Cecil was intelligent, good looking, popular and good at all sports. 
After the Philberds School, Maidenhead, Berks, he entered Britannia (training ship) as a naval cadet in 1894.  On promotion to Lieutenant in 1900 he gained five "firsts", the Beaufort Testimonial, the Goodenough medal and the Ryder memorial prize.  
He qualified as a French interpreter.
In 1902 he was appointed to specialise in gunnery. He invented a quick firing pom-pom gun and a "fall of shot indicator" patented in 1912. This was first used at the Battle of Jutland. It registered the actual fall of each shot and enabled the necessary correction of each gun to be made with precision. 332 were supplied to the British navy. The Paravane was another of his inventions which was used in both world wars. This helped the safe navigation of a ship through a minefield. In 1920 he was awarded £6,000 by the Royal Commission on Awards to Inventors.
He became Deputy Director National Ordnance, Head of the Gunnery Division of the Naval staff, vice-president of Chemical warfare Committee and Director of the Senior Officer Tactical school.
In 1914 he was Commander on the Battleship Colossus in the Grand Fleet. In June 1916 he took part in the Battle of Jutland. The Colossus was hit twice with five casualties.  Later he commanded the mine-layer Latonia in the eastern Mediterranean. He was senior naval officer in Salonica and Corfu in 1917/18. He commanded the Cruiser Dragon, and battleships Malaya and Resolution.
He was a trustee, chief organiser and vice-president of the 6 nation "Indian Defence League of America", set up around 1920 to promote the interests of American Indians.
He was appointed Rear Admiral in 1928 and became Head of Naval intelligence (1930-1931).  
He retired from the Navy before world war 2 and in 1934 was an under- writing member of Lloyds.
At the beginning of world War 2 he became Director General of the Press & Censorship bureau under the Home Office. He resigned to become joint managing director (with Noel Macklin?) of a ship construction firm building Fairmile motor launches.  In 1941 he was  recalled to Admiralty for "special services" until 1945.
Pam Usborne writes: "Henry, while an MP in the late 1940's, had a pied-a-terre in the admiral's house in Gordon square, London. He was frightfully good looking, with an eye for the ladies. Carryll would compete with her daughter over boyfriends. In spite of this Vivian always adored her mother." 
Carryl took the view that his career might have advanced even further had he spent as much time being nice to men as he devoted to women.