What were the features and the purpose of submarines in WW1?

In the First Word War military submarines made a significant impact for the first time. The German U-Boats enjoyed a great deal of success and were responsible for destroying around half of all the food and supplies transported by the British Merchant Navy. During WW1 Germany built 360 U-Boat submarines, 178 of which were lost. In total they were responsible for the loss of more than 11 million tons of allied shipping.