Actually, SS, after I wrote that I saw IABL's great suggestion (
here, with my subsequent comment) which effectively made my above post redundant!
I'm with you - give the Kaleun a Lloyd's Register and Weyers Taschenbuch der Kriegsflotten and let him record what he sees, with subsequent confirmation (or not) from BdU.
Maybe not something for the more casual players though, so maybe an option...