On the strategic level, the U-boat campaigns in the Atlantic were a continuation of the fighting in World War I. The Germans tried to use submarines to enforce a blockade of Britain, while the British and their allies made use of the convoy system to shepherd as much shipping to safety as possible. On both sides, technological advances had occurred, although this was more true during the war than in the two decades preceding it. Before 1943, changes in tactics proved much more influential than changes in technology. From 1940 to 1943, the German system of Rudeltaktik, or wolfpack tactics, did more than any other element to upset the naval balance of power in the Atlantic, bringing Britain closer to defeat than at any other time in either of the World Wars.
U-boat commanders in World War I, including Karl Dönitz, were drawn to the idea of bringing several submarines to bear against a given convoy. The convoy system, created in order to offer merchant shipping as much protection as possible against the threat posed by submarines, had the paradoxical effect of offering a target-rich environment to any submarines that managed to make an attack. Commanders who made such attacks and escaped counterattack by the escorts knew the frustration of letting dozens of valuable targets go after only having scored a handful of hits. A coordinated attack by a series of U-boats could have changed the outcome substantially, but in World War I, it was not possible to coordinate teams of U-boats at sea.
Radio technology had advanced substantially between the wars. In this way, it became possible to coordinate such teams after the outbreak of World War II. Moreover, in the person of Karl Dönitz, Commander in Chief of the U-boat arm, the German Navy had a strategist who was committed to exploiting this opportunity. Even so, it took some time before the system could be implemented. The first reason was purely quantitative: when the war began, Germany only had 56 U-boats, and eight of these were small craft, suitable only for coastal use and serving mainly in a training role. Teamwork could only proceed on a small scale. The other reason was logistical: German U-boats needed to pass through British waters (typically passing north of Scotland rather than moving through the English Channel) to reach their targets and again to return. This reduced the likelihood of successfully assembling a proper “wolfpack” and keeping it in position to strike convoys in the early period of the war.
The fall of France in June 1940 materially changed the circumstances for the German Navy. The entire Atlantic coast of France was held by the Germans as occupied territory, affording the Navy a number of ports suitable for tending U-boats. Brest, Lorient, St. Nazaire, La Rochelle and Bordeaux were the principal bases, and they became available in July of that year. At the simplest level, an increase in the number of bases meant an increase in the number of U-boats that could operate on the high seas at any time; this was also a time when the construction of U-boats grew by orders of magnitude. In 1939, 18 were built; in 1940, 50 new subs were made, and in 1941, 199 more. The submarine pens of western France would remain full for some time.
The new bases offered other advantages. They were much further to the west than the bases on the German coast, extending the range of U-boat operations much deeper into the Atlantic. Maintaining these bases reduced the risks attendant upon the passage of U-boats past Britain into the Atlantic; once a U-boat had gotten past British coastal waters once, it could return to France before resuming its efforts in the Atlantic. U-boats could leave French ports, travel west by northwest, and find themselves in the thick of the convoy lanes without having to take the risks of traveling too close to Britain. Finally, control of western France offered the prospect of aerial support for the U-boats, especially in the matter of reconnaissance, although it was far from certain that such aid was forthcoming. Because of Goering’s jealousy over anything connected with the Luftwaffe, it was not until 1941 that the Navy was granted the use of a squadron of reconnaissance planes.
On the British side, losses in the first half of 1940 contributed to the freedom with which the U-boat captains could operate in the second half of that year. The Royal Navy’s reserve of destroyers had suffered particularly badly during the Norwegian campaign and then again during the Dunkirk evacuation. Because of all of these factors, the U-boats enjoyed great successes in 1940. It was dubbed the “Happy Time,” and during this period, U-boat commanders and their superiors in port were able to develop wolfpack tactics in an increasingly organized fashion. The “Happy Time” ended early in 1941, due to the breaking of the German codes, but by the summer, the Germans had developed fairly standard practices for Rudeltaktik.
The first consideration of Rudeltaktik was the “pack” itself. A single pack was built, officially, around about fifteen U-boats. One representative pack is the Group West, which, in the summer of 1941, consisted of eleven Type VII U-boats and four Type IX U-boats. In practice, numbers varied for reasons such as battle losses, repairs, and the training of new crews and the outfitting of new vessels, but in principle, the discovery of a large convoy by aerial reconnaissance or by the luck of an individual U-boat was meant to initiate a process that gathered upwards of 15 U-boats into a single location, where they would simultaneously attack the convoy. The escorts would be overwhelmed by the number of attackers, and together, the submarines could inflict serious damage on the convoy.
To be effective, a wolfpack had to operate within a reliable patrol zone. The ocean was immense, and individual convoys could choose from a number of possible courses to arrive at Britain. Without effective patrols, U-boats might never encounter a convoy during the three weeks of their voyages. While the specific courses might vary, however, convoys were still traveling in identifiable transit lanes that moved roughly from west to east. The wolfpack system placed U-boats in courses that intersected these lanes at ninety-degree angles. The chance of any one U-boat making contact with a suitable convoy might be low, but with as many as fifteen submarines making comparable sweeps through the area, the chances increased substantially; aerial reconnaissance also contributed to the likelihood of spotting the target. Once a given U-boat found the convoy, the wolfpack system was activated.
The first submarine to detect the convoy followed it with discretion while maintaining regular radio contact with headquarters. Headquarters plotted the course of the convoy while directing the other U-boats of the wolfpack to it. When the number of available U-boats was considered sufficient (it did not need to be the full group of fifteen), the pack was allowed to make its attack. From that point, the attack was no longer coordinated; each submarine operated independently, following the best experience of its captain and crew, but multiple attacks at different places in the convoy were sufficient to challenge the best efforts of the escorts.
All options were available to the U-boat commanders, but generally, the best results came from attacks at night, made from the surface. U-boats were very slow underwater, but at the surface, the Type VII U-boats could approach 18 knots, which was twice the speed of many convoys, and sometimes proved faster than the escort vessels. This, combined with the U-boat’s low profile, permitted the infiltration of many convoys, allowing the officers to select the best available targets. Another tactic called for attacks from greater distances, but allowed the U-boat to fire a series of torpedoes at several targets, beginning with the furthest and ending with the closest. If done correctly, the torpedoes would all explode simultaneously, creating a great deal of chaos.
Under these circumstances, it was typical to break off the attack at dawn, although the pack might return on successive nights, especially when additional U-boats came into range. Sometimes it was necessary to fight while submerged, however, especially as the Allies developed better radar, which made infiltration harder to accomplish.
In the summer of 1941, Dönitz had 184 U-boats in his fleet, permitting the creation of ten separate wolfpacks; in practice, the available numbers were around 120. Production continued to rise, and the Germans had some 250 U-boats by the end of the year, when war with the United States began. American unpreparedness paved the way for another “Happy Time,” during which long-range U-boats (Type IX only) operated near the American coast and in the Caribbean. As the American Navy acclimated to the circumstances, and losses decreased, the U-boats changed their focus again to the center of the ocean, in an area where land-based aircraft from either shore could not follow. In mid to late 1942, about fifty U-boats were in this area on a constant basis, and at the beginning of 1943, this rose to 100. Allied losses rose to the point that they would have been unsustainable if they had continued for long.
The spring of 1943 brought another change in the balance of power. The Allies were able to increase the protection of air cover with longer-ranged aircraft, crowding the U-boats out of the most lucrative zones. Improvements in radar, sonar, and anti-submarine weaponry combined to make U-boat attacks more costly, and soon the submarine losses became high enough to bring an end to general operations in the Atlantic in May. The time of the wolfpack had ended.
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