Army Air Forces in World War II

The Battle of the Atlantic: July 1942-May 1943

During the AAF's antisubmarine reorganization, the most important battle of the antisubmarine war in the EAME theater raged in the North Atlantic. Following the policy of seeking the most lucrative targets, Adm. Dönitz redeployed most of his U-boats to the North Atlantic in July 1942. The Allies responded by providing aerial coverage for escorted convoys crossing via the great circle route between ports on the east coast of the United States and Great Britain--except for a five-hundred -mile gap between 25º W and 45º W longitude. Dönitz deployed his wolf packs in screens at both ends to intercept convoys sailing into the gap. The eastern screen fell entirely in the EAME theater.

Dönitz soon had the advantage of superior tactical intelligence while British intelligence faltered. At the onset of the war, Britain had successfully deciphered enemy military codes encrypted by a German code machine called Enigma. This intelligence, known as Ultra, was one of the most important secrets of World War II. In February 1942, the German navy replaced the Enigma machine from the Atlantic U-boat network with a more complex version that created codes the British could not decipher for the rest of the year. Redirecting the convoys on a short notice to avoid wolf packs was hopeless. The Germans also began reading the Allied convoy code in February and used the information to intercept the convoys.

Free from aerial attack and supplied with exceptional intelligence, the U-boats could take advantage of other Allied difficulties in the North Atlantic. Between September 1942 and March 1943, fuel shortages forced shipping convoys to take the shortest track, the great circles routes across the North Atlantic. Meanwhile, the winter weather created rough seas and limited visibility, which frequently allowed the submarines to approach convoys undetected.

By August 1942, eighty-six German submarines were hunting in the North Atlantic; this number remained virtually constant until June 1943, except for a brief period in November and December 1942. Exploiting Allied handicaps, the Germans successfully located and intercepted convoys during this time more frequently than at any other time in the war: from August to November, they sank seventy ships in the North Atlantic. Over those four months, Germany lost thirty-three submarines to Allied attacks, one in a collision, and another to a mine. Seventeen of the losses occurred in the North Atlantic. The Allies damaged only seven U-boats during convoy attacks.

Following the Allied assault landings in North Africa on November 8, 1942, the Germans redeployed most of their submarines from the North Atlantic to the mid-Atlantic, off the northwest African coast, and in the approaches to the Straits of Gibraltar. A relatively small force--twenty to thirty submarines compared with the normal force of eighty to ninety--continued to harass North Atlantic convoys in November and December. The Germans sank twenty-one ships, but lost only one U-boat.

In December, the scales began to tip in favor of the British. Cryptologists began again to decipher the German U-boat code. By March 1943, the Allies confirmed what the British had suspected the previous December: the Germans were reading the Allied convoy code. The Allies finally instituted a new code in June 1943 to confound enemy intelligence operators. By August, the British were reading German messages almost as soon as they were intercepted. The Allies had regained the advantage in the intelligence battle.

Early in 1943, the Germans retained the strategic initiative in the Battle of the Atlantic. The submarine offensive severely threatened the Allies' ability to transport cargo. In the last quarter of 1942, the United States began to build merchant ships rapidly enough to offset losses inflicted by the U-boats. For their part, the Germans were building enough submarines to replace their losses and increase the number of operational U-boats at sea.

At an Allied conference in Casablanca, Morocco, in January 1943, the Allies adopted a renewed resolve. Great Britain and the United States agreed to give the war against the German submarines first priority. Modified B-24 aircraft would be used to patrol the North Atlantic aerial gap because escort carriers were not yet available. After the conference, the British immediately began operating antisubmarine B-24s from bases in Ireland and Iceland to cover the eastern part of the gap.

In the meantime, Dönitz positioned most of his operational U-boats against the North Atlantic convoys. The submarines sank 31,700 tons of Allied shipping for every U-boat lost from January to March 1943. Eighty-five ships succumbed to the German submarines, at a cost of only eight U-boats. In April, the AAF Antisubmarine Command moved three B-24 squadrons to Newfoundland to cover the western half of the gap. Two AAF units, the 1st and 2d Provisional Bombardment Flights, began flying a few B-25D Mitchell bombers on convoy coverage from Blue West One, an airfield on Greenland.

Meanwhile, the U.S. Navy deployed its first escort carrier to close the North Atlantic gap in aerial coverage. The combination of the new carriers and the use of Ultra information to direct convoys around the U-boat screens effectively neutralized the

German submarine offensive. In April and May 1943, the Allies lost thirty-eight ships totaling 218,000 tons in the North Atlantic convoy battles, but between April 25 and May 20, they destroyed sixteen U-boats engaged in attacks on convoys. In these two months, the Germans sank 13,625 tons of Allied shipping for every submarine lost, about half the ration for March. So, on May 25, Dönitz withdrew virtually all German submarines from the North Atlantic, essentially conceding victory to the Allies in the Battle of the Atlantic. Almost 1,700 Allied ships crossed the ocean in June and July 1943 without any losses.

Following the defeat in the North Atlantic, Dönitz changed U-boat strategies. Rather than trying to disrupt transatlantic supply lines, he switched to a more defensive strategy of tying down large Allied antisubmarine forces in widely scattered areas. Small groups of submarines deployed to the east coast of the United States, the Caribbean Sea, the coast of Brazil, the Atlantic coast of North Africa, and the Indian Ocean. In the long run, those U-boats had minimal effect on the war, and German submarines could not retard the buildup of Allied forces in Great Britain preparing for the invasion of occupied Europe.