209: Electronic Tripwires

Description

In the years before the war the new technology of radar would begin to solve many of the problems of air defense, but it was not perfect.

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Transcript

Hello everyone and welcome to History of the Second World War Episode 209 - The Battle Before Britain Pt. 1 - Electronic Tripwires. If you have not yet, you should to back and listen to the Season Introduction episode that released yesterday, it talks about the upcoming episodes and how the Battle of Britain episodes will be broken down into several mini-series. It also has good information about what you can expect from the next year or so of the podcast. Also, since this marks the beginning of a new season, and I just took a bit of a break, the new member list is lengthy: thank you to: Schuyler, Kieran, Melissa, Ben, Jack, David, Ayaan, Dallas, Tyler, scienceandhonor, Max, David, David, Ben, and Jason for choosing to support the podcast by becoming members and to Kevin, Philip, Luis, and Bono for the donation. You can find out how to support the podcast over at historyofthesecondworldwar.com/members. Even before the armistice came into effect on June 22 and France exited from its active participation in the war the British were faced with a question, what were they supposed to do moving forward. They had entered the war as part of a coalition against Germany, with France and Britain jointly entering the conflict due to the German violation of Polish territory in September 1939. Over the following 9 months there was nothing but disasters for Allies, Poland was occupied, then Denmark and Norway, then the German forces cascaded into Western Europe occupied The Netherlands, Belgium, and then Northern France. There were small victories within that time, or mitigations of defeat might be a better term, with events like the evacuation of Dunkirk saving many of the men from the British Expeditionary Force from being captured by the Germans, but it seemed like nothing could stop the German ground forces. That was, until they reached a bit of water known as the English Channel. The Germans were faced with a new challenge, how to stage an amphibious campaign unlike anything that they had attempted to do before, the next in a long line of continental generals that stared across the channel at the cliffs of dover and had to devise a way to get men and material across, and then keep them supplied during an invasion. To put it bluntly, their military was not equipped or designed for that type of operation, the largest bodies of water they were designed to cross were the rivers of Europe, and while earlier in the year they had staged the invasion of Norway that had been on a much smaller scale, and had itself cost the German Navy dearly. The Germans had known almost nothing but political and military victory since the Munich Agreement in 1938, but now they were faced with a challenge they had not prepared for. One objective that they believed they could accomplish was the suppression and dismantling of the British Royal Air Force, a prerequisite for any invasion effort, and something that Hermann Goering believed his Luftwaffe could easily accomplish. And why not? They had practically destroyed every air force they had encountered during the war, and in many cases it had not even really been a contest. The German Heer and Kriegsmarine went to work on crafting a plan to take advantage of the expected air superiority to bring across the channel, code named operation Sealion it would involved the use of almost every thing that the Germans could get their hands on that could float. There were disagreements, as there always were between Army and Navy leaders about amphibious operations, but they would surely be able to sort them out in time, and in the meantime the Luftwaffe could get to work. In Britain, well things had not gone well during the war, but in some ways the situation that the British found themselves in during the summer of 1940 was one that in some ways should have made them feel more comfortable. Defending their home islands were what the British military was designed to do, for centuries the Royal Navy had been built and maintained to protect against precisely what the Germans were wanting to do. They were the senior service, they were the long time protectors of the empire, and the Royal Navy fully intended to play its part should it be required, with operations planned to throw whatever was required against the German invasion fleet. They were joined by the Royal Air Force, a far younger arm of the British military having only been formed in 1918, but one that had been heavily invested in during the 1930s specifically to wage the kind of air war it now found itself in. The leaders of the Royal Air Force had always shown disdain for close air support operations of the Army, and now they did not have to worry about that, and instead they could focus all of their efforts on offensive bombing operations against the invasion preparations and defending against German bombing attacks by the men and machines of Fighter Command. What would rapidly become clear is that the Royal Air Force was actually more prepared for the battle that was about to take place than the Luftwaffe who were initiating that campaign. And perhaps most importantly, time was on the side of the British, with the window for invasion closing in the later months of the year, which would put a pause on preparations until 1941. The objectives and goals of the RAF were also more clear, all they had to do to win the battle of survive, to continue to exist, to continue to pose a threat, that is all. But of course the Battle of Britain, just like so much of the history of the Second World War, is about far more than the relatively small number of pilots that engaged in aerial combat over Britain, the Channel and the North Sea, and over Northern France during the last six months of 1940. The air campaigns of the Second World War brought war home to many on the homefront in ways that just a few generations before would have been unthinkable. Bombs would be dropped not just on military targets, not just on economic targets, but simply on the homes of average citizens. The goal was not just to inflict physical damage on bodies and buildings, but to inflict psychological damage on the minds of the people and on the souls of a nation. Whether it was the daylight bombing during the heights of the invasion scare or the night time Blitz that followed the Luftwaffe would attempt to break the spirit of Britain, and it would fail. Because if there was one indisputable rule of strategic bombing that was established during the Second World War it was that destroying the will of a nation to resist was drastically more difficult than anybody expected, and even the great Allied bombing campaigns of the later war years, which were orders of magnitude larger than what the Luftwaffe could accomplish in 1940, would have problems achieving that goal. Also much like the rest of the Second World War, the Battle of Britain was a technological battle, the people involved mattered, of course the pilots in their aircraft, but also the masses of individuals involved in supporting those machines, both on the airfields and in the factories, and all of the people manning defenses all over Britain, and their families, and their supporters, all of those people mattered, but the technology they used would either give them the advantage or give it to the enemy. And that is where this episode will begin, with one of those pieces of technology and one that I think you could convincingly say played a decisive role in the battle that followed: radar.

Radar was not a completely new technology in 1940, and had been under pretty constant development in several nations around the world during the 1930s. After being accidentally discovered in 1930 it would spread and many military leaders saw it for what it could be, and that was a solution to the greatest problem in airpower. With the rise of airpower during the First World War one of the major challenges was meeting the enemy in the right numbers, at the right time, there was a serious advantage for the offensive air force because they could concentrate their aircraft in an area, appear over the battlefield with very little notice, execute their attack, and escape before friendly aircraft could respond. The only real counter this was through the concept of standing air patrols, where pursuit, later called fighter, aircraft just wandered around in the air in the hope of running into the enemy, a practice that was difficult to sustain in the numbers required, and difficult on pilots due to the required flying hours. Radar, with its ability to at least give some idea of when enemy aircraft were approaching, was a possible solution to this. There were many technical problems to overcome, the first of which was that the range of early radar sets were quite small, due to a limit to how much power could be pushed through the radar system and how much could be easily generated for the purpose. However all of this would improve with time. It should also be noted that radar was not the only solution to this problem that was conceived during this time, and there were other options that were investigated in at least some way during the interwar years. This included technologies like one named “Silhouette” which would involve massive numbers of searchlights which would illuminate clouds at night to spotlight any bombers. Once there was enough light fighters could wait above enemy bombers and pounce on them. There were also ideas for aerial minefields, perhaps held in place by balloons which would prevent enemy aircraft from flying over. Some time was also put into an idea where rockets would be fired into the sky when an enemy raid approached, with the idea that the rockets would trail long cables with multiple bombs attached to it which the enemy aircraft would run into and get tangled up in. Really, it was the wild west out there, and any idea was a possibility. But all of them had their problems, but radar’s problems was the easiest to overcome.

An important moment for Britain’s preparation for the Second World War would be the creation of the Committee for the Scientific Survey of Air Defence, or as it is more commonly called the Tizard Committee after its chairman Henry Tizard. The committee would have its first meeting in January 1935 and its goal was to determine the technologies that could best be used to bolster the air defense of the British home islands. They very rapidly made the decision to put their support behind the work on radar and to push forward its development with money and support. The first real set of experiments would take place using a short wave radio supplied by the BBC, and it was used to detect an aircraft flown by an RAF pilot. These very early tests were very simple, and in this case all the pilot was required to do was fly between a railway line and another point 20 miles away, and then repeat the process three times. During these tests it was very clear that radio echoes were bouncing back from the aircraft, and this would be the starting point of refinement for future efforts. By September 1935, the general capabilities of British radar were that they could identify that there were aircraft at about 15 miles and the elevation could be determined, at least roughly. However, there were inaccuracies that would take time to refine and iron out, and over the next several years the radar systems became both longer reaching and more accurate in terms of elevation and in determining the path that the aircraft was taking. But the interesting thing about radar, and something that many militaries would discover during the Second World War, is that radar is really just a tool, and it would be how that tool was utilized that would determine how effective it could be at defending against an enemy attack. For this purpose there were efforts made at taking radar, and the information that radar provided, and integrating it into the operational plans of Fighter Command and with the tactics used by its squadrons of fighters that were best positioned to use the information. This effort began in the summer of 1936, when a team was set up at Biggin Hill to work out the concepts and techniques of radar controlled interceptions, basically how they were going to use the information that radar was going to provide to actually shoot down enemy planes. Then the decisions that this team made were sent up to the head of Fighter Command Hugh Dowding later in 1936, who made the wise choice of implementing these strategies as the doctrine of the RAF Fighter Command to defend against enemy air raids, replacing the old wasteful standing patrols. The British were taking the first steps towards the combination that would prove so powerful during the summer of 1940, information about where the enemy was, and the practices and procedures to use that information.

The British were in no way unique in their investigations into radar though, and the Germans would do just as much research and just as much development during the 1930s. In many ways the radar capabilities of the Germans in 1940 were actually more advanced than what the British were working with, and their radar systems had better detection and fighter resolution. One of the important advantages they had was early research into the use of smaller radio waves, in the centimeter wavelengths, for the purpose, which would prove to be the most useful for the purpose during the war. To take advantage of this technology they would create a series of radar stations along the coast to warn them of the approach of any allied bombing raid. This system would be codenamed Freya and it would be used to create 8 radar stations for aircraft detection and then 3 surface radars would be used for naval ship detection. These radar stations would almost immediately prove their worth when on the second day of the war RAF Bomber Command sent a raid against the German naval forces anchored at Wilhelmshaven. The raid was detected but the Germans were unable to intercept the British bombers before they had dropped their bombs and were on their way back home. This was partially due to the fact that the Germans had not put enough emphasis on the operational side of radar during the years before the war. They had not done a great job of putting the processes and procedures in place to use the information that they were getting to the best of their abilities, they sort of neglected that entire area of investigation and refinement. The most important reason for this is that there was a kind of gulf between the German scientific efforts on radar and the military leaders that would be required to use the information, there was not the equivalent of that team at Biggin Hill whose sole purpose was to build out how the information would be used, although they were at always quick learners. When another raid was sent several months later the German fighters would use the early warning from the radar sets to exact a heavy toll on the British bombers with less than half of the British bombers making it home. It is also worth noting that the Germans knew that the British were working on radar, and the British knew that the Germans were, this was not really a secret technology, although the exact capabilities of another nation’s radar systems were not easily determined, it was know that they were being worked on. One thing that made it more difficult to determine the enemy capabilities is that, in these early days, everybody was using different radio frequencies for their radar systems, so it was not always easy to even find the frequencies that the other nation was using, particularly at a time when the range of the radar systems were so short.

While our focus during this series will be on the use of radar systems designed to detect enemy aircraft, there was also a huge amount of work going into the development and deployment of naval radar during this time. During the war naval radar would prove to be just as important to the course of naval operations was the shore based aviation radars were for airborne operations. The Royal Navy, as it so often would be before the Second World War, was the first to bring this new technology into operational use, although their systems were not as advanced as what particularly the Americans were building at that time. One of the challenges that the Royal Navy faced is that there was an emphasis among the British scientific teams to use as many off the shelf parts as possible, which would allow for the faster and cheaper creation of more radar sets that could be placed aboard ships. But this often meant that the equipment was just not as powerful as what could have been produced with more money and time, but those were both in short supply during the late 1930s. To make matters worse the majority of the British radar efforts were still being placed on air defense radar technology, which had a very different set of constraints when compared with naval radar sets. Most importantly size and power draw was not something that land based systems had to really be concerned about, they could be made much larger, and use a much larger amount of power. All of these challenges meant that the first naval sets, which would be put to the test in March 1937, were difficult to use, with range problems and general blindspots due to how they could be mounted aboard ship. But the utility was very clear, and advancement was quite rapid over the 3 years that followed. The Germans were working on naval radars as well, with their first naval radar set being mounted on the Deustchland class cruiser Admiral Graf Spee in 1936. Most of the German naval efforts around radar would askew air search radar in favor of surface search and fire control, which was primarily driven by what they saw as the threats that they would face in a coming conflict. The Americans and the Japanese would also have their own radar efforts, which would be on display in both positive and negative ways after the entered the war in 1941.

The end result of the British investments in radar during the 1930s would be the Chain Home system, which was really just the name for a string of radar stations that were put in place along the coasts to warn of German air raids. The Chain Home system was really built out of two different types of radar, the first to be introduced was the Chain Home radars which featured masts that were 360 feet tall and placed 180 feet apart. Between these two masts wires were strung, which would then be energized to send out the radio pulses, the echoes of which would be captured by 4 different masts that were 240 feet tall. This system did work but it had some limitations which would be important, the two most important was the direction of the radar and the altitude that they could detect aircraft. Because the entire system was based on fixed structures, it could only detect aircraft coming from one direction, which was not as much of a downside as you might expect because it was generally clear where the German air raids would be coming from, out to sea. However, it did mean that once the German aircraft moved out of the cone of vision of the Chain Home station it was up to either aircraft or spotters on the ground to keep track of them as they moved through British airspace. This is one of the reasons that coast watchers and the good old mark 1 eyeball were an important part of the British air defense network into the war years. The other problem was that it was possible for aircraft to fly under the altitude from which Chain Home could detect them, due to how the area covered by Chain Home interacted with its visible range. With perfect knowledge of the system, RAF pilots were able to determine that if they picked the correct spot between two Chain Home stations they could remain completely undetected as long as they remained under an altitude of 460 meters. To try and solve these problems a new series of stations were put in place, the Chain Home Low system. The Chain Home Low system had several advantages, most of which were because it used a higher frequency and involved antennas that could be shifted to different angles. Importantly for the overall structure of the Chain Home system it could detect aircraft at a lower altitude, which reduced the risk of German aircraft flying under the Chain Home’s ability to detect them. The structure of the Chain Home Low sites also involved transmitting and receiving towers. One of the interesting things about the towers for both radar systems is that they were open steel grid construction, so think of how the Eiffel Tower is built, that type of open steel grid system. This made them actually quite hard to actually destroy with German bombers, because there was not really that much that could actually be damaged unless by a direct hit, they were just really hardy structures. In terms of distance, the Chain Home system could detect enemy aircraft out to about 320 kilometers, or 200 miles, while the Chain Home Low system had a shorter range of only about 200 kilometers or 120 miles. There were three critical pieces of information that these radar systems could give the RAF. The first, and most obvious, was that there were enemy aircraft flying towards Britain, that was sort of the most important bit of info that they could possibly provide. The second was how large the group of aircraft was, although this was far from a perfect process and there was a large margin of error. The third, and just as important, was the altitude of the aircraft. This was a piece of information that was absolutely critical to the ability of the British to successfully intercept the raid, due to climb rate of aircraft during the Second World War, and the general importance placed on being above the target when beginning an attack. All of these pieces of information were worthless when it came to actually intercepting an enemy aircraft, because what the British needed was a way to actually use the information, that process we will cover in a later episode but it was why the entire system worked because it involved getting the information from the radar sites all the way down to the specific squadrons of fighters that were ready to leave their airfield. But next episode will be focused on the opposite problem that radar was trying to solve, because while detecting an inbound enemy raid was important, on the flip side it was also critical for the bombers to be able to find their targets, and that was actually a lot more difficult than you might expect, especially when the bombers were flying at night.