Description of a German U-Boat

Answer 1

From the Russo-Japanese War in 1904 (the first German U-boats were from the batch purchased by Russia in 1904) thru WWII; they all had the same general silhouette; a narrow body with tapered ends (fore & aft) and a conning tower.

Like tanks, planes, and surface warships, it usually takes a trained eye (from the men that man those machines) to identify the particulars...e.g. (for example) telling the difference between an M48A2C Patton tank from a M48A3 Patton tank...no one would know the difference except a tanker (tank crewman).

For your information, the A3 Patton tanks were diesel engined; the A2C model had a gasoline engine, plus some other interior changes. But from the outside, only an armor crewman would know the difference between the two. Same for submarines.