Theodor Arps (* 2 February, 1884 in Garmisch-Partenkirchen † 28 April 1947) was a German naval officer, most recently Deputy Admiral in World War II, from 1940 to 1945 Judge at the Reichskriegsgericht. Theodor Arps was most known for managing the German Naval Intelligence Service (German:Marinenachrichtendienst), the German naval intelligence organization from 1st October 1934 to 31st December 1939. Arps time at the Marinenachrichtendienst was known for increased rearmament at the agency, a modernizing period, preparing and undertaking assurance testing on the Naval Enigma for secure message use cases (which was insecure), training and mobilization planning and an increasingly efficient and modern signal intelligence architecture that was the culmination of two decades of work during the interwar period.
Theodor Arps entered the Imperial Navy on 1st April 1902 as a sea cadet, completed his basic and then ship training on the cruise ship SMS Stein and then came from the 1st April 1903 to the 30th September 1904 to the German Imperial Naval Academy. After successful training, his transfer took place on board the scheduled ship SMS Wettin, where he was promoted to Lieutenant on 29nd September 1905. As a company officer, he changed to the 2nd Torpedo Division on October 1, 1906, and was there as a guardian on various torpedo boats. On 1st May 1909, the transfer of the Lieutenant to the Sea (since 30th March, 1908) took place for a year as the first officer on the station ship SMS Loreley. Then he was used until 30 September 1911, again as a security officer, on the battleships SMS Posen. Subsequently, there were commandments for training purposes in the ship artillery with subsequent transfer to the ship artillery school in Kiel-Wik as an instructor. On January 18, 1913, Arps was sent as a security officer to the Light cruiser SMS Stuttgart, where he was promoted to Kapitänleutnant on July 15, 1913.