The Battle of the Atlantic was one of the most important fronts in World War II. In September 1939, Germany immediately sought to capitalize on Britain's dependence on imports of food and raw materials. After the Wehrmacht attacked it in June 1941, the U.S.S.R repeatedly asserted its dire need for imported equipment and supplies. Meanwhile, the Allies had to wrestle control of the seas to support several second fronts, first in North Africa, then Italy, and finally western Europe. The United States, British, and Canadian navies worked together to overcome losses inflicted by German U-boats and Luftwaffe bombers, but the issue remained in doubt until 1943.
From the U.S. perspective, the struggle moved through three phases. When the war began in Europe, the U.S. maintained neutrality while also increasing the readiness of its fleet. After signing the "Two-Ocean Navy" legislation in the summer of 1940, President Franklin Roosevelt next pushed to assist Britain. In August 1940, he arranged a loan of older destroyers in exchange for the use of British bases in the Western Hemisphere. The following March, he secured passage of the Lend-Lease Act to enable a cash-starved Britain to receive equipment and supplies and then pay for them later. In May and July 1941, U.S. forces occupied bases in Greenland and then Iceland.
During this early period, Germany had aimed to avoid directly engaging American naval forces, but the two countries drifted closer to war in the months preceding Pearl Harbor. On September 4, 1941, a German submarine, after being attacked by a British plane, fired torpedoes at Greer (DD 145) in waters south of Iceland. Greer responded with 19 depth charges. Neither opponent scored a hit, but the incident freed President Roosevelt to authorize Navy crews to fire at German U-boats upon sighting. On October 31, 1941, U-552 torpedoed and sank Reuben James (DD 245), the first U.S. Navy ship lost to enemy action in WWII.
Although its readiness improved before formally being at war, the Navy was inadequately prepared for the ferocity of the German assault it faced in the second phase of the Battle of the Atlantic. U-boats announced their presence off the eastern coast of the U.S. by sinking the steamer Cyclops on January 12, 1942. The enemy's Operation Drumbeat continued for months as German submarines hunted tankers and merchantmen. The Navy had too few destroyers and subchasers to screen the coast while also escorting merchantmen or troop ships in the Atlantic. Inadequate numbers of aircraft, whether from the Navy or the Army Air Corps, also limited patrolling. From January through April, German submarines sank over 80 merchantmen off the East Coast and 55 north of Bermuda. By May, merchantmen began sailing in convoys as the Navy increased the number of ships and aircraft and improved their crews, training, which prompted U-boats to shift to easier targets moving through the Gulf of Mexico and the Caribbean.
This striking series of photos from July 1943 shows attacks on German U-boat bys aircraft from a U.S. Navy escort carrier. (NH-111313, NH-111308, NH-111284, and NH-111311)
American escort forces delivered 100,000 troops and their equipment for Operation Torch in North Africa in the fall of 1942, but Germany continued to reposition its boats and hunt effectively in more weakly protected areas until the third phase began in May 1943. By then, British and Canadian forces had begun to provide effective defenses for the North Atlantic convoys and Admiral Ernest J. King established himself as commander of Tenth Fleet. Charged with directing the Americans' antisubmarine efforts in the Atlantic, the organization had no assigned ships but employed innovative scientific efforts to maximize the effectiveness of offensive and defensive techniques. Very long-range scout and bomber aircraft using new radar helped close gaps where submarines had enjoyed freer rein. Accompanying the convoys, increasing numbers of escort carriers and destroyers now directed a deadly combination of air and sea-delivered munitions at the submarines. Meanwhile, British interception of German message traffic provided valuable intelligence about U-boat locations. U.S. industrial production of naval vessels and merchantmen also began to make its weight felt.
After much had sunk in frigid waters since the war's beginning, the tide had turned by the middle of 1943. German U-boat crews bravely fought on, but at a distinct disadvantage that meant Allied planners could more confidently plan and execute their land campaigns in Europe. The Allies had prevailed and showed innovation and tenacity in the process. But success came after relearning old lessons.
As in World War I, some naval leaders were slow to react to the threat posed by German submarines. Sending merchantmen in escorted convoys had proved to be vitally important in 1917-18, but in early 1942 officials waited months before insisting on this tactic. Conflicts arose over whether to prioritize the defensive effort of protecting the commercial vessels or the offensive option of attacking submarines. The Battle of the Atlantic also demonstrated a key relationship between technology and training. Advances such as sonar and radar could provide the Navy's escorts an advantage over the submarines, but they did so only after crews received adequate training. Finally, the beginning of WWII also revealed that such early periods in conflict often display a level of unpreparedness that becomes palpable only after the fact.