Peril on the sea

In March 1941, Churchill christened Nazi Germany’s assault on Britain’s imports and maritime communications “The Battle of the Atlantic.” Historians continue to employ this term as a convenient shorthand, though Churchill’s label is misleading in some respects. The deadly contest between German U-boats and Allied convoys was not actually an Atlantic battle but a single, protracted campaign. It was, in fact, the longest campaign of the Second World War, from September 1939 until Germany’s collapse in 1945. The fighting also spread far beyond the confines of the Atlantic Ocean: this was a global war on shipping.

Gradual strengthening of British defenses along the North Atlantic sea lanes caused the Germans to seek easier targets. Whether in the Indian Ocean, the Arctic or Pacific, their goal was simply to sink enough merchant ships to cripple the Allied war effort. It did not much matter where those ships were destroyed. Nor did they rely entirely on submarines to get the job done. U-boats were undoubtedly Germany’s most effective commerce raiders, accounting for over two thirds of Allied and neutral merchant ship losses. But many vessels were also lost to German aircraft, mines, and surface raiders.

Churchill and the Atlantic

No one knew better than Winston Churchill the high stakes in this contest. The British war effort would rapidly break down if deprived of imported raw materials, munitions, oil, and food. The Atlantic battle was “the dominating factor all through the war,” Churchill recorded in his memoirs. “Never for one moment could we forget that everything happening elsewhere, on land, at sea, or in the air, depended ultimately on its outcome, and amid all other cares we viewed its changing fortunes day by day with hope or apprehension.”¹

Elsewhere in his memoirs, Churchill claimed that “The only thing that ever really frightened me during the war was the U-boat peril.”² These are frequently quoted words from his memoirs of the Second World War. Still, the image of the Prime Minister watching anxiously as shipping losses rose and imports fell tells only part of the story. Churchill took considerably less interest in the day-to-day management of the anti-U-boat war than his memoirs suggest. When he did become directly involved, it was because shipping losses were beginning to approach crisis levels. And even then, Churchill was always reluctant to give the war against U-boats first claim on British resources.

The First Phase (June 1940-December 1941)

As Churchill became Prime Minister in May 1940, the war on shipping was entering a new and more dangerous phase. Germany’s conquest of Norway and France provided Hitler with a network of new bases. From these, his navy and air force could intensify their assault on Britain’s maritime communications. Yet their long-term threat was overshadowed in the summer of 1940 by the prospect of a full-scale German invasion.

Churchill naturally focused on meeting the more immediate threat to Britain’s survival. To bolster Britain’s defenses, he supported the Admiralty’s decision to strip the Atlantic convoy routes of destroyers, corvettes, and other light craft so that the Royal Navy could maintain the strongest possible anti-invasion patrols along the south-east coast of England.

The depletion of convoy escorts led to a sharp increase in losses to U-boats during the second half of 1940. Churchill was not initially alarmed by this development. In the short term, Britain was in a good position to absorb these losses. Its merchant fleet was still the largest in the world, and its strength had been augmented by nearly two million tons of shipping acquired from Continental states overrun by the Germans.

The anti-invasion patrols offered an additional benefit that Churchill was eager to exploit. If the Navy could keep the German army away from Britain’s shores, resources could be diverted to the Middle East. There Britain could come to grips with Hitler’s Italian ally. From Churchill’s perspective, this was too good an opportunity to pass up. Even as Britain’s fortunes reached their lowest point in the summer of 1940, he was determined not to let British strategy become completely defensive.

Sustaining imports

Churchill assumed a more active role in the war at sea in early 1941, after months of heavy shipping losses threatened to reduce import levels to a point that would endanger Britain’s military operations in the Middle East. He was unwilling, however, to endorse the Admiralty’s remedy of more aircraft to protect merchant shipping. Import levels had not yet become critical, Churchill insisted. Britain’s long-range aircraft should be concentrated on offensive action—the bombing of Germany, rather than trade protection.

Churchill’s efforts to bolster imports were focused, therefore, on making optimal use of existing shipping resources. To this end, he created a new War Cabinet sub-committee in March 1941, the Battle of the Atlantic Committee, with himself as chair, to bring together the departments and individuals most concerned with the shipping and supply situation. Over the next few months, the Committee achieved some notable successes. By July, the amount of shipping requiring repair had been decreased by nearly a million tons, The turnaround time of merchant ships in port was significantly reduced; and congestion in British ports was brought under control. At the same time, Churchill successfully lobbied the United States for assistance. In April he persuaded President Roosevelt to increase the presence of American warships and aircraft in the North Atlantic.

Turning one corner

These developments enabled Churchill to report encouragingly to a secret session of the House of Commons in June 1941. Despite heavy losses in recent months, he noted, Britain was on track to meet import targets for the coming year. This was always Churchill’s bottom line. His optimism was encouraged by the massive expansion getting under way in the American shipbuilding industry, which might soon be able to replace all the British vessels being sunk by the Germans.

The shipping situation improved considerably during the second half of 1941. Between February and June, an average of 125 merchant ships had been lost each month. From July to November, the figure dropped to 50. Numerous factors contributed to the sudden improvement: increases in the number of escort vessels, improved equipment and training, the growing effectiveness of RAF Coastal Command aircraft, a decrease in the number of ships sailing independently, and intelligence breakthroughs that temporarily allowed the decryption of U-boat signals.

The drop in shipping losses was especially encouraging, given the large expansion of the German U-boat fleet during 1941. Taken together, these developments persuaded Churchill that the U-boat threat had been reduced to manageable proportions. In August 1941 he told General Hastings Ismay that “he was inclined to think that the corner had been turned in the Battle of the Atlantic and that the drop in the rate of sinkings might be maintained.”³

The Second Phase (January 1942-May 1943)

This optimism proved to be misplaced; the Atlantic battle took a serious turn for the worse in 1942. But even as shipping losses climbed to alarming levels, Churchill rejected many of the Admiralty’s proposed solutions.

The main point of contention was the allocation of long-range aircraft. Naval leaders called repeatedly for a major expansion of RAF Coastal Command, which was responsible for supporting the Navy in the defense of shipping. They ran into determined resistance, however, from senior air force officers. They were committed to building up RAF Bomber Command to strike directly at Germany. In their view, protection of maritime communications was an inherently defensive task that should absorb as few resources as possible.

Churchill, always eager to take the war to the enemy, found the latter argument irresistible. The Admiralty’s urgent calls for aircraft were therefore denied or scaled back in favor of the bomber offensive. Depriving Coastal Command of long-range aircraft would inevitably mean heavier shipping losses. But this was a sacrifice Churchill was willing to make if it might hasten Germany’s defeat. “It might be true to say,” he told the War Cabinet in July 1942, “that the issue of the war depends on whether Hitler’s U-boat attack on Allied tonnage, or the increase and application of Allied Air power, reach their full fruition first.”⁴

Stroke and counter-stroke

Churchill felt confidence in the summer of 1942. Britain’s import situation was still not critical, and American shipbuilding was beginning to move into high gear. The U.S. would soon be producing enough new merchant shipping to replace British losses even at their heavy rate. “There is no reason,” Churchill informed his colleagues, “to assume that we cannot get through the present year or that the tonnage position in 1943 will not steadily improve.”⁵ If the import situation did worsen, he was confident that air resources could be allocated to avert disaster.

Within a few months, however, flaws began to appear in Churchill’s strategy. By autumn it was clear that Britain was not benefitting as expected from American ship construction. Over the course of 1942, shipping under British control decreased by around two million tons. The problem was that the new American-built merchant shipping was being snapped up by the American armed services. Unless something changed, Churchill’s advisors warned, Britain had virtually no chance of meeting its minimum import requirements in 1943.

With an import crisis on the horizon, Churchill decided in November that he must once more take an active role in the Atlantic battle. His first step was to begin lobbying Washington for a larger share of its new merchant ship construction. The second was to resurrect the Battle of the Atlantic Committee, now renamed the Anti-U-Boat Warfare Committee. This body, like its predecessor, brought together various departments with a stake in the Atlantic battle. Its job was to identify and expedite measures to reduce losses at sea. Churchill himself had no strong views on how to accomplish this. But diverting long-range aircraft from the bomber offensive, he warned, was not one of the options.

Naval proposals

The Naval Staff used the Anti-U-Boat Warfare Committee to advance their own ideas. Admiral Sir Dudley Pound, the First Sea Lord, explained that the heaviest shipping losses were incurred south of Greenland. This stretch of the North Atlantic convoy routes was so far from Allied bases that convoys seldom received air cover during this stage of their journey. German U-boats operated in “wolf packs” in this area, known as the “air gap.” They could maneuver on the surface with little fear of detection or air attack, which greatly increased their effectiveness.

To fill this critical hole in defenses, the Admiralty wanted land-based aircraft with an exceptional range of around 2500 miles. That was significantly more than regular “long-range” aircraft could manage. Fortunately, a solution was at hand in the American-built B-24 Liberator bomber. With extensive modifications, these aircraft could achieve the “very-long range” (VLR) needed to support convoys traversing the “air gap.” Neither Churchill nor the RAF had any reason to object to the diversion of Liberators to the Battle of the Atlantic. The bomber was considered unsuitable for the night bombing of Germany, and Coastal Command already possessed an ample supply.

The conversion of Coastal Command’s B-24s to VLR capabilities was promptly assigned high priority. Alas the modification process was excruciatingly slow. If the Atlantic battle ever truly frightened Churchill, it would have been during the early months of 1943. His pleas for more American ships were at first unsuccessful, and U-boat war was going from bad to worse. In March alone, the Allies lost 120 merchant ships (around 700,000 tons). The only bright spot for Churchill was that Roosevelt agreed in March to increase Britain’s supply of new merchant ships.

The end of the beginning…

…in the Battle of the Atlantic was reached soon after. By the end of May 1943, the “air gap” had been finally closed. Convoys in these waters were now covered not just by the modified B-24s of Coastal Command, but also by VLR aircraft operated by the Royal Canadian Air Force from Newfoundland, and new British and American escort carriers deployed along the Atlantic trade routes. The dramatic reversal in the air situation coincided with the Allies’ renewed ability to read U-boat signals. The efficiency of aircraft and convoy escorts also improved.

All this finally swung the tactical balance at sea in favor of the Allies. Before May was over, Allied shipping losses had plummeted and U-boat losses had risen to the point that Grand-Admiral Dönitz, head of the German navy, was forced to suspend his operations in the North Atlantic.

This was not the end of the Battle of the Atlantic. U-boats continued to prey on Allied shipping right up to the end of the European war. But they never again posed a major threat to Britain’s war effort. The defensive victory at sea left Churchill free to focus once more on taking the war to the enemy.

Endnotes

¹ Winston S. Churchill, The Second World War (London: Cassell, 1948-1953), vol. V, p. 6.

² Ibid., vol, II, p. 529.

³ Ismay to Sir Charles Portal, 20 August 1941, ADM 205/8, The National Archives.

⁴ Churchill memorandum, “A Review of the War Position,” 21 July 1942, in Martin Gilbert, ed., The Churchill Documents, vol. 17 (Hillsdale, Mich.: Hillsdale College Press, 2014), 979-82.

⁵ Ibid.

See also Christopher M. Bell, “Did Churchill Prolong the Battle of the Atlantic?”

The author

Dr. Bell is Professor of History at Dalhousie University. His publications include Churchill and the Dardanelles, Churchill and Sea Power and (with co-editor Marcus Faulkner) Decision in the Atlantic: The Allies and the Longest Campaign of the Second World War.