The German U-Boat, or submarine, took a large toll on American shipping in the early stages of World War II. It could have been even more devastating, but the Germans made some mistakes. However, the Allies made plenty of mistakes too, and that helped the Germans have success at times.
The Germans hoped to disrupt supply lines from the Americas to Europe during the war. Even before the war started, there were some philosophical errors that led to the how the battle for supremacy in the Atlantic Ocean shaped up. The military wisdom of the day focused on having big surface warships. Neither side really understood the impact submarines could have.
Germany had restrictions on its surface ships, that had been put in place after World War I. Submarines were not given much attention. This opened the door for Germany to develop under water technology. It did to some degree, but the chief of the German Navy was still committed to surface ships. The Luftwaffe was also competing for dollars. As the war heated up in 1939, the Germans had some Uboats, but if they had more, they could have been untouchable on the ocean.
According to an article by the New England Historical Society, the U.S. government hid the reality of Uboat attacks along the east coast. In the first six months of 1942 the Germns destroyed 20 percent of the American tanker fleet, singing 233 ships and damagine many more.
Finally, U.S. officials took the advice of the British, who had already tangled with the Uboats. They advised the use of convoys, which surrounded cargo ships with fighting ships to ward off attacks by Uboats. This was an effective strategy.
The British also created hunter groups to go after the Uboats, but this had little success. Radar was not good enough to detect them far below the surface, and often the submarines went by undetected.
Germany captured Norway and France, which gave them much better access to the Atlantic, and that helped their cause greatly. The Germans made a huge mistake however, by having a strong central control over the subs. Before the convoys were very organized, central control allowed them to more effectively attack unprotected ships. However, as the Allies began breaking German code, it became harder for them to do.
The Allies eventually created a tracking system, and after they broke German codes, they could tell where the Uboats were and where they were going.
The U.S. eventually started avoiding the Uboats instead of engaging them, and that was effective.
A mistake the British air force made was to bomb industry. Bombers were not used to combat Uboats at all, but many think they could have been effective.
The battle for the Atlantic lasted for the duration of the war, but after about 1943, United States ships were able to get supplies to Europe without losing very many to Uboats. The Allies won the battle of the Atlantic eventually, and the wear, but made mistakes as well.