Hitler did everything during the war to achieve his goals of war. So, and when it comes to the sea lines between America and Europe, he tried everything to cut them off. In order to achieve this, he used U-Boats, known for its use in the First and Second World War. These boats are effective in combating the enemy navy, but they are also very effective in the naval blockade of enemy shipping. That's exactly what Hitler did, these ships blocked shipping channels.
