Vice Admiral John Knowles Im Thurn, CB, CMG, CBE (7 March 1881 – 5 July 1956) was a British Royal Navy officer who was Assistant Chief of the Naval Staff from 1931 to 1933.

[1] In August that year he was posted to the torpedo boat depot ship HMS Vulcan, serving with the Mediterranean Fleet.

[2] He served in the First World War, mainly with wireless telegraph and signalling duties, and was promoted to the rank of captain on 30 June 1918.

He was captain of HMS Hood from 1923 to 1925, during which time the ship participated in a promotional tour of various ports around the world, the World Cruise of the Special Service Squadron.

He served in this position until 1933, when he was appointed commanding officer of the 1st Cruiser Squadron in the Mediterranean Fleet.