The term U-Boat comes from the German wordUnterseeboot A U-Boat is basically what its literal term means: an undersea boat The only difference between a U-Boat and a Submarine is the usage of it in the English Language. Germans use the term U-Boat to describe ALL undersea vessels, while Americans differentiate a submarine and a U- Boat.
The main purpose of a U-Boat is to attack merchant ships carrying supplies. This was so the other countries were unable to successfully fight back in the war (no supplies= no competition= victory for the opposite side). A U-Boat was able to attack these ships unnoticed… it could see the vessels from under the water, which allowed them to sink them and remain undetected.
The U-Boat modernized naval warfare in World War I. They set standards for naval forces and required opposing forces to come up with better techniques and tactics to conquer the undersea vessels. The initial German strategy of World War I was to destroy all Allied merchant shipping. This eventually failed because escorted convoys were introduced. 360 U-Boats were built by Germany for the War. After the War, 178 were lost, but Germany was able to sink 11 million tons of shipping.