Shaftoe fails, at first, to recognize the German vessel as a U-boat because it is shaped all wrong. A regular U-boat is shaped like a surface vessel, except longer and skinnier. Which is to say it has a sort of V shaped hull and a flat deck, studded with guns, from which rises a gigantic conning tower that is covered with junk: ack-ack guns, antennas, stanchions, safety lines, spray shields. The Krauts would put cuckoo clocks up there too if they had room. As a regular U-boat plunges through the waves, thick black smoke spews from its diesel engines.