After the First World War, the major navies of the world had to try and determine what to do with naval aviation. But the development of carriers would be derailed by the Washington Naval Treaty.
Hello everyone and welcome to History of the Second World War Members Episode 27 - Aircraft Carriers Pt. 1 - What Are These Things? After the foray the member episodes have taken into diplomatic document conversations over the last few months I thought we would spend a bit of time looking at the evolution of Aircraft Carriers during the interwar period. The evolution of Aircraft carriers during this period is really interesting because they were trying to fill a role in naval combat that did not previous exist while also having to interact with the fact that aviation technology was rapidly evolving. One of the most important pre-requisites when trying to design aircraft carriers was determining what they would even be doing, and this was a more difficult question to answer than you might expect. It was just generally unclear what the best way to use airplanes were in relation to how naval battles occurred during and after the First World War. This was coupled with the fact that while trying to make decisions in say 1918 or 1919 about the future of naval aviation, the aircraft available for at the time were very limited in their capabilities. It was difficult at that time to see how such aircraft would meaningfully impact a naval battle like Jutland, and so the focus was placed on how the aircraft carriers, and the aircraft they carried could support the efforts of some of the other ships of the fleet, instead of focusing on how to replace those other ships. During this episode we will look at some of the early efforts by Britain, Japan, and the United States at creating aircraft carriers and their initial thoughts on how they could be used. Then over the next three episodes we will discuss how the technology and theory evolved during the 1930s.
Before we get into details of purpose of the carriers, and how their designs were adjusted to achieve those purposes, we should talk a bit about some of the design problems that would inherent with all carriers. First of all there were competing sets of priorities based on who you happened to talk to about carriers and their uses. If you talked to pilots, they really liked the flush deck carriers that some nations built after the First World War, these carriers did not have a super structure or traditional exhaust funnels that stuck out above the flight deck. This made the flight decks larger, but also removed any possible turbulence caused by that kind of superstructure which would effect take off and landing. If you talked to the people trying to actually manage flight operations and sail the ship, that superstructure sure made many things easier because the higher up sailors were positioned the easier it was to view what was happening on and around the ship. There were also major decisions to be made about how to alter ship design to accommodate the needs of the aircraft on board in terms of storage, maintenance, and flight operations, while also not compromising the ship part of being an aircraft carrier. All of this resulted in quite a bit of trial and error among all of the nations who built carriers during the interwar years. It also resulted in a lot of evolution of design one generation to another during this period, and some pretty important differences between nations in terms of how they balanced and prioritized the various concerns that had to be accounted for in the designs.
One of the challenges was also just a decision that had to be made before any other: what exactly were these carriers going to be doing? Until the last years before the start of the war the aircraft on board of the carriers were not powerful enough to be decisive on their own, and so the role of aircraft carriers was all built around the idea of how they could support what were seen as the decisive naval group, the battlefleet. The British initially focused on two different types of carriers, one designed for reconnaissance, with an emphasis on speed and range, and another that de-emphasized speed as it was designed to accompany the battlefleet and to provide spotting for the battle line. The American and Japanese designers generally focused on what the British would consider the faster reconnaissance designs, due to the much greater emphasis placed by those navies on finding the enemy fleets in the vast distances of the Pacific. Pretty much all carrier design begins from these basic ideas and then goes through a series of very obvious evolutions, or at least very obvious in retrospect. They start with the goal of keeping reconnaissance and spotting planes up in the air and able to move around the air above a naval battle. The next logical step is a desire to prevent the enemy from finding your fleet from the air, and then also preventing their spotting aircraft from being able to effectively direct fire. The only real way to do this is to start placing fighters on carriers, they can provide protection for your spotting aircraft as well as threaten enemy spotting aircraft. All of this would, in theory, work quite well, but there was still a problem. If you wanted to put fighters on the carriers to prevent the spotting goal from being achieved, the enemy could do so as well. The next logical jump was made in the late 1920s and early 1930s, and that leap was that the only way to really secure the airspace above the naval battle was to actually seek out and sink the enemy carriers. It was only after the enemy carriers were destroyed that your spotting aircraft would be safe, and this focus on attacking the enemy carriers would drive much of the carrier and aircraft design in the late 1930s. I find it interesting that it is this shift in the view of what carriers should be doing that ends up making carriers so dominant during the Second World War. Trying to sink an aircraft carrier is not that much different than trying to sink any other capital ship. Obviously a battleship and a carrier are quite different in design, but the best tools to actually attack and sink them from the air are not that much different. Torpedoes and bombs are still the best options, even if they vary slightly in effectiveness between the two different targets. And so while the push was being made to create faster and more powerful aircraft with the goal of sinking enemy carriers, the tools were also being put in place to sink any large enemy ship, even if the belief that capital ships would not be put out of action from air attack would persist up to the war years.
When thinking about attacking other carriers, or any other ship really, there were two options that were seized upon very early as the best way to inflict damage: bombs and torpedos. Bombs were one of the earliest weapons used by aircraft, and it would almost instantly be seen as something that could be used to attack surface vessels. There were two major problems with attacking ships with bombs: armor and size. Unlike many of the targets for aerial bombing on land, many targets at sea were designed to be hit by explosive shells. This meant they had armor and other protections to help protect them from damage received from explosions. This is one of the reasons that there was some doubt that air attack could seriously threaten something like a battleship, they were designed to be hit by naval shells that weighed almost a ton! Aircraft would eventually be able to carry large enough bombs, but then there was the problem of hitting the ships as well. There were two schools of thought around bombing, one was that ships could be hit by large level bombers dropping a large number of bombs from a relatively high altitude, the reason that this seemed possible was due to the same reason that strategic bombing advocates believed that strategic bombers could hit specific targets on the ground, just a general massive overestimation of the ability of bombers to put their ordinance on target. This would prove to be the biggest problem for level bombing of naval targets, as would be proven time and time again early in the Pacific war when Japanese ships easily dodged attacks from American B-17s. This problem could be solved through dive bombing, which would allow for a far more precise application of the bomb onto the target, but dive bombing at the speed required, and with a large enough bomb, would not really become possible until the mid 1930s. Eventually it would be very deadly, especially against other aircraft carriers in the Pacific, due to how it was able to take advantage of the most vulnerable area of Japanese and American carriers, their unarmored flight decks. Dive bombing was also seen as a great way to attack carriers because even if a bomb hit did not sink the ship, or even really cause major damage, a bomb hit on the flight deck could still force a carrier to cease flight operations, which in the short term was just as good as sinking it. The other attack option that was pursued was around the torpedo. Interest and research into aerial naval torpedo predated the First World War. At that point the torpedo was a well known weapon, launched from either surface ships or submarines, but there were some new challenges that had to be solved if they were to be delivered via aircraft. The first problem was size. The torpedo had to be downsized so that it could be carried on the aircraft of the 1920s while still retaining enough explosive payload to cause sufficient damage. This was actually the easy part. The more difficult challenge was solving for all of the new stresses put on the torpedo when it was air launched rather than from a ship or submarine. Naval aircraft on attack runs would be taking anti-aircraft fire, and so the faster they could fly, and the more they could change their elevation, could result in greater survivability. But as speeds increased the impact force when the torpedo hit the water also increased, which required the structure to be strengthened. It was also important that the torpedo fly straight before it hit the water, and then swam straight in the water, two requirements that had to be balanced in the design and which would take some time to solve for correctly. Both of these weapons would eventually be largely solved for, although there would still be some reliability issues for some models when the war started.
While there were many changes for the targets of the planes on a carrier, there were also many design decisions that had to be made around how to actually deal with the fact that suddenly there was a new type of ship that had to store and operate as many aircraft as possible. The decisions around how to store and operate aircraft resulted in some really interesting differences between nations that would have ramifications in both design and wartime performance. For example, on American carriers the flight deck was used as much as possible for servicing and rearming aircraft. This meant that aircraft were parked on the deck, they were warmed up there, armed and fueled there, and then they would take off. The Japanese on the other hand preferred to do as much as possible in the aircraft hangers below the flight deck, which meant that fueling, arming, and engine warm ups were performed below decks. This put a smaller limit on how many aircraft could be based on each carrier, because they were limited by the smaller hanger space. The benefits of doing all of this in the hanger was making it easier to transport bombs or torpedoes to the aircraft, far less disruption of flight operations while servicing aircraft, and it being generally safer to perform the operations in the hanger. However, in retrospect these benefits were probably not worth the reduced aircraft complements that were forced on the Japanese carriers, and the British carriers that followed a similar policy.
In general for each of the three nations we will be focusing on today, Britain, Japan, and the United States there were three generations of carriers built before the end of the Naval Treaty System in 1936. These general break down into the first carriers built after the First World War, the Naval Treaty conversions, and then the generation built in the late 1920s and early 1930s under the provisions of the Naval Treaty itself. The first generation of carriers were the British Hermes and Japanese Hosho, . Both of these carriers were purpose built, so they were designed to be carriers from the very beginning and they were generally quite small by later standards, with the Hosho being the smallest at just above 7,500 tons displacement. At roughly the same time that the two carriers were built built and commissioned the United States navy would convert the collier Jupiter into the Langley, its first aircraft carrier. There were some really interesting features of these early carriers, the most noticeable of which were the deck guns that would be tested on the ships. During these early naval aviation efforts there was always the feeling that the guns might still be required due to the number of aircraft that could be carried, the fact that those aircraft were primarily designed for reconnaissance, and the speed of the carriers which were easily outpaced by destroyers and cruisers. These concerns resulted in the British and Japanese putting 8 inch guns on the Hermes, although it would be found that the guns caused some problems with flight operations and just in general took up too much space. Surface guns would eventually go away, although they would also make an appeared on other carriers during the interwar years, but they point to the kind of uncertainty about what the future held for naval aviation and the war at sea. This was still combined with the thought that in the early 1920s airpower just was not at a place where it could realistically threaten large capital ships at sea, and that probably would not change in the future. At the same time it was recognized that aviation would take on growing importance in the war at sea. For example here is a quote from the ‘Future Policy Governing Development of [an] Air Service for the United States Navy’ which was put together by the United States Navy General Board in 1919 at the conclusion of a number of hearings on the future of naval aviation. In this report, the requirements of naval aviation would be described as ‘To ensure air supremacy, to enable the United States Navy to meet on at least equal terms any possible enemy, and to put the United States in its proper place as a Naval power, fleet aviation must be developed to the fullest extent. Aircraft have become an essential arm of the fleet. A naval air service must be established, capable of accompanying and operating with the fleet in all waters of the globe’.
After the first generation of very experimental carriers, where it was still pretty clear that everybody was trying to sort out what these carriers were and what they would be doing the Washington Naval treaty would arrive and shake up everything. The primary impact of the Washington Naval Treaty on carrier development actually had nothing to do with carriers but was instead the limits placed on capital ships of the battleships and battlecruiser varieties. The limits on battlecruisers and battleships resulted in a situation where both the Americans and Japanese had battlecruisers that were somewhere in the production cycle that they would choose to convert into carriers, because they did not have the tonnage available to complete them as battlecruisers. The British would convert ships that were already completed and had seen action during the First World War. This generation of carriers are also interesting because they would play a major role in the war, any student of the Pacific theatre of the war will recognize the names of the four converted ships: Akagi, Kaga, Lexington, and Saratoga and in the Royal Navy the Furious, Courageous, and Glorious. These ships would all be heavily altered from their initial configurations before the start of the war, but the ships were the same. I think the best way to look at these carriers is to look at their designs all together, but based on topic. Starting with the American converted ships, when they were completed there was som concern that they were both too large. At the time thee United States and Royal navies weree only allowed 135,000 tons worth of aircraft carrier tonnage, and their battlecruiser conversions were dictated in size by the battlecruisers they were based on, for the Americans it meant that the Lexington and Saratoga, both at 33,000 tons, took up half of that limit. For the British it meant that the three converted carriers, each of 24,000 tons took up roughly the same. There were some in the American Navy and at the Naval War College who favored smaller carriers, which they felt gave the Navy a greater ability to project power while staying under the limit. This would go onto inform the design of the USS Ranger, which was less than half the size of the two converted ships. For the Japanese the two converted carriers took up an even higher percentage of the available space, with a total of 54,000 tons between them, this was because Japan had a lower total displacement at just 81,000 tons. This would cause the Japanese to make their next carrier also a smaller version, much like the Ranger, with the Ryujo being just 8,000 tons of displacement. Sizes would fluctuate over the course of the following 2 decades, but it is probably somewhat informative to say that the size of the converted carriers would not be exceeded until the Americans built the Midway class and the British built the Audacious class during the late war years. This is indicative of two things: converted battlecruiser hulls were not the most efficient ways to design an aircraft carrier, and there was the belief that it was probably better to have more, but slightly smaller carriers rather than fewer and slightly larger.
Perhaps the more interesting feature of the British and Japanese converted carriers were the fact that some of them featured multiple flight decks. In the Japanese Navy the Akagi and Kaga would be under construction for most of the 1920s, and they were both test beds for Japanesee carrier design. For example Akagi would be a flush deck carrier, so one without any kind of tower or superstructure, and would also feature a multiple flight deck arrangement. The theory behind having multiple flight decks is that it would allow the full complement of aircraft on the carrier to be launched in the shortest possible time. The cycle time required to launch aircraft was an important factor in the evolution of how nations used aircraft carriers, and something that could only really be worked on after carriers came into operation. These multi-deck carriers were based on the idea that it was important for a carrier to be able to launch and land aircraft at the same time. This was more important in the 1920s when the endurance of the aircraft was less, and was made possible by the fact that take off distances for aircraft were reasonably short, which meant that the bottom flight deck still had enough length to allow take off even with its shortened length. The Akagi took this concept to its zenith by having not just one but three flight decks. The top deck was 190 meters, spanning the entire length of the ship, the middle deck was just 18 meters long, which was only really useable by the lighting aircraft which were generally fighters or observers, then there was a third deck that was 49 meters long which could be used by torpedo bombers. The concept was interesting, and did allow for faster flight operations, but it was also completely unworkable as aircraft grew larger, and during the 1930s all of the multiple-deck carriers would be reworked to just have one large flight deck. While all of the battlecruiser conversions would have experimental features, they were absolutely critical for all three navies due to their ability to give them the ability to practice and exercise with actual carriers and actual carrier aircraft. For a weapon system like the aircraft carrier, that was such a new and different tool just the time to work with carriers, even if they had some design choices that would be undone in later carrier designs.