On 3rd September 1939, the same day as war had been declared, the torpedoing by a German submarine of the British ocean liner, the Athenian. It marked the beginning of the Battle of the Atlantic which would not end until 8th May 1945. It had become a battle on several fronts spread over the Atlantic Ocean. The German surface fleet turned out to be relatively weak compared with the Royal Navy. It meant that the weight on any campaign against Allied shipping would inevitably have to be borne by vessels easily able to evade visual detection: the U-boats.
During World War II, the Battle of the Atlantic campaign began when the geographical constrictions of vessels operating only from German ports were overcome with the conquest of Norway, France and the Low Countries in 1940. This caused the German Naval High Command to conclude that a chance now existed for the German Navy to win the war. It would be by severing Britain’s vital maritime communications. This became the first phase of the Battle of the Atlantic. However, in 1940-41 it had proved a failure.
The vulnerability of single surface raiders to British squadrons, had become evident with the destruction of the pocket battleship Admiral Graf Spee in 1939. It had demonstrated conclusively with the sinking of the battleship Bismarck in May 1941. As for the U-boats, there were only about 20 available over the winter of 1940-41. The U-boat fleet commander, Vice-Admiral Karl Donitz calculated 300 would be necessary for absolute success.
Allied convoys attacked during Battle of the Atlantic
Nevertheless the U-boats that had become operational at this time scored some successes through innovative ‘Wolf Pack’ tactics. Patrol lines became established in the Atlantic to maximise the chances of spotting a merchant convoy. Once a U-boat or a long range reconnaissance aircraft had made visual contact. The other U-boats were informed by radio, they would converge on the convoy being trailed.
The wolf pack used darkness and numbers to confuse the few defending escort vessels before the moment arrived to fire torpedoes. Under optimum conditions the results could be devastating. Two eastbound convoys in late October 1940 had lost a total of 33 out of 79 merchant ships.
Though the establishment of an escort base in Iceland and Newfoundland helped extend the range of escort vessels and air cover. The US navy (USN) escorts took up some of the strain in the Western Atlantic in the autumn of 1941. Royal Navy and Royal Canadian (RCN) destroyers and corvettes were not numerous enough. They lacked an effective radar capable of spotting surfaced U-boats beyond visual range. However, the small size of the U-boat fleet in 1940-41, meant that shipping tonnage sunk could be made up through new construction.
Increase of U-Boats in the Atlantic
1942 began well for the U-boats. A flawed USN policy of aggressive patrolling and no inshore convoys gave the submarines easy pickings along the American coast. It would be until the policy become abandoned in the summer. Moreover, in 1942 the number of U-boats being built exceeded sinkings, the reverse was true of British shipbuilding. German signals intelligence was having more success than the British in anticipating enemy movements.
Convoys, especially slow convoys, became easier targets. In November 1942 over 725,000 tons of Allied shipping had been sunk; a figure which, if it could be sustained, Donitz calculated would cut the Allied lifeline across the Atlantic. The huge shipbuilding capacity of the United States made this a dubious assumption. There was no doubt that in 1942-43 U-boats were doing harm to Allied efforts to build up strength in England for operations in Europe.
In March 1943 a new low become reached when two eastbound convoys without enough escorts became savaged by a pack of 40 U-boats. 23 out of 92 merchant ships became lost at the cost of a single U-boat.
1943 looked to be a good year for the submarine campaign. If only in seriously delaying the build up for the cross-Channel invasion. In fact 1943 turned out to be the year of decisive defeat for the U-boats. Even with 60 U-boats operating in the Atlantic by the spring of 1943.
High-frequency direction-finding
A greater number of escorts, new technology, and greater co-ordination, coupled with huge merchant tonnage the USA would build, brought about defeat.
Success in decoding enemy signals had become by now about evenly split between the British and the Germans. In actual battle, the U-boats began to suffer serious looses. New centimetric radar, mounted on very long-range aircraft, with many also by now equipped with a powerful searchlight. An increasing number of surface escort vessels, made surfaced U-boats much more vulnerable to detection.
Pre-emptive attack both day and night, with high-frequency direction finding equipment (HF/DF). It allowed escorts to locate U-boats when they sent radio signals. Forward-fired depth charges also allowed escort vessels to maintain sonar contact during attacks on submerged U-boats. The strength of convoy air cover became increased through the deployment of small new escort aircraft carriers.
Many of these improvements dated from the latter part of 1942 or even earlier. It was only in the summer of 1943 that experience in their use and the full range of improvements began to tell decisively.
U-Boats declining during Battle of the Atlantic
Though plenty of merchant ships had been sunk, the U-boats suddenly began to disappear in large numbers. The hunter themselves had become among the hunted. No less than 33 U-boats had become sunk by the British, Canadians, and Americans in May 1943, mostly in the North Atlantic.
Donitz switched his emphasis to the mid-Atlantic, only to find the USN ready and waiting. In July 1943, twenty-two more U-boats had become sunk by USN air and surface escorts. The monthly tonnage of merchant shipping declined to five figure totals. A loss rate that was more than made up for by the massive increase in US merchant shipping production.
Though U-boats continued to operate and sink ships until the last days of the war. They no longer posed a threat to either British survival or the Allied capacity to mount operations against Europe from England. Allied success on land and in the air meant that the new types of U-boat (that might have reversed the balance in favour of the submariners) did not arrive in time.
The U-boat campaign, ultimately failed either to bring Britain to its knees or seriously impede the arrival of men and material from North America needed to carry the war to the Continent. That in turn meant that by 1943-44 the Wehrmacht had to face the prospect of invasion from the West. This was at a time when its fortunes on the Eastern Front were going from bad to worse. The Battle of the Atlantic had come to an end.