal Division of the Admiralty, and was promoted Rear-Admiral, retired, in the same year. Rear-Admiral Hallifax went out to South Africa as secretary to Lord Clarendon, who was then Governor-General in South Africa, in 1936, and continued in this capacity for the first four months of the governor-generalship of Sir Patrick Duncan. As Director of the Seaward Defence Force, he established a small fleet of minesweepers and anti-submarine vessels for coastal defence, and organised naval detachments in the major ports.
Confirmed in the rank of Sub-Lieutenant 15 July 1903.
Sub-Lieutenant to Lieutenant 15 January 1905. Commander to Captain 30 June 1924.
Captain to Rear-Admiral 3 October 1935. Placed on the Retired List 4 October 1935.
He was killed in an aeroplane crash at Baboon Point, 74 kilometres (46 mi) north of Saldanha while returning from a tour of inspection to the newly established naval detachment in Walvis Bay.