German submarine use during the Second World War was largely an extension of the policies of the First World War. In both wars, there were notable examples of lone submarines sinking capital ships; perhaps the most dramatic case in the Second World War was when Günther Prien succeeded in sinking the battleship Royal Oak in the apparent safety of Scapa Flow in October 1939. Such successes, as well as failed efforts, were relatively few in both wars, however. The Royal Navy was too large and too well organized for the Germans to hope to seize overall naval superiority through the use of “David and Goliath” tactics. Instead, submarines were used primarily to attack British lines of supply despite the overall superiority of British naval forces.
In theory, the job of the U-Boat was to enforce a counterblockade of Great Britain, which of course was blockading Germany with its surface fleet. The primary difference between these two blockades is that the submarine has no way of detaining a boat carrying supplies through the threat of force; a submarine can only shoot, or not. Consequently, the success of a U-Boat was generally measured in the tonnage sunk. It was not merely a question of the number of boats that were sunk, but rather, of the amount of supply that failed to arrive in Britain because of the U-Boat.
The submarines of the Second World War had become significantly more sophisticated than their First World War equivalents, in part because experienced submariners like Karl Dönitz oversaw most of the prewar and wartime submarine development. At the same time, German U-Boats faced a gradual stiffening of resistance, with the refinement of First World War convoy tactics being supplemented with technological developments, such as air reconnaissance and attack, sonar, and the cracking of the German naval code. As the war approached its end, the balance had swung heavily in favor of the convoys, and the last, potentially game-changing, developments in submarine technology had appeared too late to have any effect.
The Battle of the Atlantic
Germany began the war with only a very small submarine force. Under the terms of the Treaty of Versailles, Germany was forbidden to build submarines at all, but even before Hitler came to power the German government found ways to carry on submarine research, such as by creating a dummy corporation in Holland. After Hitler came to power, all pretense was dropped. Work soon began on developing a long-range subs, the Type VII; just as importantly, a tightly-screened cadre of elite sailors began an arduous training program. As the Navy took delivery of the new Type VII subs, this training included ocean maneuvers that, among other things, experimented with an early form of wolfpack tactics: a sub spotting a convoy would signal others, and consequently a small group of U-Boats would arrive to attack the convoy from multiple directions. Such a tactic would increase the amount of tonnage sunk while spreading out the enemy’s defensive measures. Two boats even had the chance to experience combat during the Spanish Civil War.
When England declared war on Germany over the invasion of Poland, the U-Boats were activated. They numbered only 56, however, and some of those were already obsolete. Despite some technical difficulties, especially torpedo failure, they were fairly successful. U-boats generally patrolled the seas just west of the British Isles, attacking by day without fully surfacing. Once the submarine had struck, however, it often found itself under attack by sonar-equipped vessels, and for a short time the U-Boats were marginalized by being left hunting only solitary targets.
Each month, however, more U-Boats were released. Moreover, the conquest of France in May 1940 changed the terms of their deployment by opening up bases on the Atlantic coast. This allowed submarines to operate far deeper in the Atlantic, forcing the British to spread out their countermeasures. Moreover, fears of a German invasion brought much of the Royal Navy’s efforts to defense against an invasion fleet, further depleting the reserves used to hunt submarines. The occupation of France also provided airbases, and the Germans could begin to use airplanes to seek out targets in the Atlantic. The U-Boats also shifted their tactics, making their attacks at night, and for a while this brought high rewards. Finally, this combination of elements allowed the Germans to begin to utilize the wolfpack tactics tested before the war, although in 1940 numbers never permitted their wholesale use. At any one time, only 15 U-Boats were active, and fewer than 70 were available to the entire Navy.
Even with just a skeletal force, Germany was inflicting painful damage to Britain’s war economy. In 1941 it became clear that no German invasion of England was forthcoming, and naval resources were being redirected to the protection of convoys. Late in the spring, the British had managed to capture an Enigma coding device from a damaged U-Boat, allowing the Admiralty to decode German radio transmissions. The Germans began losing their most experienced crews, with only green recruits to replace them. Not only subs were being sunk, but also refueling tankers that made possible the wide dispersal of U-Boats through the Atlantic.
At the same time, German efforts were still increasing. By the end of 1941, the U-Boat force had grown to 250, and as many as 36 lurked in the approaches to England at any one time. When war with the United States came in December, the U-Boats began to attack targets in American waters. In the first half of 1942, the U-Boats enjoyed a great deal of success, but the US Navy gradually became used to fighting submarines, and with the combined efforts of the Americans and the British, the Germans were unable to build and deploy enough subs to push the battle in their favor. It was becoming difficult to coordinate enough subs in a given area to make an effective wolfpack attack.
From the middle of 1943 on, U-Boats were largely on the defensive, trying to remain militarily relevant in the face of a growing threat from the air. The U-Boats tended to cluster in the waters around southern England, while new radar devices and marginally more effective antiaircraft guns were used in the hope of giving the submarine more of a chance against air attacks. Such measures could not match the developments of the Allies, and in March of 1944 coordinated U-Boat attacks were suspended. Even limited efforts proved largely suicidal, and an attempt to stem the flow of troops from England into the Normandy beachhead was overwhelmed.
Research and development continued until the very end, but much like German aviation achievements, successes came too late in the war to have any effect on the outcome. Had the war continued, the new Type XXI submarines, as well as the Snorkel devices that permitted older subs to remain submerged, might have had some effect, but in the event they were irrelevant.
The German Navy lost its portion of the war as surely as Germany itself did. To a great extent, this loss was the result of a growing disparity between Germany and the Western Allies in technological development and economic power. At the same time, some measure of arrogance did enter the equation, as the Germans could not bring themselves to believe that it was possible for the Allies to have broken the Enigma code. This failure in particular turned a major setback into a decisive disadvantage.
At the same time, the U-Boat arm was able to accomplish some remarkable achievements. The U-Boat war was always a question of numbers, and while the numbers do vary from source to source, the general figures are still staggering. Roughly 2800 Allied ships were sunk by U-Boats in the Second World War, with a total tonnage well in excess of 14 million. More than 1100 U-Boats were built by the Germans, of which around 750 were lost. Perhaps the most telling sign of the short-lived successes of the German submarines lies in the nightmare vision they created in the minds of their opponents. Winston Churchill famously said that the only part of the war that really kept him up at night was the submarine threat to England’s lifeline.
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