Why the Allies Won

by Richard Overy

  The development of effective Air to Surface Vessel (ASV) radar played a key part in the Battle of the Atlantic. A radar using wavelengths of 1.7 metres was developed, capable of detecting a surfaced submarine at 5 miles. The radar allowed aircraft to find submarines by day or night, but about a mile from the target their exact location disappeared on the screen because of distortion from the sea. By day visual contact could be maintained, but at night, when submarines cruised on the surface confident of invisibility, they were almost impossible to find. The solution emerged almost by accident. A junior RAF officer, Sir Humphrey de Vere Leigh, privately developed the idea of a powerful marine searchlight, located in the nose or under the wing of anti-submarine aircraft, which could be switched on at the point where the radar picture faded. The device was developed in defiance of orders from above, but its advantages became evident and it was accepted as a tactical experiment. During 1942 the Leigh Light was turned rapidly into an operational instrument. Flying dangerously close to the surface of the sea, the attacking aircraft tracked the target with ASV radar, until approximately 1 mile away from it an operator floodlit the area ahead. The aircraft then dived to 50 feet to deliver a pattern of depth-charges. The first successful attack was carried out on the startled crew of u-502 cruising in the Bay of Biscay on 5 July 1942. U-boat sinkings in July were four times as many as those in June. By August U-boats were forced to travel submerged and at night when they crossed the Bay to and from their bases; or they would move during daylight hours, with anxious look-outs scanning the skies for RAF patrols. But two months later the pendulum swung back the other way. German scientists rapidly developed a receiver set, ‘Metox’, which gave warning of aircraft approaching using the 1.7-metre frequency. The ball was back in the Allies’ court, to find a radar with greater accuracy and beyond submarine detection.60

  Ships suffered from the same deficiency as aircraft in the accurate location of submarines. Here too radar was the only answer. The standard long-wave 1.7-metre radar was of little use for tracking surface vessels, for there was too much activity from the sea itself, even in relatively calm weather. In 1941 the British navy sponsored the search for much narrower wavelengths. At Birmingham University the breakthrough was made. The invention of the cavity magnetron permitted the development of radio valves that could operate on much shorter frequencies, of 10 centimetres. When a radar set was built around the new valve it proved able to detect even a submarine periscope. The new Type 271 sets were installed on escort vessels from the middle of 1941. They did not yet work perfectly. The valves had a small power output until the development later in the war of the ‘strapped’ magnetron, the CV56 valve, which powered the radar sets of all naval vessels by 1943.61 In rough seas even this more sensitive radar was deceived by the waves. But centimetric radar gave a solid scientific foundation to the war at sea. Its constant refinement enabled more and more escort vessels to see in the dark around their threatened convoys.

  By 1943 all British and American vessels were fitted with some basic form of centimetric radar. Once the target was in range it could be destroyed either with gunfire or depth charges. During 1942 this technology was also improved. Instead of depth charges being dropped from the back of the vessel at the point where contact with the submarine through radar or asdic was lost, a new method was devised by the British Department of Miscellaneous Weapons Development. A multiple mortar, nicknamed ‘Hedgehog’, was installed at the front of the ship. It fired 24 small bombs, which fanned out in front of the ship and dived swiftly into the sea 200 yards ahead. The bombs were fitted with contact fuses, so that only a submarine hit would produce an explosion. The remaining bombs sank to the bottom of the sea. For sailors used to the climactic roar of the depth charges the new weapon was a disappointment; but it claimed fifty submarine kills by the end of the war.62

  Despite all these innovations the rate of sinkings hardly abated. It might well be objected that the painstaking organisation of sound intelligence, and the slow conquest of the scientific frontier made little difference to the Atlantic Battle. But the statistics deceive. During the latter half of 1942 there were many more submarines available to Dönitz, but their sphere of action was restricted more and more to the poorly defended areas in the mid-Atlantic, or the coast of southern Africa. Each U-boat in the Atlantic sank the equivalent of 920 tons per day in October 1940; in August 1942 the figure was only 149 tons, and in November 1942, even though the aggregate figure for tonnage sunk was the highest of the war in the Atlantic Gap, no more than 220 tons.63 The ratio of operational submarines to successful sinkings declined sharply over 1942. Allied efforts did not halt the submarine offensive, but in 1942 they prevented the carnage at sea from being very much worse. Merchant losses were still unacceptably high but the rate of loss was slowed down and contained, while the losses of U-boats rose steadily. During the second half of 1942 65 were sunk, four or five times the number lost in the first months of the year.

  There were other solid achievements for Allied naval power. In the Mediterranean, too, the careful application of air power, and the use of radar and radio intelligence, turned the tide. The convoys began to move through the areas of greatest danger with more success. Supplies were run to Malta, which became a front-line base in the fight against Axis aviation and shipping. During the course of the year the Royal Navy used the submarine weapon against the Italian fleet, cutting vital supplies to Axis land forces stretched out along the sandy supply lines to the Egyptian frontier. Two-thirds of Italy’s merchant marine ended up at the bottom of the sea, a quarter sunk by British submarines, 37 per cent by Allied aircraft. The Axis forces in North Africa were denied almost half their supplies, and over two-thirds of their oil.64 Pushed to their logistical limit against an enemy reinforced by supplies brought via the long sea route around the Cape, Italian armies, supported by Field Marshal Rommel’s small Afrika Korps, were finally pushed back at El Alamein in early November. Between November and May 1943, when Axis forces finally surrendered in Tunisia, Italian vessels plied the seas between Sicily and Tunis through a hail of Allied bombs, torpedoes and mines. Sailors called it the Death Route, for there was almost no chance of survival. Between November and May, in rough winter seas, beset by squalls and fog and pursued by the relentless drone of enemy aircraft, 243 ships were sunk and 242 damaged passing through precarious narrow channels cut across the minefields, each one 40 miles long and at some points less than a mile wide.65

  The U-boat threat was also contained sufficiently to permit the transport of troops and equipment across the Atlantic for operation Torch. The effort disrupted the normal flow of traffic but the naval build-up was successfully concealed from the enemy. The passenger liners Queen Mary and Queen Elizabeth scurried at high speed and in isolation across the Atlantic carrying fifteen thousand troops apiece. In October a vast convoy of 102 ships sailed from America bound for Casablanca, where 25,000 troops were to disembark. From the Clyde in Scotland sailed six assault convoys and six slower supply convoys, a total in all of 334 ships. The effectiveness of the convoy when it had adequate air protection and the benefits of modern technology was demonstrated beyond dispute. Only one small supply vessel was lost out of the whole armada. On 8 November, supported by heavy fire from the big battleships, Allied troops landed at Casablanca, Oran and Algiers. Local French troops soon abandoned the struggle and the combined Anglo-American force joined up with British Commonwealth armies chasing the Axis westwards from Libya. Although the final Allied victory was much slower and more costly than expected, German and Italian troops were bottled up by western naval and air power, fighting until there was nothing left with which to fight.66 On 13 May 150,000 Italians and Germans surrendered.

  The war in the Mediterranean did nothing to solve the U-boat war. At the end of 1942 the Battle of the Atlantic was delicately poised. Allied shipping was still dangerously vulnerable; the morale of the merchant mariners was low and casualties high. But U-boat losses were rising too, and German submariners were fac
ed with the stark reality that they would now survive no more than two or three sorties at most. Between January and May the Battle of the Atlantic reached its climax.

  * * *

  Nature itself supplied a backdrop to the crescendo of battle that was straight out of Wagner. The weather in the winter was never good; over the winter months of 1942–3 it was atrocious. Gale force winds for weeks on end drove the sea into icy mountains and valleys that could barely be navigated by submarine or victim. Driving blizzards made the sighting of vessels almost impossible. On the bridge of the submarine the men on watch were strapped down with strong security belts as the waves swept up and over the boat time after time. It was difficult to hold the wolf-packs together in pursuit of the convoys. In January 1943 only nine ships were sunk in the North Atlantic.

  The respite was only temporary. Hitler, determined to press home the submarine campaign at all costs, sacked Raeder and appointed Dönitz Commander-in-Chief of the navy. All resources for the naval war were concentrated on the production of submarines and the training of their crews. The B-Dienst continued to supply a stream of decoded messages alerting the submarine groups to the convoy routes. More U-boats than ever before were available to cover the Altantic Gap, an average of a hundred or more each day.

  On the Allied side there was the same sense of imminent climax. Meeting in January the Combined Chiefs-of-Staff agreed that the defeat of the U-boat was still their strategic priority, ‘a first charge on the resources of the United Nations’. More escorts and aircraft were sent to shelter the convoys. In London the U-boat war was placed under the direction of a remarkable British submariner, Admiral Sir Max Horton. In November 1942 he was appointed Commander-in-Chief of the Western Approaches. His brief was to find some way to reverse the downward slide in the anti-submarine war. He was a pugnacious, hard-working commander, chosen deliberately as a breath of fresh air in the campaign. He was respected rather than liked, ‘quite ruthless and quite selfish’ according to one of his staff. He kept unusual hours and expected his colleagues to do likewise. He worked in the morning, then played a leisurely round of golf every day between two and six, finally returning to the submarine plot room where he worked until well past midnight every night, gulping pints of barley water, barking at his subordinates and displaying what one witness described as an ‘uncanny prevision of what the enemy would do next’.67 As a former submarine commander he understood more clearly than his predecessors how Dönitz might react. He could also see clearly the weaknesses still evident in the Allied anti-submarine campaign.

  With the arrival of Horton to duel with Dönitz came the changes that would eventually tilt the Battle of the Atlantic the Allies’ way. He campaigned immediately for more aircraft, particularly long-range aircraft to fill the Atlantic Gap. He insisted that all aircraft hunting submarines at night should be fitted with Leigh Lights and centimetric radar. He set about reorganising the whole escort system, insisting on employing more up-to-date ships and escort carriers, and on the establishment of ‘support groups’ of submarine hunter-killers which could be moved quickly about the Atlantic battlefield to the point of greatest danger. He insisted on higher standards of training and preparation. During 1942 escort commanders and crews received only two weeks’ training for convoy work, and often entered the fray quite unequal to the task assigned to them. Horton appointed an officer to the task of training escort crews at greater length in the skills they needed, emphasising above all the ability to cooperate as a naval team, coordinating both attacks on submarines and the sheltering of their vulnerable charges.68 All of this took time; the initiatives of late 1942 flowered only with the passing months. Until they bore fruit Horton fought Dönitz with the weapons he had to hand.

  From the end of January, when the worst of the weather was past, were fought the fiercest battles of the Atlantic campaign. The first blows were struck against convoys HX224 and SC118 on route from America laden with goods for the Soviet Union. Contact was made by U-456, whose captain called up other U-boats and then moved in and sank three ships in strong gale-force winds. Dönitz stationed a wolf-pack in the Gap codenamed ‘Pfeil (Arrow). HX224 was hounded, although for little additional loss, but SC118, following two days behind, ran full tilt into the waiting submarine trap. Though the convoy had an unusually heavy air and sea escort, the submarines, pressing home their torpedo attacks at night against fierce counter-attacks, succeeded in sinking thirteen ships for the loss of three U-boats and severe damage to four more.69 At the end of February the submarines mauled three convoys going the other way. One of them, convoy ON166, was betrayed by radio intelligence and ran into a waiting wolf-pack. The ensuing battle stretched out over 1,000 miles of ocean and lasted four days. Ultimately two U-boats were lost but fourteen merchantmen were sunk. In London and Washington there was consternation. Even with improved escorts and air cover the convoys were still vulnerable. More worrying still, not even the fact that the British cipher school had succeeded at last in breaking into the Triton cipher prevented convoys from running into disaster. Messages could not always be decoded either fully or quickly though sufficient could be gleaned to permit the convoys to be re-routed. But the new routes could be detected by German intelligence, and so numerous were the submarines hidden in the Atlantic Gap that even the best-informed of convoys ran the risk of making accidental contact.70

  In March the worst fears were realised. The slow convoy SC121 crossing from west to east lost thirteen ships, with no loss to the submarine pack. Then on 5 March a large slow convoy of fifty vessels, SC122, escorted by three Canadian corvettes and a minesweeper, set off from New York. Three days later a faster convoy, HX229, left from the same port with 41 ships and an escort of two destroyers and two corvettes, following almost the same route as the convoy in front of it. In the mid-Atlantic the two convoys piled up one behind the other, presenting a large and tempting target. Forewarned of the convoy routes by German intercepts, Dönitz stationed three large wolf-packs, ‘Raubgraf’, ‘Stürmer’ and ‘Dränger’, across their path. Once more the weather deteriorated, with heavy seas, fog, and intermittent flurries of fierce snow and hail. Through these miserable elements the two convoys plunged until sighted by the 38 U-boats waiting for them. With no air cover in the heart of the gap, but with increased naval escort, the battle commenced. The first victim was HX229, which was sighted by U-653 on her way to refuel. The submarine dived as the whole convoy passed slowly above it. When it resurfaced the message went out to 21 of the waiting submarines to close and engage the convoy. During the night of 16–17 March, in high seas that hampered the use of shipborne radar, the attack was pressed home. Seven merchantmen were sunk or immobilised. During the course of the night the two convoys began to merge together, and in bright moonlight the U-boats now turned on SC122. Over the course of the day five more ships were sunk, but that morning for the first time very-long-range (VLR) aircraft arrived over the convoys. Only three aircraft were sent, all converted B-24 Liberator bombers, and only two managed to find the convoys. These two could only stay with the ships for short periods before their fuel ran dangerously low. But the submarines were exceptionally cautious in their presence. The two ships sunk that day from convoy HX229 were lost in the interval between the departure of the first Liberator and the arrival of the next. Over the next two days isolated kills were made, but by 19 March the convoys were out of the gap and under air cover. It was only then that the single submarine kill of the whole battle was made, U-384, sunk by a B-17 Flying Fortress from Benbecula Island in the Outer Hebrides.71

  For the Allies the battle was a disaster: 21 ships totalling 141,000 tons were lost for the cost of just one U-boat. Even worse might have followed but for the renewed intervention of the elements. In late March a fierce hurricane blew across the mid-Atlantic, so severe that the U-boats could not manoeuvre or attack. Most were withdrawn back to base to refit and refuel after a month in which they had sunk in all waters 82 ships of almost 700,000 tons. Two more convoys were sighted and
attacked in March, but the submarine commanders noted for the first time strong air cover provided by escort carriers. They could not prevent sinkings, but they kept most of the U-boats at arm’s length. This was small consolation in the Admiralty after a disastrous month. The naval staff recorded later that the U-boats came ‘very near to disrupting communications between the New World and the Old’.72 In the prevailing gloom there was speculation that the convoy system itself might no longer be effective. If such were the case the prospects for mounting any kind of Allied assault on Europe were poor.

  Admiral Horton was undaunted by the crisis. A considerable number of convoys had sailed in March and been steered clear of U-boats altogether. Moreover the kill rate was rising: nineteen U-boats were sunk in February, the highest figure for any month of the war so far, and fifteen in March. Radio intercepts indicated a distinct lowering of morale among the submarine crews. Attrition worked both ways. Rather than halt the convoys Horton planned in April to lure the U-boats into battle in the hope of inflicting insupportable rates of loss. He insisted, and insistence was Horton’s hallmark, that the Royal Navy release naval vessels to form the nucleus of his new anti-submarine hit squads, the ‘support groups’. By the end of March he had his way. Five support groups made up of destroyers and including existing escort carriers were readied for action. The support groups were to keep in close contact with the convoys, to be called at a moment’s notice. Overhead Horton now had the air support he had asked for in December, including the VLR aircraft fitted with centimetric radar and Leigh Lights which could plug the Atlantic Gap. He ordered all anti-submarine aircraft to concentrate on destroying submarines either around the convoys or in the approaches to the U-boat bases in the Bay of Biscay.73