[3] Kennedy-Purvis became one of the Navy's early wireless telegraphy specialists, and after promotion to commander in June 1915 was appointed an instructor at the newly formed RN Signal School.

He served as the executive officer of the cruiser Southampton in 1918–1919, and of the battleship Ajax in 1919–1920, then returned to the Signal School as its commander, having been promoted to captain in December 1921.

[5] In June 1935 he was appointed to the Board of Admiralty[6] as an Assistant Chief of the Naval Staff with special responsibility for Fleet Air Arm affairs.

In the West Indies, Kennedy-Purvis successfully surmounted any difficulties and within a very short time was working in closest co-operation with his American counterpart.

[1] On 5 November, 1941, in front of a Guard of Honour provided by the Royal Marines detachment of Despatch, Kennedy-Purvis unveiled a monument to the crew of HMS Jervis Bay at Albouy's Point, in Hamilton, Bermuda, from where Jervis Bay had departed on her final mission (Bermuda was a formation point for trans-Atlantic convoys in both World Wars.

[12] In late 1942 he was recalled to England to become the Deputy First Sea Lord,[13] an appointment created to relieve the First Sea Lord Admiral of the Fleet Sir Dudley Pound of the burden of his administrative duties, allowing him to concentrate on his role as Chief of the Naval Staff and a member of the Chiefs of Staff Committee.