161: Never Enough Boats


U-boats in Scapa Flow! Wolfpacks on the prowl!



Hello everyone and welcome to History of the Second World War Episode 161 - The Early War at Sea Pt. 11 - Never Enough Boats. This week a big thank you goes out to Andrew for the donation and to bigfatboss, Dave, Bas, Damien, Yooperine, and John for supporting the podcast by becoming members, you can find out more about becoming a member over at historyofthesecondworldwar.com/members. During the first six weeks of the Second World War, even with their lack of numbers, the restrictive rules of engagement placed on them, and the efforts of the Royal Navy the German U-boats would sink 60 ships in the first six weeks of the war. These varied greatly in six, from small steamers all the way up to the German’s crowning achievement the aircraft carrier Courageous. But, this was only the beginning. During the last three months of 1939 there would be two important events that would have longer term impacts on the war at sea, the first was the attack by U-47 under the command of Günther Prien against the British fleet anchorage at Scapa Flow, the second were the first attempts at executing the German Wolfpack attacks. Both of these changes would occur in October before the weather in the northern Atlantic reached a point where further U-boat operations were more difficult and would be curtailed until the return of better weather in early 1940. This episode will look at these two actions, the changes that they caused, and then the state of the war against British trade at the end of 1939.

Scapa Flow was the fleet anchorage of the British Home Fleet in 1939, just as it had been during the First World War but from the very beginning of the war there would be efforts to find a way to attack the ships of the Royal Navy that called it home. A few episodes ago there was a discussion of how the attacks from the Luftwaffe would play a part in keeping the Royal Navy out of Scapa Flow, but another major reason for this change was the attack of U-47. Obviously the British knew that U-boats might try to get into Scapa Flow to launch an attack, and so they had taken efforts to reduce this possibility through static anti-submarine defenses. One of these defenses was in the form of blockships which limited the channels that were navigable for German vessels. The Germans of course knew that these defenses were in place, but that did not entirely deter them from the effort and so during September and October there were efforts to find out more about the defenses in the area. These reconnaissance was done by the Luftwaffe as well as a few smaller U-boats and they were able to find a weakness, with one of the channels not being fully blocked by blockships which might allow a U-boat to make its way in through Kirk Sound. With this weakness identified Dönitz selected Günther Prien and U-47 to make the attack on a night that coincided with new moon, which would result in maximum darkness on October 13th. Prien was briefed on his mission, given the information about Kirk Sound and the U-47 would be on its way. Throughout the journey the crew of the U-47 were not briefed, and all secret documents and the U-boat’s enigma machine had all been left behind in Germany due to the likely event that Prien would be either sunk or captured, both of which might result in the British gaining access to the U-boat in the confined area of Scapa Flow. Prien would announce to his crew that they were making their way into Scapa Flow only after they had arrived, and after they had been fed a very nice meal of veal cutlets. Then the U-47 made its way through a narrow opening in the blockships. The journey into Scapa Flow was slow, and would take several hours as the U-boat very slowly moved forward. When the U-47 reached the area of the anchorage that the Royal Navy used it would spot two ships, which Prien believed were the battleship Royal Oak and the battlecruiser Repulse. He was correct on one count, it was the Royal Oak, but the other ship was not the Repulse and was instead the seaplane transport ship Pegasus. Two torpedoes would be fired at the Royal Oak, with one torpedo fired at Pegasus, the fourth torpedo that was supposed to be on its way toward Pegasus misfired in the tube. Only one of these torpedoes would hit and it was one of the ones fired at Royal Oak. But instead of hitting anything vital the torpedo would simply explode on the Royal Oak’s forward anchor chain, cutting the chain and also causing some structural damage and blowing a hole in the side of the ship. The U-47 would then turn around and fire its stern torpedo while the bow tubes were reloaded, but the stern torpedo would not detonate, although it is unclear if it missed or was just another dud. Then, when the bow tubes were loaded again 3 more torpedoes were all fired at the Royal Oak, and this time all three of them would hit and all three of them would explode. The results were catastrophic. There were three major holes in the ship, one in the engine room and then two more closer to amidships just as worryingly a massive fire started in the magazines. It would take only 13 minutes for the Royal Oak to tip on its side and sink, with 833 men, out of a total crew of 1,200 losing their lives. By that time Prien and U-47 were already on their way back out of Scapa Flow having completed their task just over 2 hours after making their initial way into the British anchorage and just a few hours later they were back in the North Sea on their way back to Germany. It was a tremendous success, even if only one ship had actually been sunk, but Prien not exactly satisfied, writing in the ship’s log that it was “a pity that only one was destroyed”. When they arrived back in Germany the crew was flown to Berlin to meeting personally with Hitler, and Prien was awarded the Knight’s Cross of the Iron Cross the first member of the German submarine corps to receive the honor. Because of the risk of both air and submarine attack the Royal Navy would abandon Scapa Flow as a fleet anchorage until March 1940, when both the protections against further U-boat and air attacks had been increased. Forcing the Home Fleet to leave Scapa Flow at least reduced slightly the geographic advantage that the Royal Navy had in its efforts against German surface and U-boat actions, as Scapa Flow was perfectly positioned to project power into the entrances and exits of the North Sea.

One of the major benefits that the Kriegsmarine had in their efforts to interdict British trade was the fact that they could read much of the wireless communications that were occurring on the British side. The ability of German intelligence to read these messages actually dated all the way back to 1935 when, during the Abyssinian Crisis when Britain and Italy came close to war German codebreakers had finally solved the decryption of British codes. This was a major advantage, especially when it came to hunting convoys because it allowed the Kriegsmarine to keep tabs on many convoys and their escorts. This ability would become more powerful over the first months of the war as the convoys became more and more established and organized, making the information about their position and courses even more powerful. This allowed U-boats to be directed to intercept the convoys, partially offsetting the low number of U-boats available, and it also opened up new possibilities. The one that Dönitz wanted to try was the idea of vectoring a larger group of U-boats onto a single convoy. This concept would come to be known as the wolfpack, and the first time it would be tried was in October 1939. Dönitz waited until the middle of October for two reasons. The first was because on October 4th new rules of engagement were issued for all U-boat operations in the North Sea and Atlantic, the U-boats could sink on sight any ship that was sailing under blackout rules. These rules would be even further relaxed on October 17th when, under the orders of Hitler U-boats were allowed to attack any British or French merchant ship, except for passenger liners, at any time. The second reason was because he had to wait for enough U-boats to be available at one time, with six being available in mid-October. Three of these would be type-VIIBs, and 3 would be Type IXs. But several of these U-boats would run into problems almost immediately, and before the wolfpack had even really commenced its operations. For example, the U-40 would hit a mine as it tried to make a night time run through the English channel while on the surface. It would sink almost immediately after hitting the mine. The U-42 would spot a British merchant freighter, the Stonepool, and would choose to attack it with its deck gun instead of using a torpedo. But the Stonepool was not defenseless, and began firing back while radioing the submarine alarm over the radio. Two destroyers would quickly arrive on the scene and begin attack the U-42, using asdic to deliver a depth-charge attack which force the boat to surface, but only 17 men, including the captain Rolf Dau would make it out before the U-boat slipped under the waves. One of the other U-boats, the U-37 would miss the wolfpack action for a totally different problem, it found two neutral ships on the way to the rendezvous and this pulled it out of position. With the remaining boats orders were sent to target convoy KJF-3, which was inbound from Kingston, Jamaica. From the start there were coordination problems among the available U-boats, with two of them attacking the convoy completely independently. The good news is that they were quite successful, with the U-48 sinking 2 French ships totally 21,000 tons. The first attack on any convoy was always the easiest because all that the U-boat had to do was find its way past the escorts, then it would be faced with a nicely organized group of merchant ships that could be attacked. Generally U-boats would attack at night, on the surface, and then launch a full load of torpedoes immediately and with a variety of targets. This was due to the fact that as soon as the first torpedoes exploded the convoy would scatter. This would make make it easier to pick off stragglers, but a U-boat would never been in as good of a position to hit multiple targets at once as when the initial attack was launched. The U-45 would be the second to arrive to attack the convoy, and would be in the position of trying to chase down ships of the convoy as they dispersed. They would still be able to find and sink two ships, but only just in time. U-45 would not live to experience the glory of these actions though, because it was very quickly attacked by four British destroyers who were able to sink it. Overall, the first wolfpack attack was a failure, with the loss of 3 U-boats with a total of only 4 of the convoy’s ships sunk. Although of course only one of those losses was really due to actions against the convoy, and it is very likely that 2 of them would have happened regardless of the plans for the wolfpack. Another convoy would be attacked by the remaining boats, the U-47, U-46, and U-48. They would be able to intercept a convoy on its way from Gibraltar to the British home islands. During this action each of the three U-boats would be able to sink another ship, but they would attack far more, only to be foiled by another set of torpedo malfunctions. The captain of the U-46 would become so frustrated with the torpedo situation that he would break radio silence just to report that he had fired 7 torpedoes that had malfunctioned, either through exploding early or other problems. This report really brought the torpedo situation to a head, and finally Torpedo Directorate at the German Admiralty started to confess to some of the problems that were being experienced. The newest issue was that the torpedoes were often running about 6 and a half feet deeper than they should have been, a problem that was known to the directorate but which was not reported due to the belief that it did not matter for the magnetic detonated torpedoes because it still within the range where the magnetic pistols should fire. Of course, when this was combined with problems where the magnetic pistols were not always firing when they should, well it ended up in a lot of torpedoes that simply did not detonate at all. Solutions to these problems were all in the future. This would be the final combined attack of the first wolfpack, with the U-46 and U-48 returning to Germany due to the fact that they were low on fuel and torpedoes. The three major lessons that were learned with these first wolfpack actions were that there needed to be more coordination between the U-boats, coordination that began as soon as the first U-boat arrived at the convoy. In the future the first U-boat would be told that they should not attack, but instead to shadow the convoy, relaying it position via radio so that other U-boats could converge on its location. Then when all of the other boats arrived they should seek to all attack at one time, to completely overwhelm the convoy’s escorts and then to launch the largest possible attack at one time, before the convoy could scatter. There would also be a slight shift to the planning for the attacks, with the goal of launching them further to the west and int the open ocean, which would prove the U-boats more time to maneuver and then attack before the escorts were increased by the anti-submarine forces that were held close to the European destinations of the convoys. These would be good lessons, it would however be multiple months before any of the lessons could be applied simply due to the fact that it would take that long before enough U-boats could be collected together for another operation.

After the operations of October there would be a major diversion of U-boat resources in November to support Kriegsmarine surface operations. In late November there was a plan to send several German surface ships, including the small battleships Gneisenau and Scharnhorst on a sortie into the northern Atlantic, with one of the goals being to distract the Royal Navy from sending further resources into the South Atlantic to track down the Graf Spee. This kind of action by German surface vessels would almost certainly be met by a response from the Royal Navy and the hope was that U-boats would be pre-positioned to take advantage of this by being in the North Sea and intercepting the Royal Navy ships that were sent to meet the German surface group. The interceptions would fail, and it would cost one U-boat when the U-35 was spotted by a British destroyer near the Shetland Islands. The U-35 would crash dive and try to evade, but it would be found by the asdic onboard the HMS Icarus. 2 more British destroyers then joined the Icarus to launch their attacks and one of the depth charges damaged the diving planes on the U-35 and ruptured the aft fuel and ballast tanks. Knowing that the boat was doomed the captain of the U-35 ordered all the tanks to be blown to bring the U-boat to the surface which allowed all 43 men to get off the boat, and to be rescued by their British pursuers. The loss of a U-boat at this stage of the war was always a problem for the Germans, but when it came to the goal of intercepting British shipping, the larger problem is that the attempted actions against the Royal Navy diverted many of the meagre resources that were available for work in the North Atlantic. A combination of the small number of boats available for operations, and the continued challenges with getting torpedoes to actually explode meant that numbers for November were bleak. One interesting development was that during an attack on the British freighter Rothesay Castle the U-49 would be attacked by two British destroyers. During this attack the U-49 would descend to a depth of 557 feet, which was far greater than what was believed to be possible, with the assumption being that the Type VIIB would have been crushed at a much higher depth. This was valuable information that would be used by other U-boat captains to help evade British destroyer attacks in the future, especially due to the fact that in the early stages of the war the maximum depth setting of British depth charges was only 500 feet. For a variety of reasons there would be only two U-boats available for operations in early December. Prien in his U-47 would have his third war patrol, enough to earn the entire crew the U-boat badge which U-boat crew members earned after three patrols. On this early December cruise the U-47 would find and sink three merchant ships in a span of just 5 days, two freighters and a tanker which combined totaled just a bit over 23,000 tons which brought the U-47s wartime total up to 61,500 tons. The other U-boat to launch a December patrol was the U-48 which would be active for just 7 days, but those 7 days would be even more lucrative with a total of 4 ships and over 25,000 tons successfully sank. While these two cruises were very efficient in terms of the number of days on station and the number of merchant ships attacked, they could not make up for the fact that there were just 16 total Atlantic patrols by U-boats in the last 3 months of 1939. These 16 patrols also only sank ships at roughly the same rate as the September patrols, they were not more efficient and so the lower number of patrols simply meant less total tonnage attacked. To make matters worse of the 16, 3 of the U-boats did not return, and the U-35 was lost in the North Sea operations. It was clear that U-boats were good at attacking merchant shipping and sinking merchant ships, but in late 1939 it was not able to do so at the rate that would be required to begin to put a serious dent in the merchant tonnage available to Britain. The German leaders could only hope that 1940 would be a better year.

During the first two months of 1940 a major problem was weather. There was no avoiding the fact that during the winter months all naval operations would be more difficult, and that included U-boat operations because U-boats spent most of their time on the surface. The very cold winter would also cause ice problems on the German north sea coast which would just slow everything down. Even with some of these challenges 18 total patrols of the Atlantic would be launched which would result in the sinking of a total of 58 ships through a combination of torpedoes and mines. However, of the 18 U-boats used, 5 of them would not return. Then after February the entire Atlantic U-boat campaign would be put on pause so that all of the tools of the Kriegsmarine could be focused on supporting the campaign against Norway which was scheduled to begin in March. So this marks a good moment to look at the effectiveness of U-boat operations during the first 6 months of the war. For the Germans the good news was that they had been able to sink 277 ships, with a little under half of those being British flagged vessels. In total these ships were just under a million total tons, 974,000. During this same time total imports into the British isles dropped by about a 1/4, but this was not completely attributed to just the successful U-boat attacks. The act of convoying introduced a large amount of inefficiency into the trade networks, with time taken on both ends of a convoy to group ships together and then to disperse to ports for unloading. This just made things slower than when all of the ships simply sailed individually. But I think it is reasonable to attribute some of this to U-boats, they were forcing the British to be less efficient with their trade networks, which was a victory all of its own. The downside of this was that over the course of this same period of time 17 total U-boats were lost, about a 1/3 of the entire U-boat force at the start of the war, including the smaller U-boats only used in the North Sea.