Submarine Typ 212 at HDW in Kiel, Schleswig-Holstein, Northern Germany

The German Type 212 class, aka Italian Todaro class, is a highly advanced design of non-nuclear submarine developed by Howaldtswerke-Deutsche Werft for the German and Italian Navies. It features diesel propulsion and an additional air-independent propulsion system using Siemens proton exchange membrane compressed hydrogen fuel cells. It can operate at high speed on diesel power or switch to the AIP system for silent slow cruising, staying submerged for up to 3 weeks without surfacing and with no exhaust heat. The system is vibration-free, extremely quiet, and virtually undetectable. Type 212 is the first fuel cell propulsion system equipped submarine series. Read more. 

Historically, it was the Germans who invented the U-Boot. It was first designed in 1850 by the inventor and engineer Wilhelm Bauer and built by Schweffel & Howaldt in Kiel for the Imperial German Navy. “U-boat” is the anglicized version of the German word U-Boot (short for Unterseeboot = undersea boat).