Are you sure that the paint and material are safe for the fish? Usually, I think fish tank ornaments are made of such materials (usually resin, but I'm not an expert in the area
). Still, looks cool though.
BTW - you can get actual U-Boat models for fish tanks - I see them on eBay all the time. I think the model was of a VIIC, but I'm not sure now. I've also seen a Bismarck wreck for fish tanks, although it was in a lot better condition than the actual Bismarck wreck.