The third giant of carriers
In December 1941, the Imperial Japanese Navy (IJN) possessed the second largest carrier fleet worldwide, with 9 of these in service, IJN Hosho, Kaga, Akagi, Hiryu, Soryu, Ryujo, Shokaku, Zuikaku, and Zuiho. This represented 212 330 tonnes. It must be compared to the Royal Navy’s 12 carriers (Argus, Eagle, Hermes, Furious, Glorious & Courageous, Ark Royal, Illustrious, Victorious, Formidable, Indomitable, and Audacity) representing all together 239,450 tonnes, and the US Navy’s eight carriers (Langley, Lexington & Saratoga, Ranger, Yorktown, Hornet & Enterprise, Wasp) so “only” 177,100 tonnes. So not only the IJN carrier force was 1/3 larger than the US Navy’s but Japanese pilots were among the best experienced and trained of all belligerents with an ongoing campaign in China since 1937, and had another ace of their sleeves, the best naval fighter of its time, the Mitsubishi A6M “Zero”. It’s then not a surprise the IJN did so well until mid-1942, and also how much the USN effort to resist the onslaught until that point was meritorious.
Development of IJN carriers history
The IJN’s love affair with naval aviation came a long way. It started in fact in August to October 1914 when besieging the German colony of Tsing Tao. Planes provided useful informations, strafed enemy troops and ships, and even duelled with the sole German plane in the area. The close bonds between the Royal Navy and IJN allowed officers to made exchanges onboard British ships and they were well informed about British developments in early conversions as aircraft carriers, most notably the Furious. So when the British admiralty started the HMS Hermes on plans in 1917, laid down specifically as an aircraft carrier, Japan was not long to follow. The Hosho however, was completed before, and became the world’s first operational aircraft carrier, built as such.
Japan had to comply with the Washington disarmament treaty and peace conference, despite its protestation of a lower authorized tonnage than the two largest navies of the world, on each side of the Atlantic. The treaty forbade battleships and battlecruisers and obliged many new constructions to be scrapped, but in the spririt of the time, did not yet recoignised the potential of naval air warfare and considered at best aircraft carriers as mere auxiliaries of the fleet, alongside seaplane carriers and tenders.
Therefore, yet again informed of the other fleet’s decision about their unfinished capital ships, the Japanese admiralty devoted the conversion of two of her most advanced cancelled capital ships, the Kaga and Akagi.
The Kaga as delivered, showing her amazing three-staged flying-off decks.
At the time of poor capabilities of planes against battleships, it sounded logical to keep the strenght and armament of capital ships in aicraft carriers, having barbette guns and armour made therefore a guarantee of self-defense against any incoming naval threat. AA was anecdotal. The early completion of the Kaga and Akagi, in 1927-28 was assorted yet of many experimentations in launching and recovering planes on separate decks for example. Control could call for popup bridges or small ones.
Development of IJN air service and carriers
The Imperial Japanese Navy Air Service or 大日本帝國海軍航空隊, “Dai-Nippon Teikoku Kaigun Koukuu-tai” abbreviated IJNAS was funded in 1912, as the same time as the conversion of the Japanese seaplane carrier Wakamiya.
About the Wakamiya
The role of this seaplane carrier could not be underestimated. The whole lineage of the IJN aviation proceeded from there. The Japanese fleet air arm originated in 1912, with the creation of a Commission on Naval Aeronautical Research (Kaigun Kokūjutsu Kenkyūkai), a subdivision of the Technical Department. The commission was to promote aviation technology and training and at first centrated on non-rigid airships, before swapping to aircraft. This was followed by purchases abroad, and send junior officers also to be trained in the West. The navy’s first seaplaned were Glenn Curtiss models and two Maurice Farman. Three officers were sent to Hammondsport (Curtiss) and two in France for training and instruction, making back home their first flights at Oppama, Yokosuka Bay. The smae year, the Royal Navy created the Royal Naval Air Service, soon inspiring Japanese admirals, which proposed to rename their own naval service. In late 1912 operational use started, and in 1913, the Wakamiya Maru was converted into a seaplane carrier. At first it could carry two assembled and two disassembled seaplanes and soon took part in naval maneuvers off Sasebo.
The Imperial Japanese Navy Air Service
WWI developments of the IJNA
The beginnings of Japanese naval aviation in 1912 found a first concrete application on 23 August 1914. As a result of its treaty with Great Britain, Japan declared war on Germany, and they soon blockaded the German colony of Kiaochow, and its administrative capital, Tsingtao (Shandong peninsula). This siege saw the use for the first time in history of naval aviation, ship-borne. From September 1914 the four Maurice Farman seaplanes from Wakamiya multiplied reconnaissance missions and starting strafing and bombing German positions as well, as well as the ships. Crude bombsights where installed and the six to ten bombs were just converted shells released through metal tubes installed either side of the fuselage. On 5 September, they bombed the Bismarck battery, a key point on Tsingtao’s fortifications. They also confirmed the SMS Emden was absent, passed to British intelligence. On 30 September Wakamiya was in turn damaged by a mine and left her seaplanes behind as she departed for Japan for repairs. Her seaplanes went on harassing the Germans until the German surrender on 7 November 1914, with 50 sorties and 200 bombs dropped.
Ro-Go Ko-gata operating from Hosho. In the eearly days, the IJN carrier operated both seaplanes and land planes.
In 1916, the Commission on Naval Aeronautical Research was disbanded, but funds were reallocated to three naval air units (called “hikotai”) under supervision of the Naval Affairs Bureau of the Navy Ministry. The first one was created in Yokosuka in April 1916, but its activity was limited to operate with the fleet for every manoeuvres nearby with its few seaplanes. In 1917, officers at the Yokosuka Naval Arsenal created the Ro-Go Ko-gata, by all account the first IJN reconnaissance seaplane. They replaced with ease the obsolete Maurice Farman used up to that point. It became the mainstay of the IJNA until the end of the war and beyond, retired in 1924-25. Manufacturing followed a simple path of reverse-engineering foreign built planes, engines, wings and fuselages. This path was followed nearly up to WW2, and French, American, British and German models were purchased all along the interwar in small quantities, with the exception of licence-built models. The 1918 naval expansion program helped creating a true air group and dedicated naval air station at Sasebo.
Facilities were constructed at Lake Kasumigaura (Ibaraki Prefecture) near Tokyo, which operated both naval and land planes. Naval air training was transferred there, and it stayed until WW2 the IJNA academy. Also Japanese officers were invited to assist demonstration of HMS Furious in 1918, and probably informed of a new dedicated carrier just ordered, which led to secure the addition of a carrier in eight-eight fleet program that same year. IJN Hōshō was the result of this, laid down in December 1919 at Yokohama, and second carried designed from the keel up after HMS Hermes but completed sooner.
Creation of the carrier arm (1920-28)
In the mid-1920s, land based seaplanes dominated the IJN air arm, used for reconnaissance and ASW patrols. An ambitious plan of creating 17 squadrons was planned, thwarted by budgetary constraints, and by 1931, only eleven were operational. The Washington Naval allowed Japanese to request two incomplete capital ships to be rebuilt as carriers, the IJN Akagi and Amagi. Amagi was however damaged during the Great Kanto earthquake in 1923 and so badly damaged she was dismantled. Instead, Kaga was her replacement, converted yet from another cancelled class. That’s why the Japanese could not replicate the USN conversion of the Saratoga class. One was battleship-based, the other battlecruiser-based and they differed considerably in design. IJN Akagi was eventually completed in 1927 and Kaga in 1928, but with the Hosho, this gave the IJN a way to create and experiment new doctrines and operating procedures.
In 1928, indeed the trio led to the creation of the First Carrier Division, studying naval air engagement possibilities. However due to their planes short range the hierarchy was still thinking in terms of observation for the fleet. As in other navies, it was seen as a support for the main battle fleet, not an independent striking weapon. In addition to spotting exercises, plnes were to lay smoke screens to protect their own, and provided air defence for the fleet as better fighters were available. However, between news of Mitchell’s experiments in the US and more powerful engines, it was now possible to carry out torpedo-bombing missions with confidence and integrate more offensive roles to the carrier division.
The shift to a carrier-first strategy (1936)
IJN Hosho off Shanghai in 1937. Like the legion Condor over Spain for Luftwaffe’s future officers, combat over China gave considerable experience and confidence to IJN pilots
This was pushed by naval aviators, arguing they needed to win the aerial engagement to clear space over the opposing fleets before final surface battle, notably to elminate the enemy’s own spotters. They also soon advocated the enemy’s carriers were to be main targets of naval air power. Because this divergence lasted between a large part of the traditionalist officers and these new generation of pilots officers (with a certain Yamamoto acquired to these ideas), there was no unified doctrine. But in the 1930s, many air strike at targets beyond the range of the fleet’s guns demonstrated the potential of a new generation of carried-borne attack planes. At that stage, torpedoes were still preferred. Until the Japanese were introduced to the co,ncept of dive bombers, it had low priority. In the end, gunnery staffs (used to work with spotter planes) joined naval aviators, to ask a doctrine around a pre-emptive strike was crafted. It was to achieve air superiority to prepare the surface battle, in 1932–33.
The shift away from battleships as main target to the aircraft carriers was apparent in naval games by the mid-1930s, notably with a new generation of precision tools, the dive-bombers, for which Japan was ready to be invested in intensive training. In 1940-41, as a result, pilots had an excellent training, probably among the world’s best, but to the massive cost of gasoline. We can see a trail there towards the events leading to Pearl Harbour.
This emerging concept of a mass pre-emptive aerial attack had the consequence of shifting the main battle fleet attention to battles over the horizon and naval games tactical and strategic plays showed this over time. Crucial to this, was the location of the enemy fleet before the reverse was true. It became vital to “outrange the enemy” in the air, and officers soon emphasized range in the new aircraft specifications, to the cost of protection, as superbly showed by the Zero.
IJN planes preparing to take off from Akagi before the attack on Pearl Harbour
The Kidō Butai: IJN’s master ace (1941)
Officially known as the 1st Air Fleet (第一航空艦隊, or Daiichi Kōkū Kantai it was known also as the Kidō Butai (“Mobile Force”). It was a logical development of what was said above, based at first on a single unit, by default the “1st carrier division” allowed by the commissioning of the Kaga and Akagi, added to the Hosho. They formed the backbone of the fleet until more modern carriers were admitted, four purpose-built ones and more conversions.
In December 1941, just when attacking Pearl Harbor, the 1st Air fleet was the world’s largest fleet of aircraft carriers, comprising three divisions (see later). However after Midway and other crippling battles for the IJN, the 1st fleet division became in 1944 largely a land-based fleet of “kichi kōkūtai” (base air unit(s)), its carriers played a bait role at Leyte.
The 1st air fleet was created in April 1941, the gradual gathering of three carrier divisions called tkōkū sentai (air flotillas) and a major component of the Combined Fleet (Rengō Kantai). A Second Kōkū Sentai (Sōryū, Hiryū) was added to the 23rd Kuchikutai (Destroyer Unit), and later a fourth Kōkū Sentai (Ryūjō), and more destroyers in August. A third Kōkū Sentai (3rd Carrier Division, with Zuihō, Hōshō was attached to First Fleet in December, at first distinct from First Air Fleet, but it was disbanded on 1 April 1942. A fourth comprised the IJN Ryūjō and Kasuga Maru (later Taiyō). A fifth Kōkū Sentai was added with IJN Shokaku and Zuikaku in December. The First Air Fleet was a naval battlegroup without any equivalent in the world at the time as no fleet concentrated as much carriers into a single force.
As coined by military historian Gordon Prange it was “a revolutionary and potentially formidable instrument of sea power.” and proved its worth by the fleet or concentrating enough air power to destroy the entire USN battlefleet in a couple of hours.
From its creation, this unit was under command of Vice Admiral Chūichi Nagumo, and chief of staff Rear Admiral Ryūnosuke Kusaka. Each “division” had two carriers, each with its own hikōtai (aircraft/aviation unit). Each kōkū sentai was a self-contained tactical unit, with or without destroyer escort, which can be detached or attached to others depending on the mission. As the area of operation stretched out fast, the 1st air fleet was thinned out. In New Britain and New Guinea in January 1942, only the 1st and 5th Kōkū Sentai participated in operations, the others operated separately. Of course, depending of the carriers themselves, these units had different capabilities. Light carriers such as Ryūjō and Kasuga Maru could only bring a dozen planes of each type for any operation. From 14 July 1942, the First Air Fleet was became two units, the Third Fleet and Eighth Fleet, while the 2nd and 5th Carrier Division were disbanded. As a carrier battle group, the Kidō Butai in December 1941 was the centerpiece of a massive “task force” comprising also an escort of two battleships, three cruisers, nine destroyers, supported by eight tankers, and a forward screening of 23 submarines, plus four midget submarines deployed for the initial failed harbor attack. This formidable unit was amputated of 2/3 of its potential at Midway and pretty much never recovered its strength for the rest of the war. In 1 July 1943, it was recreated Land-Based Air Fleet, on paper with 1,600 aircraft, but as completed it never reach this figure.
Japanese carrier-borne aviation
Japanese aviation was divided between the Army and Navy models, with a great deal of rivalry between the two, a bit like the USA. A code was soon created to differenciate between the two: Two letters and a number, coding the plane origin and purpose, a Japanese symbolic name, and on top the allied intelligence code, versus the factory designation for Japanese Army planes with the Type in Imperial years. For example, the N1K “Kyofu” (Rex), where N signified “floatplane fighter”, 1 as it was the first of the factory of this type, and K for “Kawanishi”. “Rex” was the allied intelligence code. A6M for example designated the sixth type of carrier fighter under this designation system, and that it was built by Mitsubishi. Zeke was the Japanese symbolic name and “Zero” the allied code, inspired by the Imperial year code Reisen (“year zero”). Note: Foreign planes built under licence are not included there.
Without contest, the A6M was the most famous IJN fighter in 1941. Agile, fast, with a long range and top-tier pilots, it brushed aside all opposition until late-1942 when the Hellcat and Lightning started to be introduced. Its army equivalent was the equally agile Nakajima Ki-43 “Oscar”.
–Mitsubishi 1MF (1921) 138 built, retired 1923
-Heinkel HD 23/Aichi Type H (1926) semi experimental fighter, 4 built
-Kawanishi K-11 (1927) experimental fighter, 2 built
–Nakajima A1N (1928), based on Gloster Gambet, 151 built, retired 1935
–Nakajima A2N (1929): 166 built, retired 1941
Note: The Navy also used the Gloster Sparrowhawk from 1931, 90 were in service.
–Mitsubishi A5M (1935), main fixed-train monoplane, 1094 built, retired 1945
–Nakajima A4N (1935) 221 built, until 1940, second line 1942.
–Mitsubishi A6M Zero “Zeke” (1939): By far the most famous navy fighter. 10,939 built in any variants
–Nakajima J1N Gekko (1941) “Irving” fast twin-engine heavy fighter, 479 built
–Kawanishi N1K-J Shiden “Georges” (1943) derived from the “Rex” floatplane fighter, circa 1400 built
–Mitsubishi J2M Raiden “Jack” (1942), 621 built
–Mitsubishi A7M Reppū (1944): Planned replacement of the legendary “Zeke”, codenamed “Sam”, 10 preserie built.
–Yokosuka MXY-8 Akigusa (1945), a clone of the German Me 163 Komet, which plans and parts arrived via U-Boat. About 50-60 were built but apparently never used.
The IJN also tested the Dewoitine D.510J in 1936, the Canadian Car & Foundry AXG1 in 1938, Heinkel A7He1 (12), Seversky A8V (20) the same year, the American Douglas HXD and Fairchild LXF1, and used 20 Seversky A8V recce monoplanes.
Navy land-based Torpedo Bombers
–Mitsubishi G3M (1935), 1,048 built, long range twin engine navy land-based bomber, codename “Nell”.
–Mitsubishi G4M (1939) “Betty”, Main long range twin engine torpedo bomber of the navy, 2,435 built
–Nakajima G5N Shinzan (1941) “liz” long-range quad-engine heavy bomber, 6 built
-The navy also experimented with the Mitsubishi Ki-67 bomber, with a torpedo-bomber, the “Yasukuni”, and a dedicated ASW plane, the Mitsubishi Q2M1 Taiyo.
–Nakajima B6N Tenzan (1941) coldename “Jill”, 1,268 built planned replacement for the “Nate”.
–Aichi B7A Ryusei “Jack” (1942), last IJN carrier-borne Torpedo bomber, 114 built
–Mitsubishi 1MT (1922), triplane 20 built retired 1928.
–Mitsubishi B1M (1923), 443 built, retired 1936.
–Mitsubishi B2M (1932) 206 built, based on Blackburn Ripon, retired 1939-1940
–Yokosuka B4Y (1935) 205 built, biplane, retired 1943
–Mitsubishi B5M (1936) fixed carriage monoplan bomber, 125 built
–Nakajima B5N (1937) 1,150 built, main torpedo bomber
–Yokosuka P1Y1 Ginga “Frances” (1943) Navy Land-Based twin engines Bomber, 1098 built
Mitsubishi MC-20-II, close to the L4M, Naval transport plane
–Yokosuka K2Y (1929), main navy trainer based on Avro 504, rarely mounted on floats. All 464 built were used by the Navy.
–Nakajima C2N (1930) staff carrier developed with Fokker, used by the navy and army (Ki-6), prod. unknown
–Mitsubishi K3M (1930), navy trainer and liaison, recce, 625 built, retired 1940s
–Mitsubishi 2MR (1932), carrier-based recce biplane, 159 built, retired 1937-38 as trainers
–Yokosuka K5Y (1934) 5,770 main IJN biplane trainer, with undercarriage or floats, used during WW2
–Hiro G2H (1933) 8 long-range recce/bomber land-based biplanes, most destroyed at Cheju Island in 1937
–Gasuden KR-2 (1934), light transport biplane, small prod.
-Nakajima C3N (1936) experimental recce monoplane with fixed undercarriage
-Nakajima L1N (1936) main transport monoplane twin engine, 351 built
–Mitsubishi L4M (1939) main twin-engine transport plane, 406 built
–Nakajima/Showa L2D (1939) large navy transport plane codenamed “Tabby”, DC-3 copy.
-In 1939 also first flew the Nakajima LXD-1, transport four-engined prototype.
-Kyushu K9W1 Momiji (1942) biplane trainer based on the Bücker Bu-131, 339 built
–Kyushu K11W1 Shiragiku (1942) monoplane advanced operations trainer, 798 built
–Nakajima C6N Saiun “Myrt” (1943) Navy Carrier Reconnaissance Plane, the fastest built by Japan, 463 built.
–Yokosuka MXY-7 Ohka (1944) codename “Baka” the famous suicide rocket plane, 852 built
Floatplanes & seaplanes
–Yokosho Rogou Kougata (1918), 218 built, retired 1928
–Yokosuka K1Y (1925) Main trainer/spotted floatplane of the Navy, 104 built, retired 1941
–Hiro H1H (1925) recce and ASW patrol seaplane, 60 built, retired 1938
-Aichi Type 15-Ko Mi-go (1925), semi-experimental seaplane, 4-5 built
–Yokosuka E1Y (1926): Main recce floatplane, 320 built, retired 1938
-Aichi Navy Type 2 (1928), experimental floatplane
–Nakajima E2N (1929): 80 built, retired in the late 1930s
–Yokosuka E6Y (1929), submarine-based recce floatplane, 10 built, retired 1943
–Yokosuka K4Y (1930), trainer/recce floatplane, 211 built, retired 1940s.
–Yokosuka E5Y (1930) 20 built, recce floatplane. Used by NOTORO, phased out late 1930s
–Aichi E3A (1930): Recce floatplane dev. with Heinkel, 20 built
–Nakajima E4N (1930), recce floatplane, 153 built, retired late 1930s
–Hiro H4H (1933) recce seaplane, 47 built, retired 1940
–Kawanishi E7K (1934) main recce floatplane, 533 built, served in WW2
–Nakajima E8N (1935) Main recce floatplane, 755 built, served WW2 codename “Pete”
-Kawanishi E10K (1934) experimental transport/recce floatplane
–Kawanishi H6K (1936) four engine flying boat, 215 built.
–Mitsubishi F1M (1936) 944 recce, last biplane floatplanes in the IJN
–Yokosuka H5Y (1936) Type 99 Flying Boat Model 11, 20 built
-Watanabe K6W (1937) experimental florplane trainder/recce
–Aichi E11A (1937) 17 gunnery spotting seaplanes (E11A Type 98)
-Kawanishi E11K (1937), two transport flying boats
-Nakajima E12N (1938), 2 recce floatplanes
-Nippi K8Ni1 (1938), 2 trainer floatplanes
–Watanabe E9W (1938) 35 shipboard recce biplanes
-Watanabe K8W (1938) 3 built, recce seaplane trainers
–Aichi E13A (1938) main recce monoplane floatplane, 1,418 built
-Kawanishi E13K (1938) 2 built, 3-seat shipboard recce.
-Kawanishi K6K (1938) seaplane trainer, 3 built
-Kawanishi K8K (1938), same, 15 built
-Nippi K8Ni1 (1938), same, prototype
-Nakajima E12N (1938), recce floatplane, 2 built
–Aichi H9A (1940), recce seaplane, 31 built
–Nakajima E14Y (1939), shipboard recce floatplane, 126 built
–Kawanishi E15K Shiun (1941) codename “Norm”, 15 built, floatplane Torpedo bomber
–Kawanishi H8K (1941) codename “Emily”, main long-range aquad-engine, 167 built
–Kawanishi N1K1 Kyofu (1942) “Rex”, main IJN floatplane fighter, variant, land-based fighter Kawanishi N1K-J Shiden- 1,532 built.
–Aichi M6A1 Seiran (1943) Navy Special Strike Submarine Bomber developed for the I-400 submarines, 28 built.
-Also was tested a flotplane trainer, the Aichi M6A1-K Nanzan Navy Special Strike Submarine Bomber trainer (1943, 2 built) and the Kyushu Q1W1-K Tokai-Ren, a twin-engine the same year codenamed “Lorna”.
Author’s illustration of the H8K “Emily”
About IJN seaplane carriers
IJN Akitsushima showing her amazing camouflage in April 1942. Technically she was a seaplane tender, so not a “carrier”, therefore these auxiliaries will not be covered here. The only seaplane she carried was provisionally stored in the workshops for repairs. Her sister-ship Chihaya was never completed and three more were cancelled.
IJN Notoro was the lead ship of a class of fleet oilers, also comprising IJN Shiretoko, Erimo, Sata, Tsurumi, Shiriya, Iro. They were part of the large 6-6-3 programme, laid down in 1919-21, they wer all sunk in WW2 except Notoro, converted in 1934 as a seaplane tender/carrier.
This 15,400 long tons, 140 tonnes ship was armed with 2 × 120 mm (4.7 in) L/45 naval guns and 2 × 76.2 mm (3 in) L/40 AA guns, and carried in 1924 already 8 Type 14-1 Yokosuka E1Y1 three-seat reconnaissance floatplanes. She participated from 1932 to the war in China, with E1Y3 floatplanes. In 1937 she deployed six Type 95 Kawanishi E8N2 “Dave” two-seat float reconnaissance biplanes, and received the same year two 80-mm (3.15-inch) guns and about twenty 20-mm AA guns. In 1938 she operated 6 Type 95 floatplanes, and in November 1941 she was about to be reconverted as an oiler. She was damaged near Java in 1943 and towed for repairs in Singapore, scuttled and BU in 1947.
IJN Kamoi carried 22 Nakajima E4N or 12 Yokosuka E5Y.
Kamoi was completed 12 September 1922 as a “special service ship”, fleet Oiler. From 27 September she made 25 missions from the Homeland and back with the fleet. In 1932, she was converted to seaplane tender at Uraga Dock, completed by February 1933 and re-assigned to the Combined Fleet as a seaplane tender. From June 1936, she joined the Third Carrier Division, and in 1939, overhauled, with flying boat tending facilities. By November 1940, she was assigned to the 24th Air Flotilla, 4th Fleet from December 1941.
In January 1942, she she covered the Rabaul and Kavieng invasions and from April 1942, 11th Air Fleet. In April 1943, she joined the 3rd Southern Expeditionary Fleet, Southwest Area Fleet. In January 1944, she was torpedoed by USS Bowfin off Makassar. Repaired in Singapore, she was converted back as a fleet oiler in April-August 1944. She was attacked by TF38 planes off Coron Bay and later from another Submarine. She was repaired in Yokosuka and joined the Hi-87 convoy to Singapore, but in January 1945, she was heavily damaged in Hong Kong. From 5 April 1945, still unrepaired, she was damaged so badly she sank sinking in shallow water.
Displacement: 17,000 tons (standard)
Dimensions: 149 x 20.4 x 8.4 (488 x 67 x 28 ft)
Propulsion: 2 shafts GE/Curtis turbine + GE electrical generators, 4 Babcock & Wilcox mixed-fired boilers, 8,000 bhp
Speed: 15 knots (28 km/h)
Armament: 2 × 140 mm (5.5 in), 2 × 76.2 mm (3.00 in), 2 × 76.2 mm (3.00 in) AA guns
Aircraft: 22 Nakajima E4N or 12 Yokosuka E5Y
Chitose class (1936)
Japanese seaplane carrier/tender Chiyoda in 1938, full speed.
A class of two seaplane tenders converted later to light aircraft carriers. The Washington Naval Treaty allowed Japan a certain tonnage by class to the IJN, and the Chitose-class were seaplane tenders, but designed for their quick conversion to aircraft carriers from the start, knowing in case of war, these limits would be gone. As seaplane tenders they srved nevertheless during the second sino-Japanese war and the early Pacific War and naturally were converted after the Battle of Midway at Sasebo Naval Yard. They were out in January 1944, and participated in the Battle of the Philippine Sea. Both were sunk in the Battle of Leyte Gulf. Conversons work implied the fitting of a single hangar, aigmented by an additional 6 feet 7 inches, and a full flight deck serviced by two lifts (see later).
IJN Mizuho in 1939
IJN Mizuho was a near sister to the Chitose, but dropping turbines for less powerful diesels, whereas gaining extra range. 24 seaplanes was her capacity, but her deck was also tailored to carry and drop twelve midget submarines in alternative missions. She was used as an auxiliary ships for invasions support, starting with the Fourth Surprise Attack Force. By March 1942, with Chitose her planes damaged USS Pope, and the destroyer was latter reported to Ryūjō and Ashigara and Myōkō which finished her off. Her career ended when USS Drum torpedoed IJN Mizuho on 1st May 1942, 40 nautical miles off Omaezaki, Japan just before midnight. She sank four hours later, on 2 May 1942, carrying 101 lives with her for 472 survivors.
Built at Kure Naval Arsenal (1938-1942), IJN Nisshin had 2 aircraft catapults and reworked launching, lifting, carrying and operating facilities for 12 floatplanes alternative to 12 Type ‘A’ midget submarines. She profited from the no(tonnage cap in the Washington Naval Treaty and London Naval Treaty for seaplane tenders, but was not designed for easy coversion as a carrier in wartime. She was loosely derived from the Chitose-class, ordered under the 3rd Naval Armaments Supplement Programme of 1937. She could carry 900 tonnes of aviation fuel and operated in wartime 12 Kawanishi E7K Type 94 “Alf” and/or Nakajima E8N Type 95 “Dave”, plus Mitsubishi F1M floatplanes, stored on the deck as there was no hangar.
She was armed by six 14 cm/50 3rd Year Type naval guns in three turrets and 24 Type 96 25 mm AA guns in eight triple mounts and the modification to carry 12 Type A Kō-hyōteki-class submarines, was paid by having only twelve aircraft alongside. She was more powerful at 47,000 bhp, with 2-shaft geared steam turbines for 28 knots and a range of 11,000 nautical miles, so she was often requested to perform high speed transport missions, carrying the most vital assets in isolated places.
Her completion was delayed by design changes until 27 February 1942 and in March she joined Vice Admiral Teruhisa Komatsu’s IJN 6th Fleet with Chiyoda and Aikoku Maru for exercizes. At the battle of Midway, IJN Nisshin carried twelve Type A Kō-hyōteki-class midget submarines, for Kure Atoll, to be used as a seaplane base to target Midway. The operation was cancelled and she returned to Hashirajima. In September 1942 she was at Kavieng (Solomon) and conducted many Tokyo Express transport runs to Guadalcanal. Later that mmonth she was near-missed by USS Sculpin east of Kokoda. She received air bomb damage north of Tassafaronga in October (Battle of Cape Esperance) and was sent in November to Truk, used in 1943 as fast transport between Japan, and Truk-Rabaul. In June 1943 she was sent to New Guinea, carrying reinforcements to Bougainville Island. On 22 July her convoy was attacked at 40 nautical miles southwest of Buin by three waves of American bombers (SBD Dauntless, Consolidated B-24 Liberator). IJN Nisshin evaded B-24s bombs, hard-turning at 34 knots, but she would receive four 500-pound (230 kg) and two 1,000-pound (450 kg) bombs for the Dauntlesses in other strikes. Her aviation fuel stores were blasted, and she capsized and sank just 15 minutes after air raid started, with only 178 surviving. The 900 troops and most of the crew went down with her.
The case of Akistu Maru
This ship was nothing short as the world’s first modern assault ship. Indeed, she was not only at the same time a Japanese landing craft depot ship, and escort aircraft carrier and a autogyro carrier, so an ancestor of modern helicopter carriers.
Akitsu Maru was a passenger liner taken over before completion by the Imperial Japanese Army, fitted with a flight deck but no hangar to simplify construction. Instead planes were stored below the flight deck, on the main deck. Conventional aircraft could fly off from her deck but not land, until July 1944 when a KX arresting gear was fitted. The Kokusai Ki-76 (a recce plane close to the Fieseler Storch) and Kayaba Ka-1 were flown off Akitsu Maru. The Ki-76 had so much sustentation that she actually could land on her short deck. The Kayaba Ka-1 was an autogyro, so landing and taking off in short distances. The ships also could also carry 27 Daihatsu-class landing craft. The presence of both troops and vehicles with landing crafts in a flooded dock below and aviation support above, made the ship the world’s first amphibious assault vessel, an early LHD.
Her role was to provide an air cover during amphibious and landing operations but she became an aircraft ferry, until 18 November 1943 when she was sailing with the torpedo boat Tomozuru, off the entrance to Manila. She was ambushed by the submarine USS Crevalle, which torpedoed her, and incorrectly reported her sunk. In fact she survived, was repaired and resumed her service, until sank for good by USS Queenfish on 15 November 1944. On board, all 2,046 men, of the crew and IJA’s 64th Infantry Regiment went with her. Her sister ship Nigitsu Maru was sunk by USS Hake on 12 January 1944. She was not alone, part of a secret plan of the IJN to built a fleet of Landing craft carrier.
The Prototype Shinshū Maru (photo) completed in 1935 was converted with a floodable well dock the next year. She was the world’s first dkc landng ship, able to rapidly launch landing craft with stern and side gates. In total with rotations, she could land 2,200 soldiers way faster than any assault ship, with men climbing onboard crafts. She took part in the invasions of Shanghai, Malaya and Java. More will be told on a dedicated IJN amphibious ships/crafts page.
From this proof of concept, the IJN staff devised the Hei-type landing craft carriers: Apart Akistu Maru, her sister ship Nigitsu Maru was completed in March 1943. Two others were based on Hitachi’s 8,000-ton, 19 knots (22 mph; 35 km/h) Type-M cargo. As modified as the Type-MB they could carry twelve Toku-Daihatsu class landing craft, launched via stern doors, horizontal funnels on starboard and flight deck. IJN Kumano Maru was completed in March 1945 but saw little service, as repatriation ship after the war, and Tokitsu Maru was still incomplete, and was rebuilt after the war as a whaling ship.
Displacement: 11,800 tons (standard)
Dimensions: 143.74 x 20 x 7.84 (471 x 64 x 26 ft)
Propulsion: 4 boilers, 2 geared turbines 7,500 shp (5,600 kW)
Speed: 20 knots (37 km/h)
Armament: 2 × Type 88 75 mm, 10 × 1 Type 38 75 mm, 6x Type 25 mm Type 96 AA
Aircraft: 8 autogyros, up to 30 as aircraft ferry.
Japanese Aircraft Carriers (IJN) video 日本の航空母艦
Military History visualized – about the Kido Butai
IJN Soryu’s island, colorized by Irootoko Jr.
Conway’s all the world’s fighting ships 1922-47
Kido Butai in the Indian Ocean – 1942 Part I
Nomenclature of IJN Carriers
Hosho was the first Japanese aircraft carrier. She was originally laid down as the large oil tanker Hiryu, whose construction began in 1919, but the Japanese high command aware of the success of the British in the field of aircraft carriers requisitioned this ship in 1920 for converion. The British sent assistance with the Semphill technical mission, to preside over this design work.
In 1921, she was was launched and put into service in 1922, earlier than HMS Furious. At that time, the Japanese naval aviation became an independent body of the army.
The Hosho was rather fast, enough to follow the squadron, and her modest dimensions remained exploitable by the small planes of the time. She had a small command bridge and a tripod mast, removed in 1923 to achieve a “flush-deck”, kept since. She had six small funnels extending to port and starboard, which can be raised or lowered depending on the use of the deck. She had no catapult, while her narrow deck served as a runway for only a few planes, stored in the hangar below. In 1941, considerd obsolete, Hosho was no longer part of the squadron, she was relegated to secondary duties as training ship since 1941, and aicraft transport. In 1944, her flight deck was lengthened, reaching the full length of the hull, and the armament was increased to 8 more 25 mm AA, with only 11 aircraft on board. She operated in homs islands and served as a repatriation vessel for prisoners and Japanese garrisons isolated from the Pacific in 1946-47, before being delivered to the scrapyard.
IJN Hosho in 1937
Displacement: 2,500 t. standard -10 100 t. Full Load
Dimensions: 176 m long, 18 m wide, 6.2 m draft
Machinery: 2 shafts turbines, 12 boilers, 30,000 hp.
Top speed: 25 knots
Armament: 4 x 140 mm, 8 x 25 mm AA, 2 x 7.7 mmn AA, 21 aircraft
IJN Akagi in 1927 and 1941
The Amagi and Akagi were two battle cruisers of the class of the same name, ordered in 1917 and whose construction was well completed when the Washington Treaty came into effect in 1921. Both had been launched and the completion work was going on. good train. The Admiralty decided to turn them into aircraft carriers to avoid demolishing them. In 1923, however, at the beginning of these reconversion studies, a trench of land ruined the construction basin where the Amagi was located, and at the same time its hull, good this time for the demolition. It was decided to fall back on the Kaga, also from an unfinished ship. The Akagi was taken over for reconstruction between 1923 and 1927. It was launched in 1925. At that time, it was almost as big as the Lexington Americans, but with a speed of two knots. It was at its launch anyway much larger and of more valuable military value than the Hosho.
The first version of the Akagi, in 1927, was unusual because the buildings had two runways at the front, and a landing lane at the stern, with no island or apparent gangway, and with two double turrets. pieces of 203 mm, the rest being in barbettes. This weapon worthy of a heavy cruiser dates back to a time when the concept of aircraft carrier was not yet fully understood and where it was envisaged that these vessels could be relatively versatile and able to defend themselves. True specialization will come when the effectiveness of the apparatus alone will be sufficient to render all this surface artillery obsolete.
In 1935-38, he was taken to the basin for a redesign, modeled on the Kaga model, and through which he received a single integral track, a bridge of command, a new truncated chimney on the side, imposing lateral ballasts. , and a shed expanded and refitted. A hangar was added to it, but its turrets were removed, keeping only the 203 mm pieces in barbettes at the stern. At the same time he received new, more powerful machines, his speed gaining two tenths of a knot. Her tonnage had risen from 33,820 to 40,650 tons. The hangar was much larger, draft and its width larger but length unchanged. Her onboard staff amounted to 91 aircraft. In operations however, 72 aircraft were actually operational. Although faster than Kaga, she had a much lower armor.
Akagi in 1928
IJN Akagi in 1941, top and profile
Displacement: 46,500 t. standard – 42,750 t. Full Load
Dimensions: 260.7 m long, 31.5 m wide, 8.7 m draft (full load)
Propulsion: 4 propellers, 4 steam turbines, 19 Kampon boilers, 133,000 hp, Maximum speed 31.2 knots
Armor: Maximum (belt) 250 mm, bridges 50 mm, stores with ammunition 100 mm.
Armament: 6 x 203 mm (6×1), 12 x 100 mm (12×1), 28 x 25 mm AA (14×2), 91 aircraft (miscellaneous)
Crew: 2050 (NEW)
IJN Kaga 1928
Kaga was the third Japanese aircraft carrier. Like Akagi from the reconstruction of a canceled ship project due to the moratorium of the Washington Treaty. In the case of Kaga, it was the class Tosa battleships. As a result, it was a shorter and slower building than the Akagi, but with better protection of the internal bridges.
It was not planned to transform it at first, because it is the twin of the Akagi, of the Amagi class, much more advanced in its construction (launched, in completion), which was preferred in order to simplify the studies conversion and for the homogeneity of the fleet, like the American Saratoga class at the same time. but a violent earthquake caused the destruction of the basin in which was this twin of the Akagi, whose hull was dislocated.
The Kaga was converted from 1923, the ship was started in Kure in 1920 and launched in 1921. This long work ended in March 1928. At that time, the ship was presented in a very different aspect from that which it will be known in 1941: it had a landing deck only at the rear, the front being reserved for two superimposed tracks of takeoff. Its chimney was starboard, and the huge duct ran along the entire length of the track to the rear, a configuration that will not be retained later. It also had two 203 mm double turrets at the front and six barbettes.
It did not have a gangway, but a kind of telescopic cabin at the end of the runway, as well as another bridge located at the bow below the landing deck. In this configuration, there were also 12 120 mm pieces in double turrets and 22 heavy machine guns. It was loaded with 60 aircraft, and measured 238 meters long and 29.60 wide with 7.9 meters of draft and 33,160 tons tested. His machines developed 91,000 hp, giving it a speed of 27.5 knots.
In 1934-35, he was taken to the basin for a new overhaul, where he received a single integral track, a bridge of command, a new chimney truncated on the side, imposing lateral ballasts, and a shed enlarged and refitted. A hangar was added to it, but its turrets were removed and the 203-mm pieces were rearranged into barbettes at the rear. At the same time, he received new, more powerful machines, his speed gaining a knot. Its dimensions increased considerably (see sheet), which allowed to increase its embarked staff to 90 aircraft. In operations however, 81 planes were really usable, and on the eve of Midway, 66.
Kaga formed the Akagi backbone of the Japanese Navy aircraft carrier force and was part of the fleet that attacked Pearl Harbor on December 7, 1941. His aircraft made two assaults before Admiral Yamamoto decided to cancel the third, believing that the surprise effect no longer played in their favor. He was also present at the Battle of Midway, but tactical errors and bad luck made it a success, despite an objective chance of winning.
When the third wave of Japanese aircraft was ready to take off, loaded with gasoline, bombs and torpedoes, both on the crowded deck and in the hangars, the Douglas SBD Dauntless and Vought Vindicator of USS Yorktown, Hornet and Enterprise (131 aircraft in total) are based on the four Japanese aircraft carriers and try to sink them. Cleverly maneuvered and covered by the hunt, counting on their own DCA, they repel the assault. Their devices will go to Yorktown. But an hour later, at 10:20, the remaining American aircraft come back in force and their bombs are a carnage. The Kaga, hit by 4 projectiles, is immediately ravaged by fires, which explode in explosion to the fuel tanks, causing the complete destruction of the ship. He capsized and sank the next day, his crew having delayed the inevitable for more than 33 hours.
Kaga in 1928
Kaga in 1941
Displacement: 38,200 t. standard -43 650 t. Full Load
Dimensions: 247.65 m long, 32.5 m wide, 9.5 m draft
Machines: 4 propellers, 4 turbines, 8 boilers, 127,000 hp.
Top speed: 28.3 knots
Armor: Decks 265, belt 250
Armament: 10 x 203, 16 x 100, 30 x 25 mm AA, 90 aircraft
This light Carrier was part of the Japanese Navy in 1941, in the Kido Butai. It came from a request from the 1927 naval program that demanded a new, more economical model. Built from a “cruiser” hull, long and relatively narrow, but to maximize the capacity of aircraft, she received a double hangar and a considerable armament for her size, making her higher than usual. The result was not long in coming: Launched in April 1931 and completed in May 1933, IJN Ruyjo was dangerously unstable, taking an uncontrollable roll as she was overloaded with high metacentric point. In heavy seas this made any deck landing impossible. In addition, her prow, too low, plowed heavily and the bridge became a breakwater, denying the crew any visibility in between waves.
In the face of this failure, IJN Ryujo was taken over for a radical reconstruction in 1934-36. The hull structure was reinforced, ballasts were added, and the armament was reduced from six twin 5-in/127 mm to eight. The bow was raised by a level in 1940. The AA was increased in 1936 with four 25 mm AA, then 22 in 1942 plus twenty four 13.2 mm. IJN Ruyjo was very active, although not part of the kido Butai, she was sent to the East Solomon Islands and there was hit by US naval air force, taking four bomb hits and a torpedo. She sank on August 24, 1942.
IJN Ryujo in 1941
Displacement: 10,600 t. standard -13 450 t. Full Load
Dimensions: 179.90 m long, 20.80 m wide, 7.08 m draft
Machinery: 2 steam turbines, 6 boilers, 65,000 hp.
Top speed: 29 knots
Armament: 8 x 127 AA, 4 x 25 mm AA, 48 aircraft
IJN Soryu was the first aircraft carrier designed as such from the outset since the Hosho of 1921, ordered under the 1931-32 plan. Built in Kure, she was laid down in November 1934, launched in December 1935 and completed in December 1937. Although larger than the latter, following the evolution of modern aircraft, she had two hangar decks served by three lifts. She was very fast, well enough to escape capital ships, built and armed to withstand attacks of light ships such as destroyers, not to mention the rampart constituted by her major air group, 71 aircraft in all, much more than the Hosho. She served as a model for the following carriers.
IJN Soryu took part in the campaign in China when it entered service, and then went on squadrons exercises until December 1941, when her group was sent to Pearl Harbor with the Kido Butai (2nd division). She then participated in June 1942 in the Battle of Midway. Hher fighters made a carnage among American torpedo bombers, but as her air group was converted from an attack on Midway tp an attack on the USN carriers, planes loaded with bombs and fuels cluttering her deck and hangars, Douglas Dauntless dive bombers hit her after Kaga and Akagi. She took
three bombs hits while her hull was damaged by several near-hits. Fuel tanks were dislocated, massed planes exploded in chain, fire spread to the two hangars causing a series of new explosions. A few minutes after this attack, Soryu was no more than a huge fire and sank at the end of the day, as most survivors evacuated.
IJN Soryu in 1941
Displacement: 15,900 t. standard -18 500 t. Full Load
Dimensions: 222.00 m long, 21.30 m wide, 7.62 m draft
Machinery: 4 steam turbines, 8 boilers, 152,000 hp.
Top speed: 34.5 knots
Armament: 12 x 127 AA, 28 x 25 mm AA, 71 aircraft
IJN Hiryu in 1939 and 1941 – Colorized by irootoko jr.
Coming from the 1931-32 program including Soryu, IJN Hiryu was laid down two years later and closely inspired by it. She was the same size and tonnage, took most of her features, but was extended one meter to carry extra fuel and fuel oil. In addition, internal protections were reinforced and the bow raised from a level to ensure better seakeeping. Her island bridge was instead reported to the center of the ship, starboard. Finally her AA was increased by three 25 mm AA and she carried 2 more planes.
IJN Hiryu was launched in November 1937 and completed in July 1939. She was operational at the outbreak of the war but her operational life was relatively short: Part of the Kido Butao in December 1941 with Soryu, she also took part in Japanese landings and the great Pacific offensive, in Yamamoto’s squadron at the time for Operation “Mi”. Seizing the island of Midway, was a vital step, an atoll having an obvious strategic position in the Pacific, a milestone between the US and Japanese coast and an US air base and transit base for Pan American airways.
In this momentous operation, Hiryu teamed with Nagumo’s (reduced) Kido Butai with Kaga, Akagi and Soryu. At 10:24, after her Zero fighters repelled several attacks, and just at the moment when the first aircraft of the counteroffensive took off, a squadron of dive bomber arrived. Hiryu was catch with her bridge and hangars loaded with bombs and aviation gasoline in the inter-deck, but she was lucky to be far enough away from the other three at this time to be spared. After the American attack annihilates the three aircraft carriers, iryu managed to get off without damage.
These save the honor of the combined fleet as her air group managed to destroy USS Yorktown, the only major American loss of the battle. The first attack took place at 10:40, the second at 12:45. Rear-Admiral Yamaguchi, onboard the ship, thought two large American aircraft carriers have been destroyed. But Yorktown was not sinking until 5 days later, after being evacuated, torpedoed by a submarine.
IJN Hiryu will pay for this, around 5 pm, when a wave of Navy aircraft from USS Hornet and Yorktown, which Yamaguchi thought was out of action, hit Hiryu bad. The latter survived, only to be spotted and destroyed by American destroyers the next day with torpedoes. With the loss of Hiryu and the three others, experienced pilots and trained crews, Japan was left without any possibility of destroying what was left of the Pacific fleet in a short time.
Displacement: 17,300 t. standard -21 900 t. Full Load
Dimensions: 227.40 m long, 22.32 m wide, 7.84 m draft
Machines: 4 steam turbines, 8 boilers, 153,000 hp.
Top speed: 34.3 knots
Armor: 90 mm Belt, 56-150 mm magazine decks, 25 mm engine decks
Armament: 12 x 127 AA, 31 x 25 mm AA, 73 aircraft
These two famous heavy aircraft carriers were approved in 1937 with the aim of constituting a considerable improvement of Hiryu and Soryu, considered out of date. Not only were they enlarged to increase the carrying capacity of aircraft, as fuel oil, but also to protect them more effectively. They adopted a double hangar, yet still relatively unprotected, only ammunition stores with armor plates ranging from 100 to 165 mm.
Shortly after Midway, both took advantage of their immobilization to pour concrete into existing spaces between bulkheads and fuel tanks. As a result, Shokaku which was launched in 1939 and completed in August 1941, and her twin Zuikaku in September, were both operational at the time of Operation Tora against Pearl Harbor.
They carried 84 planes, of which 72 were operational at all times, the others kept in reserve, which was a record for a Japanese carrier. A third unit was assigned to this class, following an error by the American intelligence services, IJN Ryukaku. She was actually confused with Shoho during the Battle of the Coral Sea.
Their AA was increased dramatically to 70 and then to 96 25 mm AA, plus 6 rocket launchers with 28 tubes each. Their operational career was quite rich, since after Pearl Harbor, these two ships were were engaged during the battle of the Coral Sea, Shokaku being badly damaged in May 1942, then again in October during the Battle of the Santa Cruz Islands, and ultimately torpedoed and sunk by USS Cavalla during the Battle of the Philippines on June 19, 1944.
Her twin Zuikaku participated in these same battles with no great damage but met her fate at the battle of Cape Engano, during the great operation of Leyte in October 1944 where she was hit by no less than 6 torpedoes and 7 bombs before sinking. At that time she had lost already lost of her air group, manned by novice pilots.
IJN Shokaku in 1941
Displacement: 25,675 t. standard -32 100 t. Full Load
Dimensions: 257,50 m long, 26 m wide, 8,87 m draft
Machinery: 4 steam turbines, 8 boilers, 160,000 hp.
Top speed: 34.2 knots
Armor: Belt 70, Stores 130-165, Machine Bridge 100 mm
Armament: 16 x 127 AA, 42 x 25 mm AA, 84 aircraft
These two aircraft carriers, Zuiho and Shoho, were started as fleet tankers, IJN Takasagi and Tsurugisaki. It was in this guise that both were pressed into service in 1939. Zuiho was quickly converted in 1941, on the model of the conversion of Takasagi, completed in 1940, while the ship was nearing completion when the decision of the conversion was taken. IJN Shoho, formerly Tsurugisaki, was accepted into service in January 1942.
Their economic diesels well adapted to their old function were replaced by destroyers geared steam turbines to follow the fleet. They had only one hangar and no tower bridge. Their flying deck was shorter than the hull. IJN Shoho participated as her sister-ship in the Battle of the Coral Sea in May 1942, and was the first IJN aircraft carrier to be sunk, hit by no less than 11 bombs and 7 torpedoes. IJN Zuiho saw her AA increased considerably, rising to 48 25 mm guns in 1943, then 68 in 1944, with 8 rocket launchers with 28 tubes each. She was present at the Battle of Leyte, sunk on 25 October at Cape Engano by the American Air Force.
IJN Zuiho in 1941
Displacement: 11,262 t. standard -14 200 t. Full Load
Dimensions: 204.8 m long, 18.2 m wide, 6.6 m draft
Machinery: 2 propellers, 2 turbines, 4 boilers, 52,000 hp.
Top speed: 28 knots
Armament: 8 guns 127, 8 guns 25 mm AA, 30 aircraft
This ship was originally the seaplane tender IJN Taigei, in service since 1935. In 1941, the need for new aircraft carriers meant that she was sent in drydock for conversion into an aircraft carrier. Her diesels were replaced by turbines. She was completed and tested in November 1942, but still too slow and rolling heavily, in addition to excessive vibrations that hindered the accuracy of AA. There was no tims for a reconstruction, so she was used as a training carrier. She was present in Kure in March 1945, bombed and severely hit but remained afloat and eventually sunk in 1946.
IJN Ryuho was a 1937 seaplane tender converted in 1942
Displacement: 13,360 t. standard -16 700 t. Full Load
Dimensions: 215.6 m long, 19.6 m wide, 6.6 m draft
Machinery: 2 propellers, 2 turbines, 4 boilers, 52,000 hp.
Top speed: 26 knots
Armour: Max: 9 mm
Armament: 8 x 127 mm cannons, 38 x 25 mm AA guns, 31 planes
The urgent need for new aircraft carriers even before the war meant that the Admiralty started to use civilian hulls. In this case, big and fast ships had preference. Kashiwara and Izumo Maru were requisitioned in 1940, and converted first into armed transports and then in drydock for conversion as carriers. Work was completed in 1942 and the ships were back into service two months apart. A new configuration for the boiler rooms was tested on them, and their bridge was moved aside to clear of the flying deck while tilting the funnel to the side, a configuration closer to what was done on Allied carriers which was highly successful.
These two ships, IJN Junyo and Taiyo, were large enough to carry 53 planes, but their low speed (25.5 knots) made them unsuitable for the Kido Butai. In addition they had two hangars and two lifts, but protection was insufficient, especially underwater while these hangar were quite low. They participated in several operations, and IJN Hiyo was finally sunk in June 1944 during the battle of the Philippine Sea by the single torpedo from a Grumman TBM Avenger. IJN Junyo, like his twin, saw the installation of forty 25mm AA guns in 1943, and in June 1944, 76. She was badly damaged twice but survived, was repaired and in 1945 she was in home waters, in Kure. Repaired, she was able after armistice, to repatriate Japanese POWs and troops and was BU in 1947.
IJN Junyo in 1942
Displacement: 24,140 t. standard -28 300 t. Full Load
Dimensions: 219.3 m long, 26.7 m wide, 8.15 m draft
Machinery: 2 propellers, 6 boilers, 56 250 hp.
Top speed: 25.5 knots
Armor: 10 mm oil tanks
Armament: 12 guns 127, 40 guns 25 mm AA, 53 aircraft
The 1939 plan had approved the construction of a new heavy-duty fleet aircraft carrier of the improved Shokaku type. Plans were reworked many times, and the laying of the Taiho keel took place in Kawasaki on July 10, 1941. These plans incorporated several innovative aspects, such as the fully armored deck, a feature desired in the light of events in the Mediterranean, especially the amazing survival of HMS Illustrious before Italo-German aviation.
IJN Taiho also lacked a bridge, at the expense of carrying capacity but this benefitted stability, considered insufficient for the Shokaku and his twin. On the other hand, the hull was considerably longer and wider, and in the end, this ship proved to be able to contain a fleet of 84 aircraft (of which 53 were actually operational at all time), same as Shokaku.
Her AA was revised upwards, with fifty-one 25 mm AA at the start. The other novelty was a larger offset bridge and an integrated tilted funnel, echoing what was done among the allies. Her 100 mm dual-purpose turrets were the new model placed on Akizuki super-destroyers. Taiho was also fast, albeit a little less than her predecessors, but had superior autonomy. She inaugurated a new ambitious series of ships, two others planned for the 1942 plan (No. 801 and 802), and another five to the 1942 addendum plan. None was started.
IJn Taiho was launched in April 1943, completed in March 1944, but had a very short operational career since her first major operation was the Battle of the Philippine Sea during which she unsuccessfully used her air group but was torpedoed by USS Archerfish on June 19, 1944. The initial explosion broke aviation fuel lines, leading to extremely flammable vapors invading the entire hangar, all degenerating into a series of devastating explosions. She sank, literally torn to pieces, and there were virtually no survivors.
IJN Taiho in 1944
Displacement: 29,300 t. standard -37,720 t. Full Load
Dimensions: 260 m long, 27.70 m wide, 9.59 m draft
Machinery: 4 steam turbines, 8 boilers, 160,000 hp.
Top speed: 33 knots
Armor: Belt 56, flight deck 80, internal partitions 130, stores 151 mm
Armament: 12 x 100 AA, 51 x 25 mm AA, 84 aircraft
IJN Chitose in 1941
IJN Chitose in 1944
In 1941, the Japanese Imperial Navy also had six large aviation transports, armed as cruisers. The Chitose class in 1936 was one of those. These were the last and largest vessels of this type. These floatplane transports were operational units capable of operating observation and combat aircraft squadrons to cover the fleet. IJN Chitose was launched in 1936, Chiyoda in 1937, and Mizuho, a little different, in 1938. These were large vessels capable of operating 24 aircraft, and capable of 29 knots for the first two and 22 for Mizuho. The latter differed by her machinery, less powerful. IJN Chitose and Chiyoda were converted in 1941 for the transport of attack submersibles, their stern being lowered and provided with a ramp. They only carried 12 planes, but also 12 type A submersibles.
They also differed in armament IJN Mizuho having three 127 mm twin turrets, while the first two had two turrets. IJN Chitose and Chiyoda were requisitioned after Midway’s losses to be converted into aircraft carriers. After completion, Mizuho became the last of her class still serving in her initial role. Her slow speed prevented converted. She was also designed to carry 12 mini type A attack submarines. IJN Mizuho was sunk by an American submarine on 2 March 1942. Both Chitose and Chiyoda were sunk at the battle of Cape Engano on 25 October 1944.
Displacement: 10,929 t. standard -11,960 t. Full Load
Dimensions: 183.6 m long, 18.8 m wide, 7 m draft
Machinery: 2 propellers, 2 diesels, 15 200 hp.
Top speed: 22 knots
Armament: 6 x 127 mm (2 × 3) guns, 12 x 25 mm AA guns, 24 seaplanes
IJN Shinano in Tokyo Bay
The conversion of the most powerful warship of all time into an aircraft carrier would give the largest and best armoured aircraft carrier of the Second World War. IJN Shinano, with her 72,000 tons at full load even exceeded USS Midway launched in 1945, despite Midway was longer than 24 meters. The latter displaced “only” 59,000 tons fully loaded. The third unit of the Yamato class saw her construction suspended in December 1941. In June 1942, Midway’s losses prompted the high command to convert her into an aircraft carrier. Work started at that time and Shinano was launched in October 1944 and completed a month later, a real tour de force.
Her single main hangar was served by two lifts, and was heavily armored. The hangar deck itself was the initial armored deck of the battleship, bomb-proof as it retained its entire initial armor thickness. Total carrying capacity was “only” 100 aircraft, of which 70 were usable, the others kept in reserve, and only 47 actually operational at all time for the air group. IJN Shinano’s AA peaked with 145 25-mm guns and 12 rocket launchers. This wall of fire was in principle impassable, but exactly 10 days after her commissioning, her crew still testing all systems, she was spotted and torpedoed during her first and only shakedown trip off the Japanese coast by the submarine USS Archerfish, launching a full salvo. Her good underwater protection however prevented the ship from capsizing, and she stayed afloat for 7 hours, leaving pkenty of time to evacuate her crew and try to save her, and later evacuate her when she sank on November 29, 1944.
IJN Shinano in 1945
Displacement: 62,000 t. standard -71 890 t. Full Load
Dimensions: 266 m long, 36.3 m wide, 10.3 m draft
Machinery: 4 propellers, 4 turbines, 12 boilers, 150,000 hp.
Top speed: 27 knots
Armour: Belt 208, flight deck 80, hangar deck 180
Armament: 16 guns 127, 145 guns 25 mm AA, 12 LR (28 R), 47 aircraft
These large aircraft carriers were ordered in 1941 as part of the mobilization plan. To save time, they were based on the Hiryu, and differed by some minor details such as the bridge or the two lifts. Six keels were laid down at Yokosuka, Mitsubishi, Kawasaki and Kure. The class should consist of Unryu, Amagi, Katsuragi, Kasagi, Aso and Ikoma.
The first three were started in 1942, launched in 1943 and completed in 1944, Unryu and Amagi in August, and Katsuragi in October. A seventh was ordered, but never started, and another 10 planned in the 1943 plan. They differed somewhat in tonnage and Amagi and Katsuragi received no less than eight nine 25mm guns instead of fifty-one on Unryu.
Only these three vessels had an operational life, however short. At the time, they were no experience pilots to gave them and aviaton fasoline was already in shot supply. None will participate in the battle of Leyte, or a major battle. Their main purpose was to serve as platforms for Kamikazes attacks, trying to delay the inevitable fall of Iwo Jima and Okinawa. Fuel reserves were counted as well.
IJN Unryu was torpedoed by the submarine USS Redfish in the China Sea, IJN Amagi was bombed Kure by the US 3rd Fleet, just like Katsuragi and the other three being completed. IJN Katuragi was later refloated and used as a transport to repatriate Japanese prisoners and evacuate small isolated garrisons of the Pacific, well into 1946. IJN Katsuragi was scrapped in 1947.
IJN Unryu in 1945
Displacement: 17,200 t. standard -22 400 t. Full Load
Dimensions: 227.4 m long, 22 m wide, 7.8 m draft
Machinery: 4 propellers, 4 turbines, 8 boilers, 152,000 hp.
Top speed: 34 knots
Armor: Max 150 mm (ammo stores)
Armament: 12 x 127, 51 x 25 mm AA, 65 aircraft
IJN Taiyo in 1945
The rather extraordinary losses suffered by Japan because of US submersibles forced the admiralty to apply recipes of their enemies to face the same danger, and recommended solutions included the use of cheap escorts vessels, submarine hunters, and escort aircraft carriers. Therefore in late 1941, the Admiralty requisitioned the steamer Kasuga Maru then in completion to Mitsubishi, and she was transferred to Sasebo Naval yad for reconstruction.
She was soon equipped with a hangar, AA and specific equipment, back into service under the name of Taiyo with her original machinery. IJN Nitta Maru and Yawata Maru being of the same type, it was decided to requisition them in turn, and to transform them the same way, giving a class of three ships. They were commissioned in May 1942 (Unyo) and November 1942 (Chuyo). But the Japanese were not used to this type of aircraft carrier, and they were used as transport aircraft able to defend themselves with their own aircraft, and for training pilots.
Their AA varied during their service, between six and eight 127 mm and six 120 mm for Taiyo, with initially eight 25 mm, then 24 on Taiyo and Unyo, and 22 plus 5 heavy 13 mm machine guns for IJN Chuyo in 1943. In 1944 Taiyo and Unyo yielded two of their 127 mm turrets for 265 mm tubes batteries, for a total of 68, as well as ten 13 mm heavy machine guns. But the danger came again, not from the sea, but American submersibles. IJN Taiyo was torpedoed by USS Rasher in August 1944, and Unyo by USS Barb in September 1944. Chuyo was previously sunk by USS Sailfish in November 1943.
Displacement: 17,830 t. standard -19 700 t. Full Load
Dimensions: 180.2 m long, 22.5 m wide, 7.8 m draft
Machinery: 2 propellers, 2 turbines, 4 boilers, 25,200 hp.
Top speed: 21 knots
Armor: 150 mm (stores)
Armament: 4 guns of 127, 68 guns of 25 and 10 mitt. 13.2 mm AA, 27 aircraft
IJN Kaiyo in 1945
This escort carrier was the former liner SS Argentina Maru, launched in 1938. She served first as troop transport until December 1942 and like her twin Brazil maru sank in 1942, was chosen to be converted into an aircraft carrier. Work ended in November 1943, when IJN Kaiyo was completed. In this new configuration she saw her diesels replaced by for destroyers’ turbines, and served both as an aircraft carrier and training ships for pilots. In 1944, their AA was increased to forty-four 25 mm AA, and 6 rocket launchers with 28 tubes, with also eight ASW grenades attached to side cradles. IJN Kaiyo remained in home waters in 1945 and in August she was bombed by US Navy aircraft, BU in 1947.
Displacement: 13,600 t. standard -16 496 t. Full Load
Dimensions: 166.55 m long, 21.90 m wide, 8.04 m draft
Machinery: 2 steam turbines, 4 boilers, 52,000 hp.
Top speed: 23 knots
Armament: 8 x 127 AA, 24 x 25 mm AA, 24 aircraft
IJN Shinyo in 1945
IJN Shinyo was converted from the 1934 German liner SS Scharnhorst, stuck in Japan and requisitioned with the consent of Berlin. In February 1942, work started in Kure, and she was completed in December 1943. Larger, she carried many more planes than other Japanese escort carriers, and she was also the heaviest. Her construction made use of the steel reserved for the construction of No. 111, the third unit of the unfinished Yamato class, due to unsufficient reserves. She made various missions in 1944 before receiving in June fifty 25 mm AA. Finally, she was sunk on November 17, 1944, by the sub USS Spadefish.
Displacement: 17,500 t. standard -20 586 t. Full Load
Dimensions: 189.36 m long, 25.60 m wide, 8.18 m draft
Machinery: 2 steam turbines, 4 boilers, 26,000 hp.
Top speed: 22 knots
Armament: 8 x 127 AA, 30 x 25 mm AA, 33 aircraft
This aircraft carrier never completed was based on a cruiser hull of a modified mogami class, converted after launch in May 1943. Conversion work started at Sasebo in November and she had two lift servicing a single hangar. However conversion was never completed. IJN Ibuki was 80% complete in March 1945 when work stopped. In addition to a large AA artillery, Ibuki innovated with six anti-aircraft rocket launchers (168 in all) that should have erected a steel barrier impassable to US aviation. Her aicraft fleet was limited, which was of little importance at the end of 1944, fordue to the lack of fuel and pilots.
Displacement: 12,500 t. standard -14 570 t. Full Load
Dimensions: 198.35 m long, 21.20 m wide, 6.31 m draft
Machinery: 2 steam turbines, 4 boilers, 72,000 hp.
Top speed: 29 knots
Armament: 4 x 127 AA, 48 x 25 mm AA, 6 x 28 launch rockets, 30 grenades ASM, 27 aircraft