The attack on Pearl Harbor and the subsequent German declaration of war on the United States had an immediate effect on the campaign. Dönitz promptly planned to attack shipping off the American East Coast.
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The U.S., having no direct experience of modern naval war on its own shores, did not employ shore-side black-outs. The U-boats simply stood off the shore of the eastern sea-board and picked off ships as they were silhouetted against the lights of the cities.
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The first boats started shooting on January 13, 1942, and by the time they left for France on February 6 they had sunk 156,939 tonnes of shipping without loss.

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