For anyone that sees this but does not know...
The U-Boat is the same thing as a Submarine!
1: Wilhelm Bauer - Made the first submarine
-He was German, so he likely made these for the military.
2: World War 1: The first ships to fall victim to the u-boats were in ww1 including the HMS Pathfinder
3: Battle of Bell Island: The whole cause of the conflict was because a small group of german u-boats attacked some ore-carriers.
Hope this helps!!