And then there was the enemy. While Germany’s capital ships commanded headlines and their sorties inflicted some injuries, Axis submarine and air forces represented a much graver long-term threat, and the men of both arms displayed courage and skill. U-boats achieved striking early successes, such as sinking the old battleship Royal Oak in Scapa Flow, and wreaking havoc upon vulnerable merchantmen. Churchill as First Sea Lord estimated that the introduction of convoying in 1939 was responsible for a 30 per cent fall in Britain’s imports. Merchant ships were obliged to waste weeks waiting for convoys to assemble. Once ocean-bound, they travelled painfully slowly, and were offloaded on arrival by a lethargic and sometimes obstructive British dock labour force. Many ships that carried commodities in peacetime had to be diverted to move troops and munitions across huge distances by circuitous routes, to avoid Axis air and submarine concentrations – for instance, almost all Egypt-bound cargoes travelled via the Cape of Good Hope. The voyage to Suez lengthened from 3,000 miles to 13,000, while a Bombay-bound ship made a passage of 11,000 miles against the pre-war 6,000.
Until 1943, the Royal Navy was desperately short of escorts and effective technology to hunt U-boats. The British sank twelve German submarines in 1940, and just three in the six months between September that year and March 1941; intelligence and skilful convoy routeing did more to frustrate Admiral Karl Dönitz than did anti-submarine escorts. The Royal Navy was slow to realise the vulnerability of merchantmen off the African coast, where in 1941–42 just two long-range Type IX U-boats achieved some spectacular destruction, partly because they maintained wireless silence and partly because few defensive resources were available. The British were grievously hampered by lack of air support. The RAF’s Coastal Command was short of planes; its long-range Sunderland flying boats suffered from crews’ poor navigational and depth-charging skills, together with technical problems that reduced their effort in 1941 to an average two sorties per aircraft a month. Meanwhile, until 1942 many of the Royal Navy’s destroyers remained committed to coastal defence of Britain.
In the course of the entire war, while 6.1 per cent of Allied shipping losses were inflicted by surface raiders and 6.5 per cent by mines, 13.4 per cent were caused by air attack and 70 per cent by U-boats. The British suffered their first severe blow in the autumn of 1940, when the slow eastbound Atlantic convoy SC7 lost twenty-one out of thirty ships, and twelve out of forty-nine in the fast HX79. Thereafter, the tempo of the undersea war rose steadily: during 1941, 3.6 million tons of British shipping were lost, 2.1 million of these to submarines. Churchill became deeply alarmed. His post-war assertion that the U-boats caused him greater anxiety than any other threat to Britain’s survival has powerfully influenced the historiography of the war. It is scarcely surprising that the prime minister was so troubled, when almost every week until May 1943 he received loss statistics that represented a shockingly steady, debilitating depletion of British transport capabilities.
But the submarine force commanded by Dönitz was weak. Germany’s pre-war industrial planning envisaged a fleet which achieved full war-fighting capability only in 1944. Naval construction was skewed by a focus on big ships: a hundred U-boats could have been built with the steel lavished on the Bismarck. On the eve of war, Admiral Erich Raeder, German naval C-in-C, wrote: ‘We are not in a position to play anything like an important part in the war against Britain’s commerce.’ Until June 1940, Dönitz did not anticipate waging a major campaign in the Atlantic, because he was denied means to do so; the small, short-range Type VII boats that dominated his armoury were designed to operate from German bases. Even when the strategic picture radically changed with Hitler’s seizure of Norway and of France’s Atlantic ports, the Kriegsmarine continued to build Type VIIs. Productivity in German shipyards, hampered by shortages of steel and skilled labour, and later by bombing, fell below British levels. U-boats remained technically primitive. Innovation – for instance, the 1944–45 Schnorkel underwater air-replenishment system – was not matched by reliability: the revolutionary Type XXI sailed on its first war patrol only on 30 April 1945.
Thus, Dönitz’s force lacked mass, range and quality. Just as the Luftwaffe in 1940–41 attempted to deal a knockout blow to Britain with wholly inadequate resources, so the U-boat arm lacked strength to accomplish the severance of the Atlantic link. Germany never built anything like enough submarines to make them a war-winning weapon. Dönitz calculated that he needed to sink 600,000 tons of British shipping a month to achieve a decisive victory, for which he required three hundred U-boats in commission to sustain a third of that number in operational areas. Yet only thirteen U-boats were on station in August 1940, falling to eight in January 1941, rising to twenty-one the following month. This small force inflicted impressive destruction: two million tons of British shipping were sunk between June 1940 and March 1941. But in the same period just seventy-two new U-boats were delivered, far short of the number Dönitz needed. They achieved their highest rate of productivity – measured by tonnage sunk per submarine at sea – in October 1940; thereafter, while many more boats were deployed, their pro-rata achievements diminished.
As the war developed, while the Allied navies grew apace in skill and professionalism, the quality and determination of U-boat crews declined. One by one Dönitz’s aces were killed or captured, and the men who replaced them were of lesser calibre. German torpedo technology was almost as flawed as that of the 1942–43 US Navy. Direction of the U-boat campaign was hampered by changing strategies and impulsive interventions by Hitler. German naval intelligence and grasp of Allied strategy, tactics and technology were chronically weak.
It is a remarkable and important statistic that 99 per cent of all ships which sailed from North America to Britain during the war years arrived safely. Even in the bad days of April 1941, for instance, 307 merchantmen sailed in convoy, of which only sixteen were sunk, together with a further eleven unescorted vessels. In June that year, 383 ships made the Atlantic passage, in convoys of which submarines attacked only one, sinking six ships, along with a further twenty-two unescorted merchantmen. In 1942, by far the most alarming year of the U-boat war, 609 ships were sunk in the North Atlantic, a total of some six million tons. So prodigious was American shipbuilding capacity, however, that in the same period the Allies launched 7.1 million tons of ships, increasing their available pool of thirty million tons.
Yet, as is the way of mankind, the Allies perceived most of the difficulties on their own side. While posterity knows that in 1942 the U-boats inflicted the utmost damage of which they were capable, and that thereafter the tide of the convoy war turned steadily against them, at the time Churchill and Roosevelt saw only a steeply rising graph of losses which, if it had continued, would have crippled the war effort. In 1942 British imports fell by five million tons, imposing severe strains on food and oil supplies – the latter were reduced by about 15 per cent, requiring the government to dip into its admittedly large strategic stockpiles. This was attributable less to Dönitz than to the diversion of two hundred ships from the Atlantic shuttle to open an Arctic supply line to Russia. Whatever the causes, however, Britain’s shrunken deliveries alarmed a nation with its back to the wall in many theatres and three dimensions.
Even when the US supplied Britain with a few B-24 Liberators – suitable for very-long-range conversion and thus ideal for Atlantic convoy support – initially the RAF chose to use most of them elsewhere. Sir Arthur Harris, 1942–45 C-in-C of Bomber Command, fiercely resisted the diversion of heavy aircraft to the convoy war: ‘It was a continual fight against the navy to stop them as usual pinching everything,’ said Harris, who disliked British sailors almost as much as he abhorred the Germans. ‘Half my energies were given to saving Bomber Command from the other services. The navy and army were always trying to belittle the work of the air force.’ The Atlantic ‘air gap’ – the area of ocean beyond range of land-based cover – remained the focus of U-boat activity until late 1943.
An average of just over one convoy a week each way