A gunnery expert, he developed a fire control system for British warships, and served as flag captain to Admiral Sir John Jellicoe at the Battle of Jutland.

Dreyer was reappointed to the Hawke on 13 January 1903[4] for another trooping voyage to Malta, and when she was paid off in March, he was appointed to the staff of HMS Excellent, then under the command of Captain Percy M. Scott.

[1] In 1904 Exmouth became the flagship of the British Home Fleet whereupon he became gunnery advisor to the Commander-in-Chief, Admiral Sir Arthur Wilson.

[1] On his return, and upon the recommendation of Admiral Wilson, Dreyer was promoted commander and appointed an Assistant to the Director of Naval Ordnance (DNO), John Jellicoe.

[1] At the end of 1907 he assisted in the trials of Arthur Hungerford Pollen's Argo rangefinder mounting and plotter on the cruiser HMS Ariadne.

He returned to the Admiralty, under the new DNO Captain Reginald Bacon and remained there until 1909, when he was appointed commander (executive officer) in the new dreadnought HMS Vanguard, then completing in Barrow-in-Furness.

[1] At the behest of Jellicoe, now Commander-in-Chief of the Grand Fleet, Dreyer was made flag captain of HMS Iron Duke, serving at the Battle of Jutland in 1916.

[1] Following the Armistice he was appointed commodore, 2nd class and served as Chief of Staff to Admiral Jellicoe on his Naval Mission to India and the Dominions on HMS New Zealand, between 1919 and 1920.

However, the tainting by association of the Board of which he was part by the Invergordon Mutiny in 1931, with the consequent effect on that fleet, meant that Dreyer was destined never to command it.

[1] He was on the staff of the General Officer Commanding-in-Chief, Home Forces in 1940 as an advisor on anti-invasion measure, before becoming Inspector of Merchant Navy Gunnery (1941–1942).

His second son was the late Vice Admiral Sir Desmond Dreyer, who also became a gunnery officer, won the Distinguished Service Cross at the Battle of the River Plate, and went on to become Second Sea Lord.

Both camps aimed to produce a combined mechanical computer and automatic plot of ranges and rates for use in centralised fire control.

The Dreyer Table had some mechanical flaws, particularly when additional loads were introduced in the form of unauthorised accoutrements concocted by individual gunnery personnel, but on the whole performed in a satisfactory manner.

At the same time Dreyer applied for a similar grant but due to the fact that in 1915 he had been awarded £5,000 for his services to fire control his request was denied.