It sounds more like what you're doing here is writing a paper on the cultural history of u-boats rather than a social history of them. The former would be much easier to accomplish as a social history would be far more difficult as the u-boat and its men composed only a fraction of Germans in uniform in both world wars, so their "footprint" on German society would be harder to trace and probably necessitate field work within Germany among various veteran organizations. But a cultural history of the u-boats would be easier and there is a fine book on this subject, Count Not the Dead: The Popular Image of the German Submarine which should give you a nudge in this direction.