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Battle of Atlantic Sections
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  The Climax, 1943 <<<
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Books by John Barratt

Armada 1588

The Battle of Marston Moor

The Civil War in South-West England 1642-1646

The First Battle of Newbury: 1643

Cavalier Generals

The Great Siege of Chester

The Battle for York: Marston Moor 1644

Cavalier Generals

The U-boat War, The Climax, July 1942-May 1943
The U-boat War, The Climax, July 1942-May 1943
by John Barratt

By July 1942 the days of easy pickings for the U-boats along the Eastern Seaboard of the USA were over. It was time for Donitz to switch his efforts back to his old hunting grounds in the mid-Atlantic. He had seemingly ample grounds for optimism. In May 1942 German experts had produced a study which concluded that if the U-boats were able to sink a monthly average of 700,000 tons of Allied merchant ships for the rest of the year, Britain, despite all the efforts of shipbuilding yards on both sides of the Atlantic, would be doomed.

Though this was more than twice the average monthly sinkings for 1941, Donitz felt confident of success. At the end of 1941, his U-boat fleet had totalled 236 vessels, which had been sinking 13 Allied merchant ships for every one of their own number lost. They had reduced the total available British merchant fleet by 3 million tons compared with the start of the war. And now Donitz was returning to the Atlantic convoy routes in a stronger position. He had a total U-boat strength of 331, of which 141 were operational and an average of 50 constantly on patrol. U-boat HQ at Chateau Kernival in Brittany had become expert in the close orchestration of the increasingly effective "wolf-pack" tactics. 

Even more significantly, and often overlooked in favour of the better-known Allied successes in breaking the Enigma codes, the German cryptologists at "B-Dienst" had pierced the Royal Navy codes giving details of the assembly points and sailing times of convoys, often giving U-boat HQ between 10 and 20 hours advance warning of enemy intentions. Just as valuable was German success which between February 1942 and June 1943 frequently enabled them to read the daily British Admiralty estimate of U-boat dispositions, though like the Allies, the Germans had to forgo using much information to avoid the enemy suspecting their success. 

Despite the steadily increasing numbers of escort vessels becoming available for the convoys, increased air support, and technological advances in anti-submarine warfare, the results of the U-boat war in the second half of 1942 seemed to justify Donitz's hopes. During the last few months of the year, aided by the diversion of many Allied escorts to support the "Torch" landings in North Africa, the U-boats were sinking a monthly average of 650,000 tons. If the vessels sunk by aircraft, mines and such few surface raiders as were still at large were added to this total, Germany seemed on the verge of achieving the sinking rate demanded by her experts.

Unfortunately for Donitz's hopes, his planners had seriously underestimated Allied , particularly American, construction capacity. During 1943 US shipyards would produce 20 million tons of merchant shipping, ample to replace a total Allied loss during the previous year of about 7 ½ million tons, overestimated by the Germans as twice as much. Though there had been many apparently striking U-boat successes, such as the attack in August on convoy SC94, which had lost 26 ships, and the November assault on SC107, which sank 15 ships, these were deceptive. In fact, therefore, though not fully appreciated by either side, or indeed by many modern historians, at the end of the year the U-boats were no closer to decisive victory. Furthermore, the steadily increasing effectiveness of Allied anti-submarine measures was hinted at by the less favourable , for the Germans, sinking ratio, now running at 10 merchant ships for every U-boat lost.

The Decisive Months

It was apparent to both sides that the first half of 1943 would be decisive. Donitz began the year believing that the rate of sinkings being achieved by his crews was slightly outpacing the rate of Allied shipbuilding. His U-boat fleet had now increased to 400 vessels, of which 200 were operational, and an average of 100 at sea -10 more than the total which, at the start of the war, Donitz had argued would have been sufficient to bring decisive victory, although his estimates then had not allowed for US involvement.

Yet Allied effectiveness was also increasing. There were now over 500 escort vessels available, sufficient not only to provide stronger close protection for convoys, but also to allow the formation of "support" or hunter-killer groups, to reinforce convoys under attack. Equally significant were the on-going advances in anti-submarine warfare being made by the Allies. During the autumn of 1942 the increasingly effective air operations against U-boats crossing the Bay of Biscay in transit to and from their French bases received the welcome assistance of airborne radar. For a time in the autumn of 1942 the U-boats were given some protection against this threat by a radar detection device, but in February 1943 the Allies introduced a new short-wave radar which proved undetectable until the closing stages of the war.

Although it is unclear whether Donitz had fully grasped the fact, by the beginning of 1943 there were unmistakable signs that, if it had ever really existed, the window of opportunity for a decisive German victory in the Battle of the Atlantic was closing rapidly. The first four months of the year saw the rapid introduction by the Allies of a whole range of improved anti-submarine equipment and techniques. As well as improved aircraft-mounted radar, escort carriers were beginning to prove their worth and surface escorts were being equipped with radar, high frequency direction finders and improved anti-submarine weapons such as the "hedgehog" depth charge thrower.

Not only were escorts and aircraft proving more effective, there were also more of them. Between February and May the number of long-range "Liberator" anti-submarine aircraft available rose from ten to over sixty. Although the vast majority of US Navy escort vessels had been diverted by the needs of the Pacific War, leaving the RN and RCN to perform about 96% of escort duties in the North Atlantic, increasing the size of convoys had made it possible to raise the average number of escorts from six to nine, without increasing the vulnerability of the convoy. Sufficient escorts had also been released to allow the formation of five British convoy-support groups, the best known being that operating out of Liverpool under Captain J. F. "Johnny" Walker. They were later reinforced by a US group. Each group consisted of between five and seven destroyers and frigates, and three also had an escort carrier. Their role was to accompany convoys through the mid-Atlantic air gap., where they were most vulnerable to attack, whilst the presence of an escort carrier helped provide air support for the entire crossing.

Of equal, though again often underrated significance, was the success by now consistently being achieved by the Allied radio direction finders. Between July 1942 and May 1943 they managed to divert 105 out of a total of 174 North Atlantic convoys away from wolf-pack ambushes, and enabled another 23 partially to avoid such traps. Only 16 ran into large U-boat concentrations, and it was these which suffered the bulk of losses.

Despite all these favourable portents for the Allies, the first three months of 1943 saw continued notable U-boat successes. They were aided in part by wintry conditions in the North Atlantic, which made Allied detection less effective, and also by the introduction of the new U-boat Enigma cypher known to Bletchley Park as "Shark", which remained unbroken until the end of March.

In February convoy ON 16 lost 14 ships, with the overall merchant ship/U-boat kill ratio for the month standing at 7:1, a decline from the German high point of the previous year, but still offering U-boat Command grounds for hope.

The particularly foul weather of March, with convoys and their escorts straggling through gales, blizzards and hail, saw some of the fiercest battles of the war. The beginning of the month saw roughly 50 U-boats at sea. Between 7-10 March, convoy SC 121 lost six ships, with 199 men of their crews, experienced seamen who could be less easily spared than their ships. The next two convoys, SC 122 and HX 229, were even more savagely mauled by 44 U-boats from wolf packs Sturmer, Dranger and Raubgraf - the greatest U-boat concentration achieved in the entire war. A total of 22 ships of 146,000 tons were lost between March 8-18. But tragic though the loss of merchant ships and their crewmen was, of ultimately greater significance was that throughout the entire battle, the U-boats had failed to sink or damage a single escort vessel, whilst seven of their own number had been damaged, with two U-boats being sunk later by Allied aircraft on their way back to base.

By April the tide had begun to turn. Though battles were once more fiercely contested, the Allies lost only half as many merchant ships as in March, whilst 14 U-boats were accounted for.

Feeling the battle slipping away from him, Donitz ordered a supreme effort for May. The decisive action came in the first week of the month with a concerted attack on convoy ON 55. After initial German successes, the balance tilted with the arrival of a Royal Navy support group, assisted by fog which hindered U-boat operations. On 5/6th May a total of 7 U-boats were sunk compared with 12 merchant ships. It was the beginning of a disastrous trend for Donitz. By the end of May he had lost from all causes 41 U-boats , more than a quarter of his operational strength, for barely the same number of Allied merchant vessels. The losses, as Donitz, admitted, were "intolerable". On May 24th he ordered all but a token number of U-boats away from the North Atlantic in what was termed "a temporary shift to areas less endangered". Though no one would be sure of it for a long time to come, Germany had lost the Battle of the Atlantic.
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Copyright © 2002 John Barratt.

Written by John Barratt. If you have questions or comments on this article, please contact John Barratt at:

About the author:
John Barratt has authored many books to include: Armada 1588,  The Battle of Marston Moor, The Civil War in South-West England 1642-1646, and Cavalier Generals.

Published online: 12/15/2002.
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