Most books on the Atlantic campaign paint it as a near-run thing for the Allies. The reality was much different. The first six months of the Atlantic campaign were only a skirmish. Following the Norwegian campaign, the Germans again turned their attention to cutting off British trade. In June 1940, France surrendered. This changed the entire complexion of the campaign as now the U-boats had bases from Norway down through France. This gave the Germans a series of naval and air bases that directly threatened Britain. From the spring of 1940 until the spring of 1941, Britain was under the greatest threat of a German blockade.

However, the Germans lacked the plans and the assets to take advantage of this situation. Instead of mounting pointless terror raids against British cities, a concerted campaign against British ports would have been more impactful. In terms of naval resources, the Germans lacked the means to launch crippling attacks against British shipping. Germans surface raiders were not numerous enough to provide decisive results, and the operations of the Kriegsmarine’s heavy surface units, though spectacular when used against shipping, amounted to little more than pinpricks.

Had the Germans given the highest priority to U-boat construction at the onset of the war, decisive results might have been possible. Instead, this priority was only assigned in July 1940, which meant that new boats did not arrive in greater numbers until the middle of 1941. It also meant that the British had almost a full year to ramp up escort production. The delay in the increase of U-boat construction until after the British dramatically increased escort production was one of the main reason the U-boat offensive against Britain was defeated.

With the limited number of boats available, Admiral Karl Dönitz realized only minor success in the opening months of the campaign. By May 1940, sinkings from U-boat attacks in the Atlantic totalled 148 ships of 678,130 GRTs (gross registered tonnage). Even when additional shipping losses were added from mines and smaller U-boats in the inshore waters off Britain, the total attrition of shipping in no way posed a serious threat to Britain and its war effort. Compared to the losses caused by surface ships and mines, it was readily apparent to both the British and the Germans that U-boats posed the main threat to shipping. In 1939, the British merchant fleet reached 17,984,000 GRT. Given this, the scale of losses to date was insignificant. At this point, Allied construction of new ships was covering losses.

The U-boat threat grew in the second part of 1940. During the so-called ‘Happy Time’, U-boats accounted for an average of eight ships per month/per boat. A combination of little British intelligence on U-boats, inadequate air cover, few escorts, and rudimentary tactics and training made this possible. Only the fact that there were fewer than 30 U-boats at sea during this period saved the Allies from suffering truly crippling losses. However, this success was fleeting – by February 1941, the monthly average was down to two ships per month/per boat. From this point, Dönitz was forced to rely on mass attacks against convoys instead of relying on a small number of excellent commanders decimating poorly guarded convoys. In this book, and in every other account of the battle, only the convoys that came under attack are mentioned. The vast majority of convoys were not subjected to attack and thus their safe passages go unmentioned. This is borne out by the numbers. Between 1 January and 30 June 1941, 37 HX convoys set out for Britain with 1,413 ships. Of these, only 30 were lost – a loss rate of just over 2 per cent. Of the 91 HX convoys from late 1940 until the end of 1941, 79 were not attacked and suffered no losses. Even the slow 18 SC convoys suffered little – only 11 of 576 ships were lost, about the same rate of loss. Overall, from SC 8 until SC 62 at the end of 1941, 46 of 56 convoys suffered no losses at all. For the 19 SL convoys, 26 of 750 ships were sunk (over 3 per cent loss). Of the 340 ships in HG convoys, 10 were lost (3 per cent). Losses to westbound convoys were always lower. A total of 109 OB and OG convoys transited during this period; of the 3,307 ships, 33 were sunk for a loss rate of less than 1 per cent.

During the final six months of 1941, the Allies successfully defended their North Atlantic convoys. Escorts for HX convoys were the most successful – of 1,560 ships in 31 convoys, only two were damaged. As had been the case since their inception, the slow SC convoys were the most vulnerable. Of the 1,187 ships in 27 such convoys, 35 were lost. Even this represented only a 3 per cent loss rate. On a smaller scale, the 17 SL convoys suffered a proportionately greater loss rate of 4 per cent (15 ships sunk out of 359).

Losses to outbound convoys in the North Atlantic were historically lower, and this remained true in the second half of 1941. Of the 2,537 ships steaming in 60 OB and ON convoys, a mere three were sunk. Proportionally, the highest losses were suffered by the HG and OG convoys. In 11 such convoys with 509 ships, 32 were lost (just over 6 per cent). Finally, on 15 OS convoys, with 574 merchants, only eight were lost.

Though worldwide losses of merchant ships in 1941 totalled 1,299 ships (of which 833 were British), new construction in Britain and the addition of foreign-flagged ships meant that there was a net tonnage gain in Britain’s merchant fleet over the second half of 1941 of 249,000 tons. At the end of 1941, the size of Britain’s merchant fleet was larger than it had been at the start of the war. Including British flag ships and foreign flag ships under British control, 3,616 ships were available of some 20,693,000 tons. This fleet was able to import 44,586,000 tons into Britain in 1941. Though lower than pre-war levels, and low enough to force rationing of some items, this was sufficient to meet basic requirements. Germany’s plan to blockade Britain was failing.

By mid-November 1941, virtually all German naval operations in the North Atlantic ceased. The Allies used the second half respite in 1941 to good effect by reinforcing defences in the North Atlantic, which was always the most important area of the Atlantic campaign. By the end of 1941, the British appeared on the verge of victory. In December of that year, the US entered the war, making Britain’s long-term prospects excellent. Now the U-boats were facing the combined resources of the two largest maritime powers on the planet.

With an avalanche of British- and Canadian-built escorts reaching service, and an expanded Coastal Command, all underpinned by an excellent intelligence network, the odds against the U-boats were increasing. Britain was no longer fighting alone. Since May 1941, the US had been a virtual ally of Britain giving it enormous resources in the form of Lend-Lease and even escorting convoys in huge swaths of the Atlantic. In December 1941, with the US in the war on a formal basis, it became impossible for the Germans to achieve victory in the Atlantic.

Dönitz’s prospects for 1942 did not look promising. The favourable trend he did have was increased U-boat production, which by 1942 would provide him with the 300 boats he had stated in 1939 were necessary to win the campaign in the Atlantic. With this number of submarines, he might have the capability to find convoys and mass enough U-boats against them to overwhelm their defences. Before this theory could be tested, the American entry into the war provided Dönitz with an opportunity that he was quick to seize. A second Happy Time was on the horizon.

You can find out more in CAM 408 Battle of the Atlantic (1): The U-Boat Campaign against Britain, 1939–41