I have many of David Doyle’s (et al) Squadron Signal and Legends of Warfare books. They are all terrific references. My go-to for photo documentation (and not so much technical) of the Kriegsmarine is Breyer and Skwiot’s hefty “German Capital Ships of WWII.” Covers DKM Deutschland/Lutzow, Admiral Scheer, Admiral Graf Spee, Scharnhorst, Gneisenau, Bismarck, and Tirpitz in detail. Also the Classic Waships paperbacks by Steve Wiper.