The Battle of the Atlantic was the longest and most bitterly fought campaign of the war, a contest of courage and technology which claimed the lives of two-thirds of the Third Reich's U-boat crews. Yet when the crisis for the Allies came, in late 1942, the German navy was within an ace of winning what Admiral Donitz called 'a heroic fight which knows no equal'.
'THE ONLY thing that really frightened me in the war', disclosed Winston Churchill in his memoirs, 'was the U-boat peril. It did not take the form of flaring battles and glittering achievements. It manifested itself through statistics, diagrams and curves unknown to the nation, incomprehensible to the public'.
The most important of these statistics were the tonnage of Britain's essential imports and the rate at which Germany's U-boats could sink the ships in which they were brought to British harbours. In 1939 Britain produced only half the food its 50,000,000 people needed. The rest - particularly beef, lamb, pork and wheat - had to be shipped from Australasian and North and South American ports.
At the same time British industry, backbone of the second largest economy in the non-Communist world, was heavily dependent on imports for non-ferrous metals, much of its crude ores and chemicals, many of its machine tools and all its petroleum. In 1939 55,000,000 tons of imports were carried to the country by the world's biggest merchant fleet.
That merchant fleet consisted of 3,000 ocean-going vessels and about 1,000 large coasters manned by 160,000 seamen, almost all British nationals. To protect them in convoy - and the Admiralty decided to introduce a convoy system from the outset of the war - the Royal Navy had about 220 destroyers, many of them needed for fleet duty, and only 70 were specialised anti-submarine craft.
The latter were all equipped with asdic (sonar), the echo-sounding device which indicated the bearing of a submerged submarine and its range from the attacking escort (though only up to 1,000 yards). But asdic gave no indication of depth. This was a serious limitation, since the depth-charges used to attack submarines had to be fused to explode at the correct depth if they were to succeed in damaging their target.
Fortunately for the Royal Navy, Admiral Karl Donitz's U-boat fleet also operated under severe handicaps. Before the war Donitz had put forward a plan for the construction of 300 U-boats, arguing that with such a fleet he could starve Britain into surrender. But of the 57 built by 1939 only 30 were ocean-going types, and only six were at sea at any one time. Moreover, the location of Germany's U-boat bases in the Baltic and North Sea required the U-boat captains to make long sea passages around the north of Scotland before they could get among the transatlantic convoys.
For the first nine months of the war, therefore, the statistics Churchill feared were not too alarming. Donitz was building around five U-boats a month and losing three, and his captains were only managing a monthly hit rate of four merchant ships grossing 200,000 tons. The rate of construction of merchant ship replacements was lagging dangerously behind but the loss could be made good by chartering from neutrals. Meanwhile, the slow rate of expansion of the U-boat fleet meant that Donitz's aim of starving Britain into surrender was being brought no nearer.
The fall of France suddenly and terrifyingly transformed this picture. At a stroke the power of the U-boat fleet was multiplied many times by Germany's acquisition of the French Atlantic ports. No longer forced to make the long passage round Scotland, the boats could be among the convoys within two days of leaving port. And many more of them could be kept on patrol, because turn-round time was sharply reduced.
The change was immediately reflected in a dramatic rise in the rate of sinkings. In the next nine months of the war, from July 1940 to April 1941, the Merchant Navy lost 2,500,000 tons of shipping of which only 1,000,000 were replaced by new building. And U-boat construction increased. By early 1941 there were 113 in service.
This increase in numbers allowed him to institute the 'pack' tactics with which he had planned to win his battle long before the war began. Called 'wolf pack' tactics by the British, the pack system deployed U-boats in long patrol lines across the Atlantic convoy tracks. Their captains waited on the surface until a target was sighted, whereupon a short cipher transmitted by Donitz's headquarters at Kerneval in Brittany was enough to have the rest of the pack homing in on the target.
The U-boats then submerged until nightfall, when they surfaced for a mass attack on the merchantmen. Because the U-boats were at least as fast as the convoy escorts and almost always outnumbered them, these tactics proved extremely successful.
The Royal Navy fought back as best it could. It was aided by the United States Neutrality Act, passed on the outbreak of the war, which effectively warned Donitz off the western Atlantic. It was also assisted by RAF Coastal Command, which used such aircraft as could be spared from the bombing campaign to mount long-range patrols designed to spot U-boats and drive them below the surface.
In addition the navy was gradually building up its escort fleet, which totalled about 375 by 1941 with the inclusion of Belgian, Free French, Norwegian and Polish ships. Above all, it was fighting an intense radio war against its Intelligence Centre's opposite number, the German Navy's observation service, or B-Dienst.
The backroom war
There were many strands to the radio war. One was simple position fixing by the interception of enemy transmissions. Sighting and sinking reports were another. But at the heart of the war lay the great game of decryption, which pitted the B-Dienst against the British Code and Cipher School at Bletchley.
In every arena but one of the radio war Bletchley was superior to its German equivalents. The exception, critically, was at sea. The U-boats were scrupulous in their use of the key - codenamed Shark by the British - they used to encode messages on their Enigma cipher machines. The Royal Navy, for unjustifiable reasons, did not use a machine cipher but clung to a book code whose secret had been broken by the B-Dienst.
Throughout much of 1941-2 and well into 1943, therefore, the Germans were able to read the convoy traffic while the British were not regularly reading Donitz's instructions to his wolf packs. As a result, the wolf packs were regularly homing in on the convoys.
Germany's advantage in the radio war would soon have brought the Atlantic battle to a head had not the entry of the United States into the war in December 1941 tempted the U-boats away from the eastern and central ocean to the American coast. For various reasons the US Navy proved unable to institute a convoy system for several months, and the imposition of a blackout in coastal built-up areas was similarly delayed.
Consequently, U-boat captains were presented with a succession of individual ships silhouetted against shore illuminations, which constituted easy targets. So high was their rate of success in American waters in the first half of 1942 that they would give the period the nickname 'Happy Time'.
However, America's entry into the war reversed the material basis on which the Atlantic battle was being fought. Previously the British had just been able to make good their losses by drawing on the world's stock of neutral shipping to supplement the shortfall in their own replacement programme. But once American shipyards were added to the Allies' productive capacity, replacements began to appear faster than even a fleet of 300 U-boats could sink them.
This was partly because America's depressed shipbuilding industry had a lot of spare capacity. But the main reason was the creation of entirely new prefabrication plants. The Kaiser Organisation, which had no previous experience in the industry, conceived a method of mass-producing the 10,000-ton Liberty Ship, a standardised cargo carrier which could be launched in three months from scratch.
As a publicity stunt - one with terrifying implications for Germany - the "Robert E. Peary" was built and launched in four days and 15 hours in November 1942. By then American yards were completing three Liberty ships a day, together with substantial numbers of its tanker equivalent, the 14,000-ton T 10. By the end of the war a total of 2,700 Liberty ships had been launched. And since they were bigger and faster than their pre-war equivalents, the carrying of the transatlantic merchant fleet was increasing by an even greater rate than the excess of launchings over the sinkings alone would indicate.
In 1942, though, the outcome of the Battle of the Atlantic still hung in the balance. Surviving elements of the German surface force, the Scharnhorst, Gneisenau and Tirpitz, obliged the Admiralty to maintain a large fleet in home waters, including a precious aircraft carrier. Memories of the alarm caused by the escape of the Bismarck, destroyed after a chase which had engaged most of the navy's capital ships in May 1941, ensured that.
The Home Fleet had the additional duty of standing ready to protect convoys on the North Russia run, which were threatened by German surface ships and shore-based aircraft as well as U-boats. The shortage of aircraft, particularly long-range patrol bombers, meant that there was an 'air gap' in the mid-Atlantic, beyond the range of those based in Ireland, Iceland and Newfoundland, where U-boats could patrol in relative safety on the surface.
Escorts were still short, their sonar and radar equipment lacked range, and their active weapons, particularly the stern-dropped depth-charge, were not particularly effective. Above all, the U-boat fleet had grown to Donitz's target of 300.
It was in the nine months between July 1942 and April 1943 that the battle climaxed. And for many of those months the U-boats were in the ascendant. In November sinkings totalled 509,000 tons, a figure only exceeded once before during the 'Happy Time'. In December and January bad weather, which always broke up patrol lines, halved sinkings but in February 1943 120 U-boats sank 300,000 tons and the toll seemed set to rise.
Bletchley had broken the Shark key in December, and was helping the Admiralty Intelligence Centre to re-route convoys away from the established positions of wolf packs. But while not all the German signals were decoded, the B-Dienst was continuing to read the British Naval Cipher Number 3 through which the convoys were controlled.
During March there was a running battle involving two convoys codenamed HX229 and SC122 sailing from North American ports to Britain. The 40 U-boats engaged sank 22 of the 90 merchantmen and one of the 20 defending escorts while losing only one of their own number. 'Splendid', signalled Donitz to the three wolf packs, Attacker, Harrier and Robber Baron. 'More of the same'.
It seemed that the turning point of the Battle of the Atlantic had been reached and that German victory was in sight. Yet the signs were misleading. The turning point was indeed at hand, but the battle was about to go the Allies' way - for several reasons which Donitz had either failed to perceive or which had been concealed from him.
One reason was that Bletchley had achieved the ability to read the Shark key regularly and instantly. Another was that the Royal Navy finally abandoned its penetrated book code and adopted a secure machine cipher, thus depriving the B-Dienst of its intelligence of convoy movements. A third was a sudden surge in the number of escorts, which meant that convoys could be better protected and enabled 'support groups' to be rushed to the aid of convoys under attack.
But the final and decisive reason was that a true long-range patrol bomber, the B-24 Liberator, had come into convoy protection service. Able to remain airborne for up to 18 hours, the Liberator closed the mid-Atlantic air gap and denied the U-boats the ability to patrol in safety on the surface.
Another instrument of air power, the escort carrier, had appeared for close protection of the convoys. It carried up to 20 aircraft in a converted merchant hull, and no U-boat dared surface in its vicinity. Since a submerged U-boat could not catch even the slowest merchant ship, the wolf packs could no longer manoeuvre into attacking positions and so found their teeth drawn.
In May 1943 U-boat losses reached 43, which was far more than the Germans could replace. By then, too, the Allied merchant fleet was bigger than it had been at the outbreak of the war, and still growing. Donitz accepted the implication and ordered his wolf packs to withdraw to home ports. As he conceded in his memoirs, 'We had lost the Battle of the Atlantic'.
The U-boat war was not over, however. The German navy was experimenting with submarines which did not need to surface in order to reach an attacking position: an air-breathing submersible and a revolutionary hydrogen-peroxide design which needed no external source of energy. The latter was not perfected until the very end of the war and took no part in operations. But the former, which drew in air through a snorkel tube, made a trial cruise in May 1944.
Had the Atlantic ports not fallen to the Americans shortly afterward, its successors could have reopened the Battle of the Atlantic and caused the Allied navies the gravest difficulties in keeping the supply lines open. As it was, snorkel-equipped boats operated in northern waters until the end of the war.
When Donitz's crews finally surrendered in May 1945, they did so with their morale intact. For all the cruelties they had inflicted themselves, no group had suffered worse in the Battle of the Atlantic. Of 830 U-boats despatched on operations between 1939 and 1945, 696 had been lost. In the process 25,870 - 63 per cent - of their 40,900 sailors had been killed, easily the highest casualty rate suffered by any fighting branch in any service of any combatant country, was not short of heroism.
Taken from John Keegan's History of the Second World War, Part One: The Blitzkrieg Storm Breaks, published with The Daily Telegraph, August 29, 1989.
