U-boat is a short word the German word Unterseeboot meaning submarine
https://www.youtube.com/watch?v=dzaMP5ZXryU
Germany reacted by using its submarines to destroy ships that were supplying other countries The U-boats (unterseeboots) controlled the Atlantic armed with torpedoes. they had a double hull, engine, and a single torpedo tube. the ww2 had two torpedo tubes. The u-boat had the first diesel engine installed in a German navy boat.
the schooner is a boat with lots of sails it is used for carrying passengers fishing cargo and also used as racing boat. the boat looks like a pirate ship and is all run by the wind. if you were on a schooner you would feel the wind on your face and see the ocean washing the side of the boat.
pontoon bridge is a floating bridge supported by hollow boats. the bridge is used for vehicle use and some pedestrians. the bridge weight limit was 60 tons exceeding the weight limit could have been fatal and ended in death or loss of military equipment.
a cleat is a knot that is wrapped around a T shaped piece of metal this is probably the strongest knot that keeps the boat in place.