Passage: The first practical submarines were developed in the late 19th century, but it was only after the development of the torpedo that submarines became truly dangerous (and hence useful). By the end of the First World War submarines had proved their potential. During the Second World War Nazi Germany's submarine fleet of U-boats almost starved Britain into submission and inflicted huge losses on US coastal shipping. The success of submarines led to the development of new anti-submarine convoy escorts during the First and Second World Wars, such as the destroyer escort. Confusingly, many of these new types adopted the names of the smaller warships from the age of sail, such as corvette, sloop and frigate.

Question: When did submarines finally prove their potential?
the end of the First World War