Atlantic, battle of the

Atlantic, battle of the, popular name for the six-year struggle from 1939 to 1945 to secure the Atlantic routes vital to Allied victory. It was not, therefore, a battle in the traditional sense like Trafalgar, Jutland, or Midway, but rather a long fight to organize, protect, and manage the movement of war materials and shipping efficiently in response to the conflicting pressures of global war. To win in the Atlantic the Allies had to overcome more than the Germans. The Germans, in turn, never possessed the forces to achieve victory.

The shooting war in the Atlantic was actually a series of campaigns, in which the immediate and long-term objectives of German strategy varied while those of the Allies remained essentially constant. For the Allies the Atlantic war had three objectives: blockade of Axis Europe, security of Allied sea movements, and the freedom to project military power overseas as required. The preponderance of Allied naval power meant that the blockade was never seriously challenged (but see blockade runners). Allied amphibious warfare potential took time to develop, but that was due to the limits of air and land forces and depended on the availability of suitable landing craft. Security of trade movements at sea posed the greatest problem for Allied navies due to the small, but powerful and modern, German surface fleet and more importantly the Germans' innovative use of submarines.

The battle of the Atlantic was therefore a response to German initiatives, since most objectives of Allied strategy could be met without direct attack on Germany's maritime interests. The initiative in the Atlantic fell on the Kriegsmarine (German Navy), a service woefully unprepared for a major naval war. The massive expansion of Raeder's ‘Z’ Plan of 1939 would have provided the required forces, but not before 1944 (see Germany, Table 11). When the Kriegsmarine found itself at war with the UK in September 1939 naval planners were left to wonder ‘What now?’

German naval strategy during the phoney war was thus an adjunct to the main thrust in the west by the army and air forces. The Kriegsmarine harassed and contained Allied naval forces through a war on shipping conducted largely by surface ships. These included the heavy units of the main fleet (see German surface raiders), as well as auxiliary cruisers, but although dramatic, these operations were never more than a qualified success. The fleet made a major contribution to the invasion of Norway in April 1940, but suffered crippling losses. The importance of U-boats remained to be demonstrated during the phoney war, and torpedo failures marred their contribution to the Norwegian campaign.

The battle began in earnest after the fall of France in June 1940. That collapse gave impetus to the naval war in two ways. First, French and Norwegian bases partially allowed the Germans to overcome the Allied blockade, permitting breakout through the Greenland–UK gap and giving them advanced bases on the Atlantic. Second, the collapse of western Europe provided the Kriegsmarine with a clear and simple strategic objective with potential war-winning results: defeat of the UK by severing her maritime communications. It was this battle, begun in earnest in the late summer of 1940, that Churchill dubbed the battle of the Atlantic. It was, in fact, the only time in the war when the Germans were within a measurable distance of victory at sea (see Graph for comparison of losses, September 1939– May 1945).

Unfortunately the Germans had no way to measure the distance accurately and lacked the means to execute the strategy. Karl Dönitz, commander of the U-boat fleet, estimated that if Germany destroyed 600,000 to 750,000 tons of British shipping per month for a year the UK would sue for peace. German ‘certainty’ of the scale of the task contrasts sharply with British knowledge about their shipping and import situation. Attempts in 1938 by the British to estimate their requirements and shipping resources failed to produce uniformly agreed results. It seemed that the UK needed 47 million tons of imports per year, and that British shipping alone could handle the requirement. The availability of neutral shipping for some carriage would easily fill the gap to achieve the UK's estimated peacetime import total of 50–60 million tons.

To attack this amorphous target the Kriegsmarine applied all its resources over the winter of 1940–1, but they were unequal to the task. Large raiders ended up either blockaded in French ports or destroyed, and the loss of the Bismarck in May 1941 effectively ended attempts to use heavy ships in the Atlantic. German surface raiders caused the Allies anxiety, but their destruction of Allied shipping was negligible: only 6.1% of shipping destroyed by Germany during the war. By comparison, 6.5% was accounted for by mines, 13.4% by aircraft, 4.8% by unknown causes, and some 70% by U-boats. As the last figure indicates, Germany came to rely on its U-boat fleet. Dönitz had long argued that only a submarine campaign would defeat the UK and that this required 300 ocean-going U-boats. In August 1940 he had only 27 for operations and over the winter of 1940–1 the number available declined, to a low of 21 in February. Moreover, only about a third were on station at a time: 13 in August 1940 and only 8 in January 1941. The number of U-boats increased dramatically in the spring of 1941, but by then Dönitz's chance had passed.

German U-boat operations in the second winter of the war were none the less highly successful; their innovative tactics caught the RN by surprise and produced the first ‘Happy Time’ for German submariners. Through the first year of the war the Allies defended shipping by routeing it away from danger, sweeping inshore waters with aircraft to keep U-boats down and immobilized, aggressive patrolling, and escorting ocean convoys with a mixture of forces appropriate to the threat. Since it was believed that air power and convoys forced submarines to operate inshore and submerged, anti-submarine (A/S) escort extended initially only to 12° West. Beyond that convoys were protected by cruisers, battleships, and even Allied submarines. Submariners could move further seaward in search of easy targets, but once away from the channelling effect of coasts, where shipping routes converged, targets and good firing positions were difficult for individual submariners to obtain.

Dönitz developed a system to solve both the search and the attack problems on the high seas. The search problem was resolved by establishing patrol lines of U-boats perpendicular to the convoy route, controlled by a shore-based plot through high-frequency radio communications. Acting like a huge drift net and manoeuvred on the basis of intelligence, these ‘wolf-packs’ covered a wide area of open ocean. Once in contact with a convoy, shadowers from the pack transmitted position reports to the shore staff, who then directed the pack on to the target, and sent a medium-frequency homing signal to draw in the pack. Attack on the convoy followed once a number of U-boats were assembled, and it was left to the individual submariners to conduct it. Typically attacking at night, the U-boats slipped inside the escort screen and often inside the convoy itself on highspeed surface runs. Initially defence against such attacks was so feeble that U-boat captains could pick the biggest targets and fire all their loaded torpedo tubes before retiring. Escape was simply a fast run astern of the convoy or, if pressed by an escort, a quick dive.

The RN was unprepared for this type of warfare and losses to some convoys were alarming. At the end of October 1940 SC7, a slow east-bound convoy of 30 ships, lost 21 of its number and HX79, a fast convoy following close behind, lost 12 of its 49 ships. The British responded in several ways, but the main thrust was the progressive denial of both tactical and strategic surface manoeuvrability to the U-boats. Over the winter of 1940–1 steps were taken to extend the range of naval and air anti-submarine escort, culminating in the establishment of bases in Iceland in April 1941. In the same month a distinct Western Approaches Command was established in Liverpool to co-ordinate and oversee defence of trade convoys from submarine attack.

Icelandic bases permitted defence of convoys by small ships to about 35° West, but a gap remained in A/S escort between Iceland-based forces and those from the convoy terminals in Canada. In May 1941 the Royal Canadian Navy (RCN) moved to Newfoundland to fill that gap and in June began escorting convoys between the Grand Banks and Iceland (see Newfoundland Escort Force). The air gap between the limits of Iceland and Newfoundland-based aircraft remained for another two years and profoundly affected the development of the battle (see Map 1).

Providing ocean A/S escort for convoys did not defeat the German attack: Dönitz's tactics were designed to cope with escorted convoys. Although some notable U-boat ‘aces’ were killed or captured early in the year, the Germans had little trouble from escorts during 1941. The Allies lacked an effective, modern radar to detect U-boats on the surface at night, tactical responses to successful penetrations of the escort screen were still primitive, and the teamwork required for escort group cohesion was still developing. What ‘saved’ the UK in the spring of 1941 was a generally improving situation. Imports had declined sharply over the winter of 1940–1 as the UK adjusted to closed east coast ports, as weather-damaged shipping lay idle, and as demoralized European merchant seamen obstructed sailings. These problems eased as winter gave way to spring, the UK adjusted to new shipping patterns, requirements were sweated down to essentials, the USA moved alongside, and war with the USSR drew German attention. Moreover, German success in the war against tonnage fell far short of expectations—and of the typically inflated claims by U-boat captains. Merchant shipping losses over 1941 amounted to 3.6 million tons—an average of above 250,000 tons per month—of which 2.1 million fell to U-boats. The savings in British tonnage from rationalizing imports and reducing port congestion during 1941 amounted to about 3 million tons, while some 1.2 million tons of new merchant shipping were launched. The UK actually ended 1941 with a surplus in tonnage. Over the same year it imported only about half of its estimated pre-war rate and much less than the amount thought necessary for waging war. In 1942 the UK would manage to live and fight—just—on approximately 23 million tons of imports. Moreover, in 1941 the prospect in the short term looked good as over 7 million tons of new shipping was on order in US yards. Only for brief periods in 1942 and 1944 did the UK draw on its reserves of key commodities; in all other years imports outpaced consumption.

The U-boat war in 1941 was therefore dramatic but not decisive. Despite some dips and alarms the tonnage available to carry the UK's imports remained remarkably constant (see table, UK, 9). The official British history of wartime shipping concludes that there was little wastage in the management of British shipping during the war, although port delays reduced efficiency and diversion to other tasks, such as the build-up of forces for the Normandy landing in June 1944 (see OVERLORD), cut sharply into import programmes. In contrast, it is estimated that American wastage of carrying capacity was prodigious, reaching perhaps 9 million tons a year by 1945—three times the total American tonnage lost to enemy action in the war.

The winter of 1940–1 was the only time the Germans could have achieved a decisive victory in the Atlantic, and they failed. From the summer of 1941 until the spring of 1943, then, German strategy aimed to embarrass Allied plans and forestall the development of the Second Front. In this they enjoyed a modicum of success. But several new elements weighed heavily against Germany in the Atlantic by mid-1941. The invasion of the USSR in June 1941 (see BARBAROSSA) drew German air strength east, and drew U-boats into a defensive posture off Norway by November in response to Hitler's fears for his northern flank. British persistence in the battle for the Mediterranean also drew U-boats there by the autumn. By the early summer of 1941 the British had achieved a major breakthrough in the German U-boat cipher system (see ULTRA, 1), and by August they were reading Atlantic U-boat signal traffic with some regularity and rapidity. This, along with the general intelligence picture derived from conventional means, allowed convoys to be routed well clear of danger for much of the period. It was not a perfect system, and some rather dramatic battles around slow convoys developed in September and October. One historian has argued that ULTRA saved 300 ships for the Allies in the last half of 1941, a figure that is impossible to refute—or to verify conclusively.

The other major change in the Atlantic war during 1941 was the increasingly active involvement of the USA. The US Navy's participation in defence of shipping followed Roosevelt's and Churchill's historic meeting in August at Placentia Bay, when they divided the world into spheres of strategic control. The USA took control of the western Atlantic, including Iceland and in mid-September the USN began to escort fast convoys between the Grand Banks and Iceland, working alongside the Royal Canadian Navy (RCN) which took responsibility for slow con voys. The USN was therefore involved in the battles around Canadian-escorted slow convoys in September and October 1941. The Canadians performed so poorly and slow convoys were so vulnerable that one was sent back to Canada when confronted by a U-boat concentration. German withdrawals to the Mediterranean and Norway eased the crisis around the slow convoys by November, while moves were afoot to reinforce the beleaguered Canadians.

The Atlantic war entered a new phase after the Japanese attack on Pearl Harbor in December 1941. American industry and manpower gave the Allies promise of victory, but in the meantime vast new theatres for Axis attack were opened up. For the Germans the most important of these was the eastern seaboard of the USA, where a rich harvest of Allied shipping sailed virtually un protected. The first victim fell on 12 January 1942 and by the spring individual U-boats were enjoying their second ‘Happy Time’. In May and June alone U-boats sank over a million tons in US waters—half their total score for 1941 in two months. Allied merchant shipping losses peaked in 1942: according to the USN's official history, some 8.3 million tons were lost to enemy action. By British estimates, 6.1 million tons of this fell to U-boats, which averaged over half a million tons per month. It was the closest Dönitz got to his earlier objective, but it could not be sustained. The curve of new shipping construction surged past losses in the autumn of 1942, as American industry gained momentum. Moreover, the U-boats' success in the western Atlantic was the result of a monumental American strategic blunder.

Like the British in 1939–40, the Americans in 1942 trusted in offensive patrols by surface and air forces, protected lanes, and independently routed coastal shipping to defeat the U-boat menace. The result was one of the real disasters of the war. U-boats enjoyed freedom of movement inshore as patrols and merchant ships proceeded independent of one another along predictable routes. Routine patrols made operating areas more secure for U-boats, while individual ships made easy victims. Only the progressive extension of a convoy system within a wide and effectively patrolled air corridor reduced the threat from lone submariners. The quality of the naval escort, the basis for much American concern since they preferred destroyers and there were too few of these, was less important than the system. Air patrols made wolf-pack operations impossible, while convoys eliminated easy victims and threatened U-boats with counter-attack. Even if a lone U-boat could find a convoy it could anticipate only one good shot before the escort reacted and the convoy evaded the attacker. As this system was extended, the ratio of Dönitz's basic formula for success—the amount of tonnage sunk per U-boat day at sea—was reduced, and forced U-boats to move on. Much of 1942, then, saw the progressive denial of operating areas for U-boats dependent upon surface manoeuvrability for both tactical and strategic success.

American failure to institute a coastal convoy system immediately has mystified historians, but recent Canadian scholarship sheds light on this issue in two ways. First, the infrastructure needed to establish a convoy system was in place by the end of 1941. The Canadians ran, on behalf of the British, a naval network which controlled shipping in major American ports, and in early 1941 the USN was brought into it. Ottawa was privy to intelligence as it affected merchant shipping, and controlled shipping movements in the western Atlantic until the Americans took over in July 1942. The Anglo-Canadian system, with local help, could have organized a convoy system from American ports at the end of 1941. Secondly, American delay in establishing convoys probably owed more to doctrinal issues, and was no doubt the result of experience alongside the struggling Canadians in late 1941. The USN's predilection for offensive measures and belief that poorly escorted slow convoys were dangerous, as was demonstrated in September and October 1941, clearly carried more weight than advice from the British.

By September 1942, New York had become the western terminus for transatlantic convoys, and a complete interlocking convoy system extended into the southern hemisphere. In the process the Allies abandoned Iceland as a relay point for transatlantic escorts, and convoys sailed between the Grand Banks and Ireland with a single Mid-Ocean Escort Force group, which could make the passage provided the convoy stayed close to the great circle route. With the Germans busy elsewhere restricted routeing was not a problem, but it made the main routes more vulnerable when wolf-packs returned to the air gap in the autumn. By September 1942 the soft theatres were gone, and the Atlantic war reached its moment of decision.

The winter of 1942–3 is the most complex period of the Atlantic war. Allied fortunes changed dramatically, with victories at Stalingrad, Guadalcanal, and in the North African campaign. Offensives put more demands on shipping, while North African operations drew more heavily on British war reserves than planners had anticipated. The situation was further complicated by drawing the escorts needed for the North African landings from the direct UK–West Africa convoy route. Thereafter all south Atlantic shipping was routed through the western Atlantic convoy system and to the UK along the main routes. This ex tended sailing times and reduced carrying capacity. The UK therefore became utterly dependent on the main convoy routes just as the Germans were driven to attack them in force. As a final point, the situation was further aggravated by the fact that the bulk of new merchant shipping was American (see USA, 7) while the vast majority of losses were British. These broad strategic developments therefore pushed the UK into its gravest import crisis of the war just as the battle in mid-ocean built to a climax. The Germans returned to the air gap in increasing numbers in August 1942, with enough U-boats to operate two large packs. Over the next eight months the number of packs and their size increased dramatically.

The naval and air tactics, doctrine, and equipment necessary to deal with wolf-packs had improved markedly by 1942. Air patrols previously hovered directly over convoys, or patrolled over vast areas in support of several convoys. By 1942 air patrols were synchronizing their efforts more effectively with convoy movements by flying slightly ahead and on either side of a convoy's line of advance to forestall the assembling of a pack: these tactics also produced more sightings. The introduction of white paint schemes, which made aircraft harder to spot, higher patrol altitudes, and more effective fuzes for depth charges (see anti-submarine weapons) contributed to more and more successful air support. In August a few specially equipped very long range (VLR) Liberator aircraft penetrated to the depths of the air-gap, a development noted with concern by the Germans. Naval escorts now enjoyed the benefits of 18 months of steady operational and tactical leadership, the development of sound and workable tactics and doctrine, and new equipment. The latter included 10 cm. radar with an automated 360° sweep, which made it possible to establish an effective barrier around the convoy at night in good weather. The assembly of the pack around the convoy could now be forestalled by ship-borne High Frequency Direction Finding sets (see huff-duff), which revealed the position of U-boats sending contact and shadowing reports. Destroyers of the escort screen raced out and drove the U-boats off. Shipborne HF/DF was not completely successful (destroyers had to conserve fuel), but it usually reduced the number of attackers that the radar barrier had to handle. The only element missing from the naval escort in 1942 were small escort carriers which, like so many other resources, had been drawn off for the North African landings and the Arctic convoys.

These developments affected the dynamic of convoy battles. Good leadership, group familiarity, and the tactical intelligence provided by modern sensors allowed the six RN mid-ocean groups to win their battles in late 1942. It helped that the RN escorted the bulk of the fast convoys. The other five groups, four of them Canadian and one nominally American, lacked modern equipment and enough destroyers, and their convoys—the bulk of them slow—were easy marks for German submariners. The results were hardly surprising: Canadian escorted convoys accounted for 80% of mid-Atlantic losses from July to December. It was, in fact a repeat of autumn 1941. The British were so alarmed that they removed Canadian groups from the mid-ocean for several months in early 1943.

The only bright spot for the mid-Atlantic at the very end of the year was the re-penetration of the Atlantic U-boat cipher. The gap in this part of the ULTRA picture had endured since February, but with individual U-boats roving inshore enough intelligence was available from conventional sources and other decrypts to keep track of them. However, as the mid-ocean filled with U-boats precise intelligence became increasingly crucial. Through the winter of 1943 the number of operational U-boats ranged from 403 to 435, with an average of more than 100 at sea each month, most in the Atlantic. Dönitz, who became head of the Kriegsmarine in January 1943, had his magic number and a free hand.

The battle of the Atlantic reached a climax in early 1943, building to a crisis for the Allies very quickly, spurred by bad winter weather, the rising numbers of U-boats, and another gap in ULTRA intelligence in the first three weeks of March. The situation was so bad in early March that all North Atlantic convoys were located by the Germans, half were attacked, and some 22% of shipping in those convoys sunk. The grim news brought alarm to the Allied camp, but the seeds of the German defeat were already sown. In January 1943 Churchill, Roosevelt, and their senior advisers met in Casablanca (see SYMBOL) to plot Allied strategy. Pressured by the need to get on with the build-up for the Normandy landings and the mounting UK import crisis, the Allies finally gave the Atlantic first priority. With that decision the longstanding pleas by naval authorities for more VLR aircraft, more destroyers, and escort carriers to eliminate the air gap found fertile ground. By late March support groups, one of them with a carrier, were established to reinforce convoy escorts during their transit of the air gap. In March, as well, the allocation of VLR Liberator aircraft was finally agreed at the Washington Convoy conference and by May they were making their presence felt in the mid-Atlantic. The Allied offensive in the air gap was aided immeasurably by moderating weather in April, which gave freer rein to the escorts' radars and ‘Huff-Duff’ directed destroyer sweeps.

ULTRA's re-penetration of the main U-boat cipher in the third week of March allowed these resources to be applied with devastating results. Since not all convoys could now be routed clear of U-boats, routeing and reinforcement were used to draw U-boats into a battle of attrition they could not win. The RN was prepared to trade the loss of two merchant ships for the certain destruction of a U-boat in the spring of 1943, as confrontations were sought and U-boats punished heavily. VLR Liberators closed the air gap in May, and more escort carriers arrived to join the battle. Nearly 100 U-boats were sunk in the Atlantic during the first five months of 1943: 47 in May alone (see Map 6). At the end of May, Dönitz withdrew his battered packs: as far as the course of the war was concerned, the battle of the Atlantic was decided by the spring of 1943.

Historians point to the decisive role of ULTRA in the Atlantic war, particularly in early 1943 when the German defeat followed quickly after the breakthrough in late March. However, the elimination of the air gap would have defeated the wolf-packs without ULTRA, although special intelligence allowed it to happen faster and with more telling effect. It was air power that forced submarines to operate fully submerged as a normal mode. Maritime air power, directed by ULTRA, also devastated the U-boat fleet when it attempted to renew the offensive with acoustic homing torpedoes in late summer. Air power held the U-boat in check for the balance of the war.

The decisiveness of the Allied victory over Germany's submariners in 1943 was a highlight in the naval war, and most histories of the Atlantic end there. As far as the war itself is concerned, the scale and drama of the victory over the U-boats were of less importance than the check in shipping losses it represented. These were already a localized and declining proportion of Allied tonnage by late 1942. Allied shipping losses from January to May 1943 averaged 450,000 tons per month, most of this to U-boats. In the last seven months losses averaged approximately 200,000 with only about 40–60,000 tons accounted for by submarines. To the victory of 1943 can be added the opening of the Mediterranean in the summer and the enormous volume of new construction from American yards over the year. An open Mediterranean improved the usefulness of available shipping, while Allied shipyards launched 14 million tons of new shipping in 1943, outstripping losses by about 11.5 million tons. Unfortunately for the UK, the new shipping was almost entirely American and only Roosevelt's intervention gave the British access to it. Shortages of shipping and strict regulation by the UK's ministry of war transport plagued British action for the balance of the war, while the percentage of British controlled shipping under bareboat charter (that is, without crews) increased substantially. These factors contributed to the UK's post-war economic crisis. It remains to be demonstrated, however, whether war losses of shipping materially affected the course of the war.

Marc Milner

Bibliography

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Milner, M. , North Atlantic Run: The Royal Canadian Navy and the Battle for the Convoys (Toronto, 1985).
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