I have written about submarines several times (here and here). It doesn’t take much imagination to feel how terrifying, dangerous and challenging it was to serve on a submarine. The crew was certainly made up of adventurous young men like the sailor in this photo.
The Kappenabzeichen attached to the post shows the activities of the dive boats. This was primarily a disruption of commercial traffic (cargo ships) during the Great War. Warships were more likely to be encountered by chance. I think it’s also because submarines were ordered to the busy shipping routes, they moved rather random and not according to a precise plan of action. “Free hunting” may have been their motto. Of course, they were hunted by the surface vessels and also from the air.