154: Opening Moves


When the war started in Poland, so did the war at sea.



Hello everyone and welcome to History of the Second World War Episode 154 - The Early War at Sea Pt. 4 - Opening Moves. This week a big thank you goes out to B, Eric, Goran, David, Cam, and Ryan for choosing to support the podcast by becoming members, find out more at historyofthesecondworldwar.com/members. The early months of the Second World War in Europe were an interesting time for the war at sea. This was not due to major naval actions like what the Japanese would launch at the start of the war in the Pacific but instead due to scattered actions of the Kriegsmarine and the somewhat frantic actions of the Royal Navy to answer them. From basically the very beginning of the war two trends would be apparent, and they would be themes that would continue really until 1941. The first theme is that the Kriegsmarine never had enough vessels, either surface or underwater, to accomplish their goals. Many of these goals were around commerce raiding on the surface and then attacks on the British fleet from submarines, both of which would be successful on a limited scale. But simply due to a lack of resources those actions could not change the course of the war or decisively influence British trade. On the opposite side the theme for the Royal Navy was unrelenting frustration that was only broken by periodic victories. We will discuss this frustration in great detail starting in Episode 6 of this series which will cover the actions of the two Panzerschiffe that would be in position to do some commerce raiding when the war started, and then we will cover another area of great frustration starting in Episode 9 which will cover the actions of German U-boats, but this frustration would also manifest in more subtle ways. For example attacks on Scapa Flow, the traditional fleet anchorage, from both the air and by U-Boats would force the fleet to move to western Scotland, making it more difficult to project power into the North Sea and the actions of German surface raiders would force the Royal Navy to spread its forces out to try and guard the convoys that were plying the northern Atlantic and Western Approaches, making it difficult to concentrate forces against any single German threat. It was a disappointing beginning for a Navy that prided itself on its tremendous strength and its general competency. This episode will focus on the very beginning of the war and some of the first actions taken by both sides in the conflict, particularly around the merchant fleets of both nations.

A critical piece of planning for both Britain and Germany before the war had nothing to do with battleships, aircraft, or submarines but instead all revolved around merchant shipping. This is because when the German U-Boat campaign was being planned it had nothing to do with the contents of the ships that were being sunk. Yes, it was great that the contents of those ships were not reaching Britain or whatever their destination might be, but the more important thing was that the ship was at the bottom of the ocean instead of being able to carry further cargo. This is a fact that is easy to miss because most statistics about the U-boat campaign focus on the tonnage of material that was sunk, but the more important number for the long term success of the German efforts was the reduction in the total carrying capacity of the merchant ships available to the British merchant marine. This is also one of the reasons that the entry of the United States into the war was such a critical moment for the Battle of the Atlantic, and then the mass creation of Liberty ships which were just relatively simple, but very easy to mass produce merchant ships, it meant that no matter how many ships the U-boats successfully sank, they could never make headway against the total shipping tonnage of the Allied merchant fleets. At the start of the war the British merchant fleet had a carrying capacity of 21 million tons, which was a lot, but it was not enough. This fact became clear shortly after the start of the war when even that many merchant ships were not able to support the full needs placed on British imports due to the increased needs for the war effort. This problem only became worse due to both the number of ships that were sunk during the first months of the war, many of which were actually sunk by mines and not U-Boats, but was also exacerbated by the inefficiencies that were introduced into the trade system by convoying. The convoy system, by its very nature slowed down trade, something that greatly displeased ship owners, because it required the ships to get together, then sail based on the speed of the slowest ship, and then disperse on the other end. But unlike during the First World War, during which the Royal Navy resisted the introduction of convoys, the introduction of a system of convoying was a critical part of British war plans and at the very start of the war a system was setup whereby ships were grouped into different convoys based on destination and speed. The exact speed of the convoy was critical due to the importance of station keeping within the convoy, especially when the convoy included zig zag patterns. The movements of the convoy were generally complicated enough that there was a conference before any convoy departed where the masters, chief engineers, and wireless operators of all of the merchantmen would come together to be briefed on expected speed, wireless codes, and zigzag patterns. All of these items had to be discussed before hand, and then also there had to be a coordinated plan for what to happen in case of attack, otherwise the risk of ships colliding, or just general confusion was very high. This put a lot of strain on the masters of the ships that often was not present during peacetime operations. At the beginning of the war there were more exceptions to the convoy system though. The first was for ships that were able to maintain a speed of greater than 15 knots, with the assumption being that these ships were able to move fast enough to mostly outpace the U-boats that were hunting for them, and by blasting with speed through the danger zone they might actually be safer than going slower with a convoy. This would eventually be changed, especially as the number of faster ships grew and they could be grouped into simply faster convoys. Slower ships, or those that were incapable of matching a 9 knot convoy speed were also not included, due to fears that a slower speed would just make the convoy more vulnerable. The vulnerability of slower ships eventually meant that they would also be grouped into convoys, just convoys that maintained a slower speed that they were capable of. The final group of merchant ships that were initially excluded from convoys were neutral merchant ships, which were often either bound for British or neutral ports. They would also be added into the convoy system, especially as their importance to British shipping would grow after only a few weeks of the war. The first group of neutral shipping to join the British merchant fleet were those of the Polish merchant marine, after the invasion of Poland any Polish flagged vessels that were not captured by the Germans were integrated into the British shipping fleet. They would then later be joined by the ships of many other nations, particularly those of Denmark, Belgium, the Netherlands, and Norway. These ships were a critical area of expansion for the British merchant fleet, and greatly reduced the impact of the victories of the U-boats and the losses suffered due to German mines. Even before the nations were captured by German ground forces, many of the merchant fleets worked closely with the British government through the creation of bilateral shipping agreements. There was risk of joining British convoys, but this could be offset by insurance guaranteed by the British government, and there was no shortage of money floating around to pay for the ships. The British merchant marine would also prepare for the war by arming themselves. The process of getting at least some merchant ships armed began as early as the Munich Crisis when the British Ministry of Shipping started to work with ship owners to strengthen decks and weld on mountings that could later be used to mount 4 or 6 inch guns on the ships that would hopefully provide at least some protection from German surface ships and surfaced submarines. The guns would begin to be mounted in June 1939 as war seemed imminent, and the efforts were coordinated by the Admiralty Trade Division. This was made much easier due to the large number of 4 and 6 inch guns that were sitting in British warehouses after the ships that originally housed them were broken up during the 1920s due to the Washington Naval Treaty. The efficacy of these guns was questionable, but if nothing else it gave the merchant fleet at least the illusion of being able to defend themselves. There would also be attempts to use merchant ships in a more dedicated military role in the form of Armoured Merchant Cruisers or AMCs. AMCs were a topic that both Britain and Germany would spend a good amount of thought and resources on before the war under the theory that faster merchant ships might be a great supplement to the fleets of both nations as they tried to prevent the trade of the other, or protect their own trade. The results of these AMCs would be disappointing at best, and a complete failure at worst, with British AMCs proving to be very vulnerable to both German surface ships, particularly the Panzershiffe, and also incapable of protecting British convoys from German submarines. This would result in a de-emphasis of the AMC concept in December 1939, with a reallocation of any resources for more AMC conversions being placed into simply a greater emphasis on the construction of dedicated convoy escort vessels.

The importance of trade to Britain is a topic that I am sure very few listeners to this podcast are surprised by, it plays such a critical role in the telling of any history of Britain in the Second World War. A topic that gets less discussion is the fate and importance of the German merchant fleet. When the war started around 400 German merchant ships were abroad, and the Royal Navy would spend the first several months of the war making an effort to either sink them or at least prevent them from returning to Germany. This would be accomplished both by actively hunting them down in various areas around the world, but also simply by maintaining a blockade of the North Sea to prevent them from returning home. This would not prevent many of the ships from actually making it back to Germany though, and up to April 1940 82 German merchant ships were able to make it back to Germany. When they arrived back in Germany some of these ships were able to join in the important trade with Scandinavia, with Swedish Iron ore being shipped to Germany, but most of them would be unable to really contribute further to the war effort due to British efforts to interdict German trade. This would be accomplished by the Northern Patrol of cruisers and AMCs which would have their first success on the very first day of the war with the capture of the 2,377 ton Hannah Boge south of Iceland. So why have I spent half of an episode just talking about the make up and plans of the merchant fleets of the nations of Europe? Mostly because the naval actions of both Britain and Germany would be entirely structured by trade war for the entire war. When looking at land campaigns it is often critical to talk about geography, rivers, mountains, forests, and similar geographic features have critical impacts on the actions of armies. Well, for the European naval war everything would be focused on the attack and defense of British trade and it would entirely dictate almost every action of the German war either directly or indirectly for the entirety of the war. And because it dictated the actions of the Kriegsmarine it also dictated the actions of the Royal Navy in response.


Even before the war officially started between Britain and Germany in September 1939 both sides were preparing for war. In Britain the Royal Naval Reserve and the Royal Naval Volunteer Reserve were at least partially activated starting in June 1939 to man the ships of the Reserve Fleet that were pulled back into service at that time. Then in late August, very close to the start of the war a general mobilization of those groups was put into place to put the Royal Navy on a war footing. The activation of these reserves would increase the manpower of the Royal Navy from around 130,000 to over 210,000. This would be just in time because on September 3rd signals would be issued from London to all British naval units around the world that the nation was at war. The first would be issued just after 11AM with the simple content of “Most immediate: Total Germany” which was the prearranged message that Britain was not at war with Germany and that actions to that effect should be taken immediately. Commander Alastair Ewing would be on board the destroyer Imogen in the Mediterranean when this message arrived, and he would record his thoughts at that time like this: “At 11 a.m. our ultimatum to Germany expired and we were at war. This called for champagne, not to celebrate but to mark the occasion. I was rather glad it had come. There could be no other honourable course of action and during the whole of these last few days, I have had the uncomfortable feeling that our politicians were striving desperately to find an easy way out, like Munich. But it is certainly fighting for an ideal and it will not be easy to bring any immediate aid to Poland. Italy is apparently not coming in, which simplifies our job at sea 100%”. At the same time coordination plans with the French were activated, with all French ports closed starting on September 1st when news arrived of the invasion of Poland. These restrictions were reduced as soon as it was obvious that a German invasion of France was not going to happen immediately, and also that Italy was not going to join the war. This allowed the western Atlantic French ports to open on the 5th along with ports in the Mediterranean. In all cases French ships were subordinated completely to the British convoy system, with the French government essentially handing all of their merchant ships to the British to coordinate and protect as they were moving French trade across the Atlantic. At the same time the Kriegsmarine was preparing to use its resources to meet its own objectives. One of the first actions taken to meet these objectives was the laying of minefields in the Baltic which would be done on September 4th with three minelayers laying minefields totally 564 mines, effectively closing part of the entrances to the Baltic sea. Along with this there would be a concerted effort to interdict all trade in the Baltic that might be bound for Britain for France. These efforts would largely be successful, but mostly only because most shipping bound for Britain and France, including many Polish merchant ships had already vacated the Baltic due to the threat of war. This meant that many of the vessels that were stopped and searched by German destroyers were allowed to continue their trade due to their contents and their destinations.

The efforts of German U-Boats to interdict British trade will be a major topic for later in this series, but it is impossible to discuss any aspect of the preparations for the war, and then the first months of the conflict, without at least touching on the plans of the U-Boats and the plans of the Royal Navy to protect against them. Within the Kriegsmarine, Admiral Karl Dönitz was the lead advocate and the commander of the German U-Boat fleet. Dönitz’s firm belief that the U-Boats were the path to victory would come into conflict’s with Raeder’s vision of the best path forward for the Kriegsmarine, which he believed needed at least some focus on mining the sea lanes and controlling them with surface vessels. Raeder’s control of the German navy meant that resources that could have gone to U-Boat construction before the war were used for other purposes, and this meant that the number of U-boats available for surface, and particularly u-boats with the endurance to operate in the Atlantic were limited. This often meant that there were only a handful of U-boats on patrol early in the war, and even then those numbers were only possible by pulsing operations, with a month of heavy patrolling followed by a month of relatively few patrols as u-boats returned to port, rearmed and refitted before the next pulse. Even these small numbers would have some effect, sinking around 200,000 tons of shipping in the first few months of the war, and they were greatly aided by German signals intelligence. The most popular story of signals intelligence during the early years of the war would be the efforts of the British code breakers to read the German Enigma encrypted messages. But on the German side, major efforts were undertaken to decipher and use Allied messages for the aid of all aspects of the war, including the U-boats.

This would pay off in major ways during the early part of the war because xB-Dienst, the decryption arm of the German radio monitoring service was able to read almost all Allied radio communications, including those used by the Royal Navy .The ability to read these communications gave the German navy almost perfect knowledge of the position of British warships and convoys, which allowed them to position their own sparse resources in ways that they were far more useful than they might have otherwise have been. Another major boon for the Germans in the early years of the war was the usage of mines, there were major efforts by the German Navy to sow minefields in areas around the north sea and around Britain through surface vessels, U-boats, and by air. The key was that the Germans had developed a potent magnetic mine before the war, which was more consistent and deadly than contact mines because it could detonate when a ship was passing over it due to the disturbance that the metal hulled ships had on the magnetic field around the mine. These efforts, both in the development of the mines and in the efforts to place them would be vindicated early and often during the war, with more shipping tonnage sank via mines than by U-boats during 1939. The presence of mines and the threat of U-boats would force British efforts and resources to be allocated to countering the threats. In the case of mines this meant the creation of more and more minesweepers, with almost 600 ships requisitioned for minesweeping duties by the end of the year, to add onto the number that were constructed during that time and had existed before the war.

These were generally very small coastal vessels, trawlers, yachts, and similar ships that were fitted with minesweeping equipment. Similar efforts were made to bolster the size of British anti-submarine forces. There was also a tremendous amount of trust and faith placed in asdic, an early form of sonar that was developed during the First World War and then refined during the interwar years. Asdic used narrow soundwaves to detect submarines, which would be discovered when the soundwaves bounced off of them and were returned to the vessel where it was detected by hydrophones. And this tool did work, and there would be 180 different vessels of various sizes with asdic sets fitted at the start of the war. But there were many limitations that would reduce the effectiveness of asdic below what was expected before the war. The first was simply that asdic as a system had limited range, with the maximum possible detection range being only around 2,500 meters and that range could be heavily impacted based on weather conditions and the exact placement and positioning o the submarine. Another challenge is that even with 180 asdic sets, these were often spread very thin, and this made it challenging to get groups of asdic ships together to attack submarines in groups. This was critical because the efficacy of asdic was greatly impacted by depth charges, which meant that it was often very difficult for a ship that had asdic to fine the submarine, drop depth charges, and then reacquire the submarine again, which often allowed them to escape. Another challenge was simply that the U-boats really liked to attack convoys at night and on the surface, which removed the ability of asdic to detect them. Finally, there simply was not enough trained and experienced asdic operators at the start of the war, and that problem only got worse as the number of convoy escort vessels expanded greatly in the first months and year of the war. It would take time for this experience to be gained, and there was really no way around it. Luckily for the Royal Navy, and the British trade, the Germans did not have as many U-boats as they would have liked, and so while the U-boats would begin sinking ships almost immediately after the start of the war there would be time to build up the ability to protect from U-boat attack before the critical phases of the Battle of the Atlantic would begin in 1940.