160: Opening U-Boat Moves


When the war started the German U-boats were already prepared to play their part.



Hello everyone and welcome to History of the Second World War Episode 160 - The Early War at Sea - Opening U-Boat Moves. This week a big thank you goes out to James for becoming a member, you can find out more at historyofthesecondworldwar.com/members. When war was declared between Germany and Great Britain on September 3, 1939 the Battle of the Atlantic started as the German U-boats began their attacks on enemy merchant shipping. The early months of the Battle of the Atlantic would be unique in many ways. First of all, the U-boats were acting under very stringent rules of engagement that were not what Raeder, Donitz, and the rest of the Kriegsmarine believed they needed for victory. These rules would not be changed until later in the month, which resulted in the interesting statistic that during September 1939 about a 1/4 of all ships that were sank by U-boats were actually put under the waves by the U-boat’s deck guns instead of torpedoes. During this time the U-boats were also under orders to attempt to rescue the crew, a risky procedure that forced the U-boat to remain on the surface and in the area of the attack for far longer than they wanted. Even with these handicaps the U-boat fleet would very quickly have an impact on the war, an impact that this episode will discuss, before then also discussing the curious case of the British Anti-Submarine Strike Forces, which would be a debacle of the highest order.

One of the challenges faced by the Kriegsmarine’s U-boat fleet was that there simply was never enough of them. This is at least partially due to the fact that Germany was not allowed to build U-boats until after the Anglo-German Naval treaty was signed in 1935 which allowed them to build 24,000 tons of U-boats. With this allowance, 12,500 tons would be used to order and assemble 36 U-boats that had already been planned and partially built. This allowed for a quick burst of construction which allowed most of these U-boats to all enter the fleet by 1936. But after this initial burst things would greatly slow down and there would also be major differences in how Donitz and Raeder believed the remaining 11,500 tons should be spent. Donitz was heavily focused on what he believed was the best available submarine design for interdicting British trade in the North Atlantic and Western Approaches the Type VII medium submarine. The Type VII, and its later variants, would go on to be the most numerous German submarine of the war years, but in the mid 1930s there was some debate about whether or not it was the best possible option. Others within the German Nay preferred to built several different types of U-boat, with smaller versions that were better suited for action in the North Sea and larger submarines which were capable of longer range operations at the cost of performance. These larger Type IXs did not have the dive speed or maneuverability of the Type VIIs and Donitz believed that this would make them very vulnerable in a combat environment. They would also take much longer to build, which would slow the overall growth rate of the German U-boat forces. The support for the Type IXs primarily came from their greater radius of action, and their ability to stay on station longer, which was an important factor in German U-boat operations, because the Type VIIs would spend a lot of time going from ports in Germany to the Atlantic, have a limited window when they could stay at sea before making their way back. This problem would be reduced by the capture of French ports in 1940, but that is not something that could be planned for or counted on in the mid-1930s. The disagreements around the type, some construction challenges, and then the emphasis placed on the Type IX’s, resulted in only 1 German U-boat being commissioned in 1937. Then in 1938 only 9 would be commissioned, and in the first 8 months of 1939 only 12. Much like other arms of the Kriegsmarine, there were major plans for expansion of the U-boat forces under Plan Z, but also like the other areas of the Kriegsmarine no real work had started on those Plan Z submarines before the start of the war. The official movement of the German U-boat forces from a peace time footing to a war footing would begin on August 15th, about 2 weeks before the war would begin. On that date an order would be sent out for all senior staff officers and U-boat commanders to report to Donitz’s headquarters on the 19th. During this meeting the first war orders would be given for the 20 oceangoing U-boats that would be prepared for war in late August, the primarily focus of this episode will be on these ocean going U-boats, with there also being smaller coastal U-boats that would spend their time in the North Sea and on minelaying operations. The available oceangoing U-boats would be split into a few different flotillas, with each given a patrol area. The Salzwedel Flotilla would be comprised of 6 type VIIs which would patrol just to the West of the British Isles. The Wegener Flotilla, with six Type VIIB’s, with the primary improvement being a much higher fuel capacity, assigned a similar patrol zone, but shifted further west out into the Atlantic. Finally, the Hundius flotilla would have 5 of the long range type IXs and they would patrol further south around the Iberian peninsula and the approaches to the Strait of Gibraltar. Importantly, all of these submarines would be acting under the 1930 Submarine protocol, an international agreement that Germany was a signatory of which contained the agreement that ships would not be sunk without warning. As mentioned earlier, this was a decision made with an understanding that it would drastically reduce the effectiveness of the U-boats, with the hope being that such restraint would make it more likely that a peace could be brokered with France and Britain after the invasion of Poland was complete.

On September third just before 1PM Berlin time, a message was sent to all vessels and shore installations of the Kriegsmarine “Hostilities with England effective immediately.” You might notice something a bit weird about that message “Hostilities with England effective immediately.” that is correct, in the hopes that France might be convinced to exit the war the U-boats were not allowed to attack any French ships to further clarify this specific part of the earlier order a few hours later the message was sent “Boats are to take no hostile action against [French] merchant ships for the present, except in self-defense.” This order further restricted the targets available to the U-boats and their ability to have an impact on the war. Almost more importantly it greatly impacted their ability to attack at night, which was one of their most potent tactics. This is because even though the U-boats could operate underwater, they were generally better able to attack merchant ships if they were on the surface, and the only time that was possible was at night. But it was essentially impossible to identify the merchant ships and their countries of origin at night. Eve with all of these restrictions it would take just a few hours before the first U-boat attack of the war would be launched by the U-30 commanded by Fritz-Julius Lemp. Lemp believed that when he spotted a British ship it was armed with deck guns, which would make it an auxiliary cruiser and a warship, which meant he could attack it without warning. And so at around 7:40PM two torpedoes were launched and hit the ship. The problem was that the merchant ship was not an auxiliary cruiser but instead the S.S. Athenia which was carrying over 1,100 passengers, including over 300 Americans. I’m calling out the Americans here specifically because it was incidents like these that played a major role in America entering into the First World War, and in the new war that had just started the same type of events were occurring just hours after hostilities had started. Fortunately for everyone aboard the Athenia the ship would not sink quickly, and in fact it would remain afloat all through the night which allowed the vast majority of the passengers and crew to be rescued by other merchant ships and 3 British destroyers which were dispatched to the scene, with the final death toll being 118. Reports of this attack would circle the globe very quickly, with the German government issuing an official denial of the attack, claiming that the Athenia much had hit a mine. However, an order would be sent out on September 4th which stated that “By order of the Führer: No hostile action is to be taken for the present against passenger ships, even in convoy.” Even under these restrictive rules, some of the U-boats would still be successful in their missions during these early days of the war, and one of the most successful was the Type VIIB U-47 under the command of Günther Prien. Prien would go on to be one of the most famous U-boat commanders of the war, although his relatively short period of time in active service before his death in early 1941 limited his total tonnage numbers. On September 5th he would make his first attack of the war, when the U-47 spotted the Bosnia, a 2,400 ton British freighter about 300 miles west off the French coast. Obeying orders, the U-47 surfaced and fired a round from its deck gun at the freighter, which immediately increased speed and began transmitting the U-boat attack radio message of SSS. Prien would order 4 more rounds from the gun fired at the ship, with 3 of them hitting, at which point the crew abandoned ship. The U-47 would go amongst the crew which was in the water and bring them aboard the U-47, getting one of the freighter’s lifeboats ready for them before a Norwegian merchant ship arrived and the Bosnia’s crew was loaded onto the German ship. After everyone was safely out of the way a single torpedo was used to sink the Bosnia. It would not take long for Prien to find its next victim, when the Rio Claro a d 4,000 ton British freighter was spotted on September 6th. Again after firing one shell the SSS signal started so 3 more deck gun shots were fired at the bridge of the ship, which caused the radio signals to end and the crew to abandon ship. After the crew were in lifeboats another torpedo was dispatched to sink the Rio Claro. The next day another ship was spotted, the much smaller Gartavon, which was sank with fire from the deck gun after the first torpedo that was fired from the U-47 malfunctioned, which would become a theme for the German U-boat commanders in the early weeks and months of the war.

Another area of action during the early weeks of the war was the North Sea, while the U-boat actions in the Atlantic would always be the most glamorous areas of U-boat operations but there was also important work being done in the North Sea. When the war started there were 17 small submarines in the North sea that would begin both offensive and defensive operations against enemy shipping. Some of these U-boats were committed to minelaying operations along the British coast with a few of these minefields being very successful and sinking multiple British merchant ships in the weeks that followed. Other U-boats would be able to execute attacks against shipping in the North Sea, but they were frequently thwarted by the failures of the German torpedoes. For example U-23, commanded by Otto Kretschmer who would later became the most successful U-boat commander of the entire war, would fire 4 torpedoes at a single ship, all of which would fail to explode. Other submarines were far more successful, with a total of 2 ships sank by U-boats in the North sea before September 22nd when the rules of engagement would be changed for the North Sea, allowing the U-boats to more proactively attack neutral shipping. The new rules of engagement would allow for 10 neutral merchant ships to be sank or captured in just 1 week. However, these successes resulted in protests from other neutral nations, especially those bordering the North Sea, Denmark, Norway, Sweden, and Finland. This resulted in another change of orders to bring back many of the previous restrictions on September 30th to try and reduce the anger from the neutral nations. Overall the first month of operations in the North Sea were disappointing, and the overall numbers only approached reasonable when the minefields were included. The one benefit of these early operations would be that some of the most successful U-boat commanders of the war would get their first combat experience during these early operations in very small U-boats in the North Sea.

Even though there were some successes in the early days and weeks of the war, Dönitz and the staff officers commanding Germany’s U-boat forces had to start thinking about the future. This would result in orders being sent out on September 8th which would order 10 of the 18 U-boats that were currently in the Atlantic to begin making their way back to Germany. On their way back they would still be continuing operations, as they would be traveling through target rich areas, but they needed to come back to Germany to prepare for the future. This was because, when the initial war time deployments began, essentially every operational U-boat in the Kriegsmarine was committed to those operations, and this left no reserves in Germany to replace them. So if every U-boat remained for their maximum cruise duration in September there would be essentially no U-boats on patrol for a good portion of October. The only way to fix this was to pre-emptively draw down the strength on patrol in September so that the u-boats could return to port to rearm, resupply, and prepare for operations in October. This was not a great solution, but it was the only one available to solve for the fact that there simply were not enough U-boats available to achieve the goals of the U-boat campaign, and there were very few that would be added to the fleet in the short term. Due to the length of time it took to build a U-boat, it was well known how many new U-boats would enter the fleet in late 1939 and early 1940, and the numbers were grim, by March 1940 just 6 new medium or large U-boats would enter the fleet, 6. And in September 2 oceangoing U-boats were lost, a worrying trend which meant that already loss rates were above replacement rates. To make matters worse, at least in Dönitz’s mind, was the constant pull to use the oceangoing U-boats for missions other than those strictly focused on attacks on shipping, with constant calls for U-boats to perform minelaying operations as far away as Gibraltar which could only be reached by the larger oceangoing U-boats. The mining plans as written would have required the entire U-boat fleet to participate, essentially removing them from the trade routes for a sizeable portion of time. This would be a constant battle for Dönitz during the early years of the war, before he would replace Raeder and gain full control of the Kriegsmarine. The root cause of this problem was simply numbers though, and that problem could only be solved over a long period of time. There would be a massive shift in resources from other naval construction efforts to submarines in the early months of the war, since they were faster and easier to build than the large capital ships of Plan Z, but it would not be until late in 1940 that any of these new U-boats would near completion and it would be even longer before the fleet would grow in size at a reasonable rate. Another major problem was the fact that even when U-boats were on station, and were able to locate shipping to attack, the torpedoes that they were firing were frequently failing. But this problem would take time to solve not just because it had to be identified as a problem, but it would also take time before the engineers and staff officers in charge of torpedo design and construction were even convinced that there was a problem. They would instead blame the U-boat captains for simply missing with their torpedo attacks, instead of believing the captains that the torpedoes were either hitting the target ships or getting close enough that the magnetic detonators should have caused them to explode. This would result in a very frustrating time for the U-boat captains, and it would be months before a resolution would be found.

The British had their own problems, one of which was based around one of their theories on how to combat the German U-boat threat: Antisubmarine strike forces. This was an idea that was heavily supported by Churchill and was based around the theory that carrier based aircraft and destroyers, working together, would be able to find and sink any submarine within range. If the U-boat tried to work on the surface the carrier based aircraft could spot it and attack it, or at the very least force it to submerge where it would be slower. If the U-boat did submerge then the destroyers could move in and find and attack it with asdic and depth charges. In theory you could say that this was a reasonable idea, but there were two major problems that would not be solved before the war, or even during the war once these hunter-killer groups were put into play. The first was that by using a carrier for anti-submarine work, you had to obviously put the carrier in an area with submarines, which was very dangerous. Carriers were big targets, and they were probably only second to battleships on the priority list for U-boat captains, if they found a carrier they were probably going to do their best to sink it. The second major problem it that while this concept had its supporters, it had never really been tried even in peacetime, this meant that the carriers and their aircraft had very little experience hunting for submarines. Spotting U-boats from the air was at times very difficult, and even when they were spotted there was no way for the aircraft to maintain any form of contact if they submerged. In theory this would be the moment when the destroyers would come into play, but it took time for destroyers to arrive on the scene, giving the U-boat captains plenty of time to maneuver away. It didn’t help that there were generally only a handful of destroyers with a carrier, so if some of them were off in one area trying to find and sink a U-boat, there was very little to stop another U-boat from launching an attack on the carrier. Finally, even if the hunter-killer groups did sink some U-boats, the risk and reward was so heavily skewed towards risk that they needed to sink most of the U-boats in existence in late 1939 for it to be worth it. The British were willfully risking an aircraft carrier, which they only had a handful at the start of the war, and which they would complete under 10 of during the war to combat U-boats which the Germans would 1,100 of during the war, to make that worth it the hunter-killer groups would have to sink 100 submarines for every carrier lost, and that would be how it would go.

On September 14th the weaknesses but also the power of the carrier based anti-submarine strike forces would be on full display around the carrier Ark Royal. The actions that day started well, with the strike force discovering the U-30 submarine and moving in for an attack. The Ark Royal turned into the wind to launch a flight of Skuas to assist the destroyers, and in doing so became separated from the 3 destroyers that had stayed behind to screen the carrier. What none of the four ships knew was that the U-39, a Type XI which was on its way back to base due to Dönitz’s recall order had spotted the Ark Royal and was moving into attack. At 3:07PM the submarine launched 3 magnetic torpedos, but they were either misaimed or malfunctioned because none of them hit the Ark Royal. But they were spotted by the Ark Royal and so the three destroyers moved in to attack the U-39. Within minutes two of the destroyers had asdic contact with the submarine and one of them moved in to attack while the other then did the same. In the meantime the third destroyer was able to arrive and maintain the asdic contact after the depth charges of the other destroyers had exploded, and then moved in to launch its own attack. In total 12 depth charges would explode near the U-boat, and the captain of U-39 Gerhard Glattes decided that the only option was to abandon ship, and so the tanks were blown so that the U-boat would surface and all of the crew could evacuate before scuttling charges exploded to send the U-boat below the waves. 43 of the crew were brought on board the British destroyers. Overall this was a successful example of the theory of the strike forces, but it was only possible because of the malfunction of the German torpedoes, if they had actually worked as designed then it was very possible that the carrier would have joined the U-boat at the bottom of the ocean, which would have been a very poor trade.

Speaking of poor trades, that brings us to the HMS Courageous which was another British aircraft carrier which would also encounter two U-boats just three days after the Ark Royal on September 17th. The situation for the Courageous was not that much different than what had happened to Ark Royal. Two U-boats, the U-53 and U-29, had been sent towards the expected position of the British convoy which just to happened to be the same path as the Courageous. On September 17th the Courageous would launch a flight of Swordfish to attack the U-53 after it had been spotted, with the Swordfish launching their ineffective attack on the U-53. On the same afternoon the U-29 spotted the Courageous and tried to move into attack but the British carrier was simply too fast for the U-boat to catch, until it had to turn into the wind to allow for landing operations to begin. This brought the carrier right into the perfect path for the U-29 to launch an attack, with three torpedoes launched at a range of around 2,700 meters, with the range rapidly closing. Two of the torpedoes would hit, after running for just over 2 minutes. Two of the escorting destroyers moved into attack the U-29 and would eventually use all of their depth charges without successfully sinking the U-boat. On the Courageous there was no warning of the torpedoes until they exploded under the ship at 7:55PM. The two hits severed the electrical main which cut all power aboard the ship and disabled the radios. As water poured into the ship through the holes created by the torpedoes, a decision taken that day for some of the important water tight doors, called X doors, to remain open allowed water to freely moved throughout the ship. The X doors were supposed to remain such at all times but orders had been given for some of them to be open for ventilation purposes, it may not have been the cause of the sinking, but is certainly did not help. The carrier immediately took on a list that would quickly increase, and it was clear that the ship was going to go down. The problem was that the heavy list made the starboard side lifeboats unable to be launched, while on the port side several of the boats had been destroyed or were inoperable. This meant that most of the crew had to swim for it. The carrier would sink just 15 minutes after the torpedoes struck, given only limited time for men to abandon ship. The accompanying destroyers would to the best that they could, with the Impulsive pulling over 350 men out of the water and the dido over 200, while they were also joined by several nearby merchant steamers. In total of the 1,260 crew of the Courageous just 741 men were rescued, with 519 being killed. Immediately after the news of the Courageous reached the Admiralty the other carriers that were performing antisubmarine duties were withdrawn while the entire concept was re-evaluated. The U-29 and its captain Otto Schuhart would be able to claim the sinking of the Courageous along with two British tankers, which would be a single patrol tonnage record that would stand for some time, at 41,905 tons. For the Royal Navy, the sinking of the Courageous would be a major blow, and not the only U-boat attack on a Royal Navy capital ship in the opening months of the war, because next episode will discuss the actions of the U-47 which would make its way into Scapa Flow in mid October, 1939.