The Battle of the Atlantic was the longest campaign of World War II. From 1939 to 1945, German U-boats sought to sever the lifeline of supplies crossing the ocean to Great Britain. At first, Allied losses were staggering. Merchant ships were sunk faster than they could be built. But the Allies adapted. Convoys protected by naval escorts, new technologies, and growing air power slowly turned the tide. By 1943, the balance had shifted. Though the Atlantic remained a battleground, millions of Ameri