The First World War brought radical changes to the Submarine with Diesel and Electric systems being developed At the start of the war the Germans followed the rule of "Prize Rules" which allows the crew of the captured vessel to leave the sink before sinking the ship but after a period of time the Germans adapted to unrestricted warfare tactics.

At he very start of the First World War Germany had 48 submarines built and had 29 that were functional. In the first 10 weeks of the First World War Great Britain lost five cruiser ships to German U-Boats Great Britain had 77 submarines at the start of the First World War operating in the Baltic and Atlantic Sea as well as the North Sea,Mediterranean and the Black Sea.