Basically the German navy was split into two geographical commands, Nordsee and Ostsee (Baltic). The Schiffsstammdivisionen were for basic training (as opposed to specific advanced trade or specialist training) that sailors were allocated to before joining their ship or shore unit. Initially there were two Detachments for each of the Nordsee and Ostsee Divisions (1A and 2A) but due to the massive expansion in the Navy the Divisions were later broken down into three Regiments for each of the Nordsee and Ostsee commands and ultimately further into numerous Abteilungen. The suffix is actually a Frakturschrift "A" (for Abteilung), not a "U".
So the ribbon is a pre-war example for the 1st Abteilung of the Baltic training Division (being an early band it can also be found in block script for the Reichsmarine )
Wow! Thank you Redcap I couldn't have asked for a better reply