The Answer:

The following refers to the German Imperial Navy's conversion of Germany's first commercial submarine, the Deutschland, to submarine cruiser (U-155). Various reports with further details were cited here last Friday.

Mystery question:
There were a total of eight boats of Deutschland's merchant class subs built, plus Bremen. Because of their original, merchant design, there were only two 20-inch torpedo tubes both in the bow. How heavy was their surface gun battery?

The Answer:

Deutschland's high freeboard and wide beam permitted a relatively heavy deck gun battery of two 5.9-inch (150mm) and two 3.4-inch (88mm) guns. source: The U-151 Class, U-Kreuzer - SteelNavy.com. '...Intended for serious boat-studiers. - Wall Street Journal, April 27, 2004

Submarine history buffs will enjoy the fascinating details and photos of the Kaiser's U-Boats found in the preceeding link.