What were U-boats in World War I?

U-boats were an advanced type of submarine used by Germany during World War I and II. They were responsible for sinking several civilian ships during the beginning of World War I and served as dangerous and stealthy weapons in military conflicts in both wars.

U-boats relied on torpedoes as weaponry and were typically capable of traveling fully submerged for two hours. The Treaty of Versailles, which marked the end of World War I, prohibited Germany's possession of U-boats but did not prevent the country from researching U-boat technology, resulting in the more advanced U-boats that were used by Germany in World War II.