When World War II broke out in 1941 with Japan surprisingly attacking the United States’ main Pacific Naval Base at Pearl Harbor, the Japanese possessed the largest and most powerful aircraft carrier force in the world. Added to the sheer numbers of carrier platforms, the Japanese had developed the world’s largest and most complete naval air fleet. This was the arm of the military that Japanese Imperial officers believed would win the war for them. A thought augmented by the early streak of quick victories enjoyed by the Imperial Navy. These successions of quick conquest also gave the Japanese military the false hope that they could maintain their initial numerical advantage in deployable carriers over the US for a long run. An advantage that was hallowed when the war commenced and one that would last only a few months. The reality was that, although Japan outgunned the US and Great Britain in deployable flatbeds, they were not prepare to engage the US and, later, the UK in a battle of attrition. It was this attrition, and the fact that they could not replace their lost carriers or even more importantly, their experience aircrews; as promptly as the Americans could, that lead to the downfall of Japan’s carrier force.
Japan entered hostilities against the western democracies with the most powerful and flexible carrier force that world had seen. Seven completed fleet carriers (Hosho, Akagi, Kaga, Ryujo, Soryu, Hiryu, Shokaku, and Zuikaku) formed the backbone of the Imperial Navy’s power projection force. They also possessed the most experienced naval aviators in the world. It was this numerical as well as tactical advantage the made possible Japan’s early surge into the Pacific Theater. At the end, Japan lost all of those carriers, with the exeption of the Hosho, in combat operations during the war. These losses were hard to overcome by a relative backward industrial society such as the one Japan possessed. During the war, Japan only managed to design and develop four additional fleet carriers, while its main adversary, the United States managed to build 17 front line fleet flatbeds. It was this fact that spelled the demise of the Japanese Navy in WWII.
It is the intention of this article to paint a clear picture of the development and conception of the Japanese flatbeds fleet during the war with the US. The article hopes to leave the reader with detail information on all the Japanese aircraft carriers developed and deployed between 1941 and 1945. It will make emphasis on the carriers’ developmental history as well as their combat operations, right to the end of their service lives.
A Brief History
The Japanese carrier development program before the Great War resembled those of the United States and the U.K. Their view of sea-based aircrafts flying aloft for hours was perceived to be for strategic as well as tactical reconnaissance operations only, thus no new advantage could be gained by constructing a vessel to operate airplanes only. Big guns still dominated their ideas, same as in the US and Britain. It was not until late in 1912, when Japanese official embedded, with Royal Navy forces, began to seriously consider the seaplane tender ship as an offensive platform instead of just another recon unit. With this in mind, in mid 1913, a major conceptual experimentation took place within the Imperial Japanese Navy confines. They were able to re-fit an old transport ship, the Wakamiya Maru, with two seaplanes extenders. In the fall of that year, the floatplanes operating out of the Wakamiya participated with the whole Combine Japanese Fleet in maneuvering and detecting exercises. The outcome of the exercises was impressive. The Wakamiya was able to located and engage most of the over-the-horizon targets assigned to its zone of operations without the “sea-plane carrier” being spotted by the Fleet’s screening ships. Trials continued trough the early months of 1914. Again, the seaplane tender demonstrated a unique ability to project power beyond its visual engagement range. In late 1914, faith intervened to push the nascent Japanese aircraft carrier program one step closer towards achieving operational status: the War to End All Wars erupted in Europe.
In an attempt to display their newly acquire naval power, Japanese leaders decided to extract territories from the overextended Imperial German forces in the Pacific, they wanted German-held territory in the south west coast region of China. The Wakamiya was dispatched as part of a Japanese fleet element assigned to capture ports and facilities in the Chinese coast. Meanwhile, Japanese observes and naval liaison officers attached to the British Royal Navy began reporting on the British employment of sea-tendered aircrafts to spot and track German ships, especially U-boats, operating in the North Sea as well as the Atlantic Ocean. These reports, as well the Japanese Navy’s own experience with the Wakamiya, enabled Japan to formulate a new strategic vision for its main fleet that incorporated the carrier as one of its main features, instead of just using it as a complementary platform. In the 1918, as well as in the 1920 budget, Japan allocated a major portion for their Navy design and development funds into their carrier platforms. This decision was augmented by an agreement with the UK, where the former would render technical assistance to the Japanese in exchange for some basing rights along the Hong Kong sea route. The British assistance centered on naval aircraft profiles and combat tactics. Faith again intervened when in 1922 the Washington Naval Treaty provided a structural limit on the size of the world’s top naval powers. The new treaty also provided the guidelines for displace characteristics of new ships designs. A limit of 27,000 tons was placed on all of the signatories. Any ship under construction above those limits was permitted but up to 33,000 tons. The tonnage aspect relating to carrier vessels was established at 81,000 for Japan, a deficiency of 54,000 tons from their US and British counterparts. It was this limitation that historians had attributed as one of the causes of Japan’s bellicose behavior towards the US since the early 1930s. It’s worth pointing out that during the Japanese binding to the Treaty’s tonnage limitation they were continually circumventing the tonnage issue in an effort to maintain parity in carriers with America.
There’s another, more important point to be made about how the Japanese Navy interpreted the Treaty’s ramifications on its carrier program. Before Washington 1922, Japan was a forerunner in the development of combat tactics for carrier platforms. They were one of the early converts to carrier power projection, but they still relegated the carrier force as a second fiddle to the big guns of the once mighty battleships. The Treaty, with its overall tonnage limitation, was the turning point in Japan’s carrier program. From that moment on, Japanese leaders decided not to augment its existing fleet of battleships, instead, the carriers would become the center piece of a newly designed Imperial Navy. Japanese leaders knew that they could not match ship per ship the US, but with a numerical as well as tactical advantage in deployable flatbeds, they believed that they could, not only offset the US numerical superiority in capital ships, but in fact take the strategic advantage away from the Americans in the vast Pacific Ocean. The new strategic position adopted by Japan in direct response to the new realities imposed on it by the 1922 accords meant that their main axis of attack would originate from its carriers force instead of the traditional battleship alignment, thus, from that moment on the carrier became Japans main first strike weapon system. As such distinction merits, all available naval resources were, either placed on the carrier itself or allocated to the development of the carrier’s air complement. Capital ships like battleships, heavy and light cruisers still received a substantial amount of the budget, but the importance of the Japanese had cleared shifted to their new first strike platform: the aircraft carrier.
1. Taiho Class (Great Phoenix)
The Taiho had the distinction of being Japan’s first carrier to be fitted with a redundant damage control system that would had enable the flatbed to operate at the same profile even if she was damaged. Taiho was also the first carrier developed by Japan to incorporate an armored flight deck area. The deck’s thickness was in the range of 75 to 80mm. The Japanese believed that this level of reinforcement would have allowed the deck to withstand hits from up to 1,000lbs of free fall bombs. An armored belt of 5.9″ circled the hull structure. But, as with most of Japan’s other carriers design, the Great Phoenix lacked armored platting hangars, a design flaw that would prove to be fatal for the entire carrier fleet. Taiho design was comparable to that of the famous Shokaku-class, except that it incorporated a large Island structure similar to that founded on the original Hiyu design. The other major departure from the Shokaku design was that the Great Phoenix’s bow was enclosed instead of the open air bow on pass vessels. This was done in order to provide the Taiho with an improve sea going capabilities. This new bow arrangement allowed the Taiho to have a more robust (33%) hangar space available for ordinance and fuel storage. The Great Phoenix was designed with a low center of gravity to improve the ship’s seaworthiness. As a result, the carrier had only to hangar elevators, one in the aft and the other in the forward area. With only two designated hangar areas available, the Taiho did packed an impressive cargo of aircrafts. Up to 75 front line plus 10 reserve aircraft could be embarked on the ship.
The new aircraft carrier was fitted with the newly designed Type 98 antiaircraft (AA) gun. This new gun was a 100mm demon that can shot at ranges up to 21,300 yards. Six dual mounts housed three of these awesome guns on each side of the hull. Seventeen of the triple 25mm guns were placed around the flight deck as well as in the Island superstructure. The Taiho also carried the two of the new Japanese Type 21 radar array. One was paced atop of the island while the other lay in the lower aft section of the structure. Taiho was completed in March 1944 and immediately was transferred to the Imperial Navy’s Mobile Fleet based at Singapore, where it was assigned to take over the flag of the Mobile Fleet.
|Top Operational Speed||33 knots|
|Combat Range||10,200 nautical miles|
Taiho first extended combat action saw her launching strike aircrafts against a US carrier fleet in the morning of June 19th, 1944, when she was hit by one torpedo from the USS Albacore. Originally, the officers of the Taiho though that the hit was superficial and that the carrier would be able to sustained until it reached port, but in reality, the impact was more profound. The impact wave of the hit cracked the main aviation fuel tanks in the forward elevator area. As the fuel began to mix with sea water, the carrier’s crew demonstrated their under training in damage control tasks, a weakness that had already proven fatal to many of their companions in other flatbeds. They opened all hatches around the ship’s two hangar areas in an attempt to steam the water flow. It was to no avail. Because just four hours after the impact, the damage control crew turned on all of the hangar’s extractor fans thus setting up a massive explosion the blew the sides of the hangars. At this moment, the resulting fires began to consolidate and a second, most violent explosion shook up the ship. The hull was compromised and power was lost. Two hours later, the ship buckle under its own weight finally sinking with around 400 men trapped below the rupture deck.
2. Unryu Class (Unryu, Amagi and Katsuragi)
The Unryu class had the distinction of being Japan’s last front line carrier design of the war. The Unryu was a departure from the advance Taiho class. With this class, Japan returned to its original carrier designs roots. Speed above armor and protection was the rule instituted on the Unryu. The Unryu class was an attempt to match carriers with the US. In fact, the whole class was a crash curse on carrier construction. In 1941, the Navy ordered the development of six new flatbeds as soon as possible. The time requirement prevented Japanese shipyards to maximize what they had learned on the Taiho and Shokaku classes. To maximize their construction, all of six the carrier’s proposed on this class were designed along the lines of the Hiryu class. The first three hulls were laid in mid 1942, while the next three were to be under construction by the autumn of 1943. Those three never made it out of the yard. When the program was terminated in the spring of 1945, these three units (Ikoma, Katsuragi and Kasagi) were nearly a three quarters up. There were initial speculation that if the class was able to perform adequately, eleven additional units would have been ordered.
The Unryu class boats possessed almost the same hull structure, armor plating and hangar space distribution of the Hiryu. Their only structural difference was the Island placement. In the new class, the Island was located forward on the starboard side of the ship. As with others Japanese carrier designs, only two elevators were fitted to the boats. Two main hangar areas were able to storage 57 operational planes with seven reserved units as backup. The carriers of this class were armed with the same Type 89 guns as in the Hiryu boat. Three of the 89s were placed on each side of the carrier’s upper hull area. Sixteen triple and three single fire 25mm antiaircraft guns were also fitted around the flatbed’s superstructure. An additional four triple and thirteen single 25s were installed, giving the Unryu class an impressive array of 76 AA guns. The class was also the first of its kind in Japan to carry six 28 barrel 4.7″ rocket launchers for short range action. Another distinction for the carriers was that they were the first platforms to be incorporated with a radar system since its design. Two of the Type 13 radars arrays were installed. One at the island’s mainmast and the other on the four hinged radio antenna.
|Total Displacement:||17,150 tons Unryu
17,260 tons Katsuragi
17,460 tons Amagi
|Top Operational Speed||34 knots (Katsuragi 33 knots)|
|Combat Range||8,000 nautical miles|
Of the three completed ships of the class, only one actually saw active combat. And that action only involved the ferrying of aircrafts and ammunition to the Japanese garrison in the Philippines during the last stages of the war. Unryu, the lead boat, was commissioned in August 1944 and immediately was assigned to the Mobile Fleet. In December she was tasked to carry airplanes into Manila Harbor. On the 9th, while in transit to the Philippines, the Unryu was spotted by the submarine USS Redfish. The Redfish proceeded to put two torpedoes into the port side of the carrier hitting the half-filed aviation fuel tanks. The ensuing explosion sent the boat to the bottom with nearly 1,350 of its crew compliment. The other two carriers, the Amagi and Katsuragi were commissioned in October 1944. Neither embarked on any ocean going travel, mostly because of Japan’s massive fuel shortages. In March 1945, the Amagi was lightly damage in an American raid on Kure. On July 25th, a more intense bombardment damaged the Amagi’s hull integrity and she sank within minutes. Amagi had the distinction of being the last Japanese carrier sunk in combat. Katsuragi, who also received heavy damage during the 24th raid, survived the war. She was issue to the Allies as reparation payment and was ultimately scrapped in the fall of 1946.
3. Shimano Class
The largest carrier built during World War II, Shinano would remain the biggest flatbed in the world until the US Navy deployed its first series of super carriers in the 1950s. Shinano was original conceived as the last of the Yamato class super battleships. Laid in May 1940, work of the battleship stopped by June 1942. In August the Japanese Navy decided that the era of the big gun wagons was over and, still coping with the losses suffered at Midway, decided to convert the Shinano to an aircraft carrier. Work on the conversion started in September. At the time, Japanese naval leaders envisioned a new role for the huge hulled ship: floating fortress. The Shinano would become the next step in the evolution of the aircraft carrier, Japanese commanders thought at the time. Aircrafts from small decked carriers as well as long range land based planes would use the Shinano as sort of refueling and re-supplying platform. Thus in the design of the ship’s structure, only one hangar deck area was implemented. This reduced the amount of planes, 47, that new flatbed could carry. These planes were primarily for self defense purposes.
The Shinano’s design closely resembled that of the Taiho’s. The ship’s was fitted with an armored flight deck of three inches. Two elevators served the hangar area which was divided into two separate compartments. The forward hangar area was only covered by shutters, while the rear area was completely enclosed. A huge island structure, with a slanted stack, was placed the same way as in the Taiho’s. A massive armored belt, over eight inches in thickness, covered the other hull area. Additional armored platting, 7.5 inches worth, was installed on the machinery and magazine’s areas. Two pairs of Type 89 AA were placed on the forward and rear areas of each hull side. Between 30 and 33 triple 25mm guns were mounted all around the deck area. Twelve short range rocket launchers were also added. Two Type 21 radar systems were placed on the ship. One in forward area of the island and the other in the aft. These were augmented by two additional Type 13 arrays. One installed on the mainmast and the other on the forward port side of the radio antenna.
Carrier Profile Characteristics
|Top Operational Speed||27 knots|
|Combat Range||10,000 nautical miles|
Apart of being the largest carrier built at the time, Shinano had also the distinction of having the shortest life span of any carrier in WW II. Commissioned in the morning of November 18th, 1944, Shinano departed the Yokosuka docks on the 28th for final fittings at Kure. On the early hours of the 29th, she was torpedo by the USS Archerfish. Although the damage was not considered sever, the ship did not had its full complement of counter flooding and damage control systems. As the ship continued its voyage, the flooding, checked by the crew at first, began to overmatch the ship’s countermeasures. Power was lost and after eleven hours, the mighty ship capsized tanking with her 1,350 crewmembers.
In the end, Japan felt victim of what the saw before the war commenced as its biggest weakness: their small industrial base. Of the three carrier classes developed during the war, only the Taiho’s and Shinano’s represented any real opportunity. One, the Taiho, was not properly exploded mostly because Japan could not build them in numbers; the other, Shinano, although very promising, became irrelevant due to its late entry into the war. The Unryu class was Japan’s last attempt at matching the Americans in carriers. They were easy to mass produce because of its simplicity of design. This same trait also worked against them. By the time the class was ready for action their boats were easily outclassed by the new American flatbeds.
It was Japan’s lack of industrial material, know-how and experience work force that accounted for the small number (only five ships were developed) of new carriers during the war. In contrast, the United States developed and deployed 17 front line carriers during that same period.
Warship International, Volume 1, International Naval Research Organization, Holden 1982
Aircraft Carriers, David Brown, Arco Publishing Company 1977
The Imperial Japanese Navy, BG Gordon & AJ Watts, MacDonald 1971