Until 30 September 1925, he underwent a number of military and naval training courses. It began with basic military training (1 April – 30 September 1921) in Stralsund at the Baltic Sea and weapons courses at the Naval Academy at Mürwik. Hartmann was then transferred to the (1 October 1921 – April 1922) for onboard training and then to the training ship "Niobe" (April – 30 June 1922). During this timeframe, he advanced in rank to "Fähnrich zur See" (officer cadet) on 1 April 1923 and to "Oberfähnrich zur See" (Senior Ensign) on 4 April 1925.