A new topic for Kriegsmarine pictures. I'm starting with these hard to find pictures from S.D.O. rookies. The Stammabteilung der Ostsee was a navy school for young recruits who were taught how to sail in the Baltic. I suppose they were bases in the Kiel area , but I haven"t found too much about these guys yet. The cap tallies clearly show the name of this unit and all 4 pics belong to the same guy.
For several reasons the instruction was on small sail ships. Firstly this was a cheap way to learn how to sail and secondly this respected the Versailles Treaty as the sloops were way under the maximum size and went unnoticed. These men are most probably recruits from the mid-1930s and one can easily imagine they late rmade perfect sailors for the wartime. Maybe some of these became famous soldiers.
According to this source, the SDO Abteilung was founded in 1930/31 and was incorpoorated in the KM in 1933 under the name of Marinestation der Ostsee. The pictures with SDO names on the tallies must be from 1930-1932, Reichwehr period, which would suit my previous analysis regarding the Versailles Treaty preconisations . https://de.wikipedia.org/wiki/Gliederung_der_Kriegsmarine