Category Archives: Imperial Navy Air Force

Japan

Nakajima E8N2 ‘Dave’, Training Unit, Kyushu (Wings Models, Vacu-formed)

TYPE: Ship-borne reconnaissance floatplane, Trainer

ACCOMMODATION: Crew of two

POWER PLANT: One Nakajima Kotobuki 2 KAI 2 radial engine, rated at 630 hp

PERFORMANCE:  186 mph

COMMENT: The Nakajima E8N was developed as a replacement for the same company’s E4N and was essentially an evolutionary development of the earlier type, with revised wings of lesser area and taller tail surfaces. Seven prototypes were constructed, under the company designation MS, first flying in March 1934. These were duly engaged in comparative trials against competitors from Aichi and Kawanishi.
The MS was ordered into production, designated Navy Type 95 Reconnaissance Seaplane Model 1 in October 1935. A total of 755 E8Ns were built by Nakajima and Kawanishi, production continuing until 1940. Operating as a catapult-launched reconnaissance aircraft the E8N was subsequently shipped aboard all the capital ships then in service, battleships, cruisers and aircraft tenders. It was used successfully in the Second Sino-Japanese War and distinguished itself on several occasions by destroying opposing Chinese fighters. Occasionally the aircraft was operated as a dive-bomber but was more often employed as a reconnaissance and artillery spotting aircraft.
One E8N was purchased in early 1941 by the German Naval Attaché to Japan, Vice-Admiral Wenneker, and dispatched on board “KM Münsterland” to rendezvous with the German auxiliary cruiser “Orion” at Maug Island in the Marianas. The meeting occurred on 1 Feb 1941, and “Orion” thus became the only German naval vessel of the Second World War to employ a Japanese float plane.
Some aircraft remained in service with the fleet at the outbreak of the Pacific War, and one flew reconnaissance from the battleship Haruna during the Battle of Midway. The type was coded “Dave” by the Allies. Later, they were replaced by more modern aircraft such as the Aichi E13A and the Mitsubishi F1M and the remaining aircraft were reassigned to second-line duties for instance communications, liaison and training (Ref.: 24).

Kawanishi E7K2 (“Alf”), (Tamiya)

TYPE: Reconnaissance floatplane

ACCOMMODATION: Crew of three

POWER PLANT: One Mitsubishi “Zusei” 11 radial engine, rated at 870 hp

PERFORMANCE: 171 mph

COMMENT: The Kawanishi E7K was a Japanese 1930s three-seat reconnaissance floatplane. It was allocated the reporting name “Alf” by the Allies of WW II.
In 1932 the Imperial Japanese Navy requested the Kawanishi Aircraft Company to produce a replacement for the company’s Kawanishi E5K. The resulting design, designated the Kawanishi E7K1, was an equal span biplane powered by a 620 hp “Hiro Type 91W-12 liquid-cooled inline engine. The first aircraft flew on 6 February 1933 and was handed over to the navy for trials three months later. It was flown in competition with the Aichi AB-6 which was designed to meet the same 7-Shi requirement. The E7K1 was ordered into production as the Navy Type 94 Reconnaissance Seaplane and entered service in early 1935. It became a popular aircraft, but was hindered by the unreliability of the “Hiro” engine. Later production E7K1s were fitted with a more powerful version of the “Hiro 91”, but this did not improve the reliability. In 1938 Kawanishi developed an improved E7K2 with a Mitsubishi “Zuisei 11” radial engine. It first flew in August 1938 and was ordered by the Navy as the Navy Type 94 Reconnaissance Seaplane Model 2. The earlier E7K1 was renamed to Navy Type 94 Reconnaissance Seaplane Model 1.
The type was used extensively by the Japanese Navy from 1938 until the beginning of the Pacific War, when E7K1 were relegated to training duties but the E7K2, despite their obsolescence, remained in first-line service until 1943. The aircraft was initially used for convoy escort, anti-submarine patrol and reconnaissance. Later in the war, the E7K2s were retained in the liaison and training role and as mother aircraft for the MXY4 radio-controlled target plane. Also both versions were used in Kamikaze operations in the closing stages of the war (Ref.: 1, 24).

Yokosuka K5Y2 (“Willow”)

TYPE: Intermediate trainer

ACCOMMODATION: Crew of two

POWER PLANT: One Hitachi “Amakaze” radial engine, rated at 300 hp

PERFORMANCE: 132 mph

COMMENT: The Yokosuka K5Y2 was a two-seat unequal-span biplane trainer (Allied reporting name “Willow”) that served in the Imperial Japanese Navy during World War II. Due to its bright orange paint scheme (applied to all Japanese military trainers for visibility), it earned the nickname “Red dragonfly”, after a type of insect common throughout Japan.
The aircraft was based on the Yokosuka Navy Type 91 Intermediate Trainer, but stability problems led to a redesign by Kawanishi in 1933. It entered service in 1934 as Navy Type 93 Intermediate Trainer K5Y1 with fixed tail-skid landing gear, and remained in use throughout the war. Floatplane types K5Y2 and K5Y3 were also produced. After the initial 60 examples by Kawanishi, production was continued by Watanabe (556 aircraft built), Mitsubishi (60), Hitachi (1,393), First Naval Air Technical Arsenal (75), Nakajima (24), Nippon (2,733), and Fuji (896), for a total of 5,770. These aircraft were the mainstay of Imperial Japanese Navy Air Service’s flight training’s, and as intermediate trainers, they were capable of performing demanding aerobatic maneuvers. Two further land-based versions, the K5Y4 with a 480 hp “Amakaze” 21A engine and the K5Y5 with a 515 hp “Amakaze” 15, were projected but never built.
A K5Y of the Kamikaze Special Attack Corps 3rd Ryuko Squadron was credited with sinking the destroyer USS Callaghan on July 29, 1945, the last US warship lost to kamikaze attack during the war (Ref.: 24).

M6A1-K “Nanzan” (“South Mountain”), (‘Shisei-Seiran Kai), (MPM-Models)

TYPE: Trainer aircraft for Aichi M6A1 “Seiran”

ACCOMMODATION: Pilot and trainer

POWER PLANT: One Aichi Atsuta Type 32 liquid-cooled engine, rated at 1,400 hp

PERFORMANCE: 310 mph at 17,060 ft

COMMENT:  The Aichi M6A1-K “Seiran Kai” was a trainer version of the submarine-launched attack floatplane Aichi M6A1 “Seiran”. It was fitted with an inwardly-retracting undercarriage, and the folding tip of the rudder was dispensed with as the absence of floats improved directional stability. The popular name of the M6A1-K was later changed to “Nanzan” (Southern Mountain”).
Two prototypes of this aircraft were built and flight tested before the war in the Pacific ended in 1945 (Ref.: 24).

Mitsubishi A7M2 “Reppū” (“Strong Gale”, “Sam”), (MPM Models)

TYPE: Carrier-borne and land-based fighter

ACCOMMODATION: Pilot only

POWER PLANT: One Mitsubishi Ha-43 radial engine, rated at 2,200 hp

PERFORMANCE: 390 mph at 21,660 ft

COMMENT: Towards the end of 1940, the Imperial Japanese Navy asked Mitsubishi to start design on a 16-Shi carrier-based fighter, which would be the successor to the carrier-based Mitsubishi A6M “Rei-sen” (“Zeke”, Allied reporting code “Zero”). At that time, however, there were no viable high-output, compact engines to use for a new fighter. In addition, Mitsubishi’s design’s team was preoccupied with addressing early production issues with the A6M2b as well as starting development on the A6M3 and the 14-Shi interceptor which would later become the Mitsubishi J2M “Raiden” (Allied code “Jack”), a land-based interceptor built to counter high-altitude bombers). As a result, work on the “Rei-sen” successor was halted in January 1941.
In April 1942, the development of the A6M3 and the 14-Shi interceptor was complete, and the Japanese Navy once again tasked Mitsubishi with designing a new “Zero” successor to become the “Navy Experimental 17-Shi Ko (A) Type Carrier Fighter “Reppu” (“Strong Gale”, Allied reporting code “Sam”). In July 1942 the Navy issued specifications for the fighter: it had to fly faster than 397 mph above 20,000 ft, climb to 20,000 ft in less than 6 minutes, be armed with two 20 mm cannon and two 0.51 in machine guns, and retain the maneuverability of the A6M3 “Rei-sen”.
As before, one of the main hurdles was engine selection. To meet the specifications the engine would need to produce at least 2,000 hp, which narrowed choices down to Nakajima’s NK9 (Ha-45) under development (later becoming “Homare”), or Mitsubishi’s MK9 (Ha-43), which was also still being developed. Both engines were based on 14-cylinder Nakajima “Sakae” and Mitsubishi “Kinsei”, respectively) engines converted to 18-cylinder power plants. The early NK9 had less output but was already approved by the Navy for use on the Yokosuka P1Y “Ginga” (Allied code “Frances”), while the larger MK9 promised more horsepower.
With the larger, more powerful engine, wing loading became an issue. With the MK9 the engineers concluded it could fulfill the requirements; however, production of the MK9 was delayed compared to the NK9, and the Japanese Navy instructed Mitsubishi to use the NK9.
Work on the 17-Shi was further delayed by factories prioritizing Mitsubishi  A6M “Reisen” and Mitsubishi G4M (Allied code “Betty”) bomber production as well as further work on A6M variants and addressing Mitsubishi J2M “Raiden” issues. As a result, the 17-Shi, which became the A7M1, officially flew for the first time on 6 May 1944, four years after development started. The aircraft demonstrated excellent handling and maneuverability, but was underpowered as Mitsubishi engineers feared, and with a top speed similar to the A6M5 “Rei-sen”/”Zeke”. It was a disappointment, and the Navy ordered development to stop on 30 July 1944, but Mitsubishi obtained permission for development to continue using the Ha-43 engine, flying with the completed Ha-43 on 13 October 1944. The Mitsubishi A7M2 “Reppu” now achieved a top speed of 390 mph, while climb and other areas of performance surpassed the “Zero”, leading the Navy to change its mind and adopt the aircraft. The A7M2 “Reppu” was also equipped with automatic combat flaps, used earlier on the Kawanishi N1K-J “Shiden” (Allied code “George”), significantly improving maneuverability.
In June 1945, ace pilot Saburo Sakai was ordered to Nagoya to test the airplane. He declared it to be the fastest fighter he had ever seen, able to surpass anything on the air, Japanese or American. He claimed it could fly in circles, while ascending, around a Grumman F6F “Hellcat” or a North American P-51 “Mustang”, and that engineers stated it could fight at up to 39,370 ft.
When the war in the Pacific area ended a total of 10 Mitsubishi A7M “Reppu’s” were built including only one production aircraft A7M2 (Ref.: 24).

Kawanishi H8K2 “Type 2 Flying Boat, Model 12“, (Nishiki Hikōtei 12-gata), (“Emiliy”), 901st. Naval Air Corps_Combined Maritime Escort Force, (Hasegawa)

TYPE: Long-range Maritime Reconnaissance and Bomber Flying Boat

ACCOMMODATION: Crew of ten

POWER PLANT: Four Mitsubishi MK4Q “Kasei 22” radial engines, rated at 1,380 hp each

PERFORMANCE: 290 mph at 16,400 ft

COMMENT: The Kawanishi H8K “ Type 2 Large-sized Flying Boat) was an Imperial Japanese Navy flying boat used during WW II for maritime patrol duties. The Allied reporting name for the type was “Emily”.
At the same time the type’s predecessor, the Kawanishi H6K, was going into service in 1938 the Navy ordered the development of a larger, longer-ranged patrol aircraft under the designation “Navy Experimental 13-Shi Large-size Flying Boat”. The result was a large, shoulder-winged design that is widely regarded as the best flying boat of the war. Despite this, initial development was troublesome, with the prototype displaying terrible handling on the water. Deepening of the hull, redesigning of the planing bottom and the addition of spray strips under the nose rectified this. Two further prototypes— actually pre-production aircraft— joined the development program in December 1941. The IJNAF accepted the first production version as the H8K1, “Navy Type 2 Flying Boat, Model 11”, of which 14 would be built.
The H8K1 entered production in 1941 and first saw operational use on the night of 4 March 1942 in a second raid on Pearl Harbor. Since the target lay out of range for the flying boats, this audacious plan involved a refueling by submarine, some 900 km north-west of Hawaii. Two planes from the Yokohama Kokutai (Naval Air Corps) attempted to bomb Pearl Harbor, but, due to poor visibility, did not accomplish any significant damage.
Six days after the second Pearl Harbor raid one of the “Emily’s” was sent on a daylight photo-reconnaissance mission of Midway Atoll. It was intercepted by radar directed Brewster F2A-3 “Buffalo” fighters of Marine Corps squadron VMF-221 and shot down.
After serving as an engine test bed for the Kasei 22 powered H8K2, the original H8K1 experimental aircraft was again modified as the prototype for a transport version of the H8K series. The deep hull made possible the installation of two decks, the lower deck extending from the nose to the rear hull step and the upper extending from the wing centre-section to the rear of the hull. Accommodation was provided for either twenty-nine passengers or sixty-four troops, the armament was reduced to one flexible 13mm Type 2 machine gun in the nose turret and one 20 mm Type 99 Model 1 cannon in the tail turret. A total of thirty-six H8K-2L transport flying boat “Seiku” (“Clear sky) were built between 1943 and 1945 and exclusively operated by Naval transport units.
An improved version of Kawanishi H8K2 “Type 2 Flying Boat, Model 12” (Nishiki Hikōtei 12-gata) soon appeared, and it’s extremely heavy defensive armament earned it deep respect among Allied aircrews. The H8K2 was an upgrade over the H8K-1, having more powerful engines, slightly revised armament, and an increase in fuel capacity. They were used on a wide range of patrol, reconnaissance, bombing, and transport missions throughout the Pacific war. In mid 1943, many aircraft were equipped with Mark IV Model 1 ASV radar. This was to be the definitive variant, with 112 aircraft produced.
Even though far fewer Kawanishi H8Ks were built than contemporary British Short “Sunderlands” or American Consolidated PBY “Catalinas”, the Japanese flying-boat emerged from conflict as the most outstanding water-based combat aircraft of the second World War (Ref.: 1, 24).

Aichi B7A1 ‘Ryusei’ (“Shooting Star”, “Grace”), (Fujimi Models)

TYPE: Carrier-borne torpedo- and dive bomber

ACCOMMODATION: Crew of two

POWER PLANT: One Nakajima NK9B “Homare 11” radial engine, rated at 1,560 hp at 21,000 ft

PERFORMANCE: 367 mph

COMMENT: The Aichi B7A “Ryusei” (“Shooting Star”, Allied reporting name “Grace”) was a large and powerful carrier-borne torpedo-dive bomber produced by Aichi Kokuki KK for the Imperial Japanese Navy Air Service during the Second World War. Built in only small numbers and deprived of the aircraft carriers it was intended to operate from, the type had little chance to distinguish itself in combat before the war ended in August 1945.
The B7A “Ryusei” (originally designated AM-23 by Aichi) was designed in response to a 1941 16-Shi requirement issued by the Imperial Japanese Navy Air Service for a carrier attack bomber that would replace both the Nakajima B6N “Tenzan” torpedo plane and the Yokosuka D4Y “Suisei” dive bomber in IJN service. It was intended for use aboard a new generation of “Taihō”-class aircraft carriers, the first of which was laid down in July 1941. Because the deck elevators on the “Taihōs” had a larger square area than those of older Japanese carriers, the longstanding maximum limit of 11 m (36 ft) on carrier aircraft length could now be lifted.
The Aichi’s designers chose a mid-wing arrangement for the B7A to provide for an internal bomb-bay and to ensure enough clearance for the plane’s 3.5 m four-bladed propeller. This in turn necessitated the adoption of an inverted gull wing, reminiscent of the Vought F4U “Corsair”, in order to shorten the length of the main landing gear. The wing featured extendable ailerons with a ten-degree range of deflection, enabling them to act as auxiliary flaps. Dive brakes were fitted underneath just outboard of the fuselage. The B7A’s outer wing panels were designed to fold upwards hydraulically for carrier stowage, reducing its overall span from 14.4 m to approximately 7.9 m.
Selection of a power plant was dictated by the Japanese Navy which requested that Aichi design the aircraft around the 1,825 hp Nakajima NK9C “Homare 12” 18-cylinder two-row air-cooled radial engine. This was expected to become the Navy’s standard aircraft engine in the 1,800 hp to 2,200 hp range.  The B7A had a weight-carrying capacity stemming from its requirements, resulting in a weapons load no greater than its predecessors. The presence of an internal bomb bay with two high-load-capability attachment points allowed the aircraft to carry two 250 kg or six 60 kg bombs. Alternatively, it could carry a single externally mounted Type 91 torpedo, weighing up to 848 kg.
Defensive armament initially consisted of two 20mm Type 99 Model 2 cannons in the wing roots and one flexible 7.92mm Type 1 machine-gun mounted in the rear cockpit. Later production models of the B7A2 featured a 13mm Type 2 machine-gun in place of the 7.92mm gun.
Despite the plane’s weight and size, it displayed fighter-like handling and performance, besting the version of the Mitsubishi A6M “Zero” in service at the time. It was fast and highly maneuverable.
Given the codename “Grace” by the Allies, the B7A1 first flew as a prototype in May 1942, but teething problems with the experimental NK9C “Homare” engine and necessary modifications to the airframe meant that the type did not enter into production until two years later in May 1944. Nine prototype B7A1s (the second prototype is shown here)  were built and were progressively modified to eradicate minor airframe and equipment problems.
In April 1944 an improved engine version, the 1,825 hp “Homare 12”, became available and powered by this engine the aircraft was finally placed in production as the Aichi B7A2 “Ryusei” (Ref.: 24).

Mitsubishi A6M5c ‘Rei-sen’ (“Zero”, “Zeke”), (Hasegawa)

TYPE: Carrier-borne fighter, fighter-bomber

ACCOMMODATION: Pilot only

POWER PLANT: One Nakajima NK1F “Sakae 21” radial engine, rated at 1,100 hp at 9,350 ft

PERFORMANCE: 351 mph at 19,685 ft

COMMENT: The Mitsubishi A6M “Zero” was the best known Japanese warplane of WW II. A6M “Zeros” were predominantly used by the Imperial Japanese Navy Air Service (IJN) on aircraft carriers, and also by its land-based fighter units. At the start of the Pacific War in 1941, the A6M constituted about 60% of the IJN fighter force. It took part in carrier operations throughout much of the Pacific Ocean, as well as over the northeast Indian Ocean
The Mitsubishi A6M “Zero” is a long-range fighter aircraft formerly manufactured by Mitsubishi Aircraft Company. Officially, the A6M was designated as the Mitsubishi Navy Type 0 carrier fighter (“Rei-shiki-kanjō-sentōki”), or the Mitsubishi A6M “Rei-sen”. The A6M was usually referred to by its pilots as the “Reisen” (Zero fighter), “0” being the last digit of the Imperial Year 2600 (1940) when it entered service with the Imperial Navy. The official Allied reporting name was “Zeke”, although the use of the name “Zero” was later adopted by the Allies as well.
The “Zero” was considered the most capable carrier-based fighter in the world when it was introduced early in WW II, combining excellent maneuverability and very long range. The IJN also frequently used it as a land-based fighter.
With its low-wing cantilever monoplane layout, retractable, wide-set conventional landing gear and enclosed cockpit, the “Zero” was one of the most modern carrier based aircraft in the world at the time of its introduction. It had a fairly high-lift, low-speed wing with very low wing loading. This, combined with its light weight, resulted in a very low stalling speed of well below 69 mph. This was the main reason for its phenomenal maneuverability, allowing it to out-turn any Allied fighter of the time.
The “Zero” quickly gained a fearsome reputation. Thanks to a combination of unsurpassed maneuverability — even when compared to other contemporary Axis fighters — and excellent firepower, it easily disposed the motley collection of Allied aircraft sent against it in the Pacific in 1941. It proved a difficult opponent even for the British Supermarine “Spitfire”.  Although not as fast as the British fighter, the “Zero” could out-turn the “Spitfire” with ease, sustain a climb at a very steep angle, and stay in the air for three times as long. In early combat operations, the “Zero” gained a legendary reputation as a dogfight achieving an outstanding kill ratio of 12 to 1, but by mid-1942 a combination of new tactics and the introduction of better equipment enabled Allied pilots to engage the “Zero” on generally equal terms. By 1943, due to inherent design weaknesses and an inability to equip it with a more powerful aircraft engine, the “Zero” gradually became less effective against newer Allied fighters. By 1944, with opposing Allied fighters approaching its levels of maneuverability and consistently exceeding its firepower, armor, and speed, the A6M had largely become outdated as a fighter aircraft. However, due to design delays and production difficulties, which hampered the introduction of newer Japanese aircraft models, the “Zero” continued to serve in a front line role until the end of the war in the Pacific. During the final phases, it was also adapted for use in Kamikaze operations.
Japan produced more “Zeros” than any other model of combat aircraft during the war. When the war in the Pacific Area of Action ended, 10,939 aircraft have been built by Mitsubishi Jukogyo K.K. and Nakajima Hikoki K.K. in four major variants A6M2, A6M3, A6M5, and A6M8, each variant including several subtypes. Nakajima built a float-plane variant, the Nakajima A6M2-N, Allied reporting name “Rufe”.
The Mitsubishi A6M5c, Model 52 Hei, featured an armament change: One 13.2 mm Type 3 machine gun was added in each wing outboard of the cannon, and the 7.7 mm gun on the left side of the cowl was deleted. Four racks for rockets or small bombs were installed outboard of the 13 mm gun in each wing. Engine changed to a Nakajima NK1F “Sakae21” although some sources state that the A6M5c had a more powerful “Sakae 31” engine. In addition, a 55 mm thick piece of armored glass was installed at the headrest and an 8 mm thick plate of armor was installed behind the seat. The mounting of the central 300 l (79 US gal) drop tank changed to a four-post design. Wing skin was thickened further. The first of this variant was completed in September 1944 (Ref.: 24).

Kugisho NK-1B (Unicraft, Resin)

TYPE: Interceptor, fighter. Project

ACCOMMODATION: Pilot only

POWER PLANT: One Nakajima NK-1B “Sakae” radial engine, rated at 1,100 hp

PERFORMANCE: No data available

COMMENT: On 26 April 1939, a German Messerschmitt Me 209 V1 set a new world speed record of almost 469 mph. This relative small Me 209 was a completely new aircraft and not to mistake for a replacement of the Messerschmitt Me 109, entering service with the Luftwaffe at the same time. Its only purpose was to set a new speed record.
Impressed by that speed the Imperial Japanese Navy Air Force authorized the Yokosuka Naval Air Technical Arsenal, Yokosuka also known as Kaigun Koku Gijutsusho or Kugisho to propose several designs of similar aircraft. In a complete reversal from previous Japanese Navy requirements priority was given speed, rate of climb, and maneuverability.
One design was built around a Nakajima NK1 “Sakae” radial engine, one of the most powerful engines available in Japan at that time. Another design proposed by Kugisho was the Kugisho HA-40, powered by a Kawasaki Ha-40 liquid-cooled engine derived from the German Daimler-Benz DB 601A. A more powerful variant of this engine was installed in the world record-breaking Messerschmitt Me 209 V1.
Although calculations and designs were in an advanced stage none of the Kugisho projects were realized
Noteworthy is the fact that the Imperial Japanese Army Air Force had similar projects, e. g. the Kawasaki Ki-60.

Aichi M6A “Seiran” (“Mountain Haze”), 631st Kokutai, (MPM Models)

TYPE: Submarine-launched attack floatplane

ACCOMMODATION: Crew of two

POWER PLANT: One Aichi “Atsuka” Type 31 liquid-cooled engine, rated at 1,400 hp

PERFORMANCE: 295 mph at 17,060 ft

COMMENT: To equip the I-400 class submarine aircraft carriers, the Imperial Japanese Navy Air service requested for an attack aircraft with a range of 1,000 mi and a speed of 345 mph. Aichi aircraft company proposed a design on the basis of the Yokosuka D4Y1 “Suisei” that Aichi was already manufacturing under license. The D4Y1 was a relatively small single-engine carrier dive bomber with exceptionally clean lines and high performance. Detailed engineering studies commenced in an effort to modify the “Suisei” for use aboard the I-400 submarines but the difficulties in doing so were eventually judged insurmountable and a completely new design was initiated.
Aichi’s final design, designated M6A1, was a two-seat, low-winged monoplane powered by an Aichi “Atsuka” engine, a license-built copy of the German Daimler-Benz DB 602  liquid-cooled engine. The aircraft was fitted with detachable twin floats to increase its versatility. If conditions permitted, these would allow the aircraft to alight next to the submarine, be recovered by crane and then re-used. The floats could be jettisoned in flight to increase performance or left off altogether for one-way missions. The “Seiran’s” wings rotated 90 degrees and folded hydraulically against the aircraft’s fuselage with the tail also folding down to allow for storage within the submarine’s 11 ft diameter cylindrical hangar.
As finalized, each I-400 class submarine had an enlarged watertight hangar capable of accommodating up to three M6A1s. The “Seirans” were to be launched from an 85 ft compressed-air catapult mounted on the forward deck. A well-trained crew of four men could roll a “Seiran” out of its hangar on a collapsible catapult carriage, attach the plane’s pontoons and have it readied for flight in approximately 7 minutes.
The first of eight prototypes was completed in October 1943, commencing flight testing in November that year. A problem with overbalance of the auxiliary wings was eventually solved by raising the height of the tail fin. Further testing was sufficiently successful for production to start in early 1944.  Owing to the reduced carrier submarine force, production of the “Seiran” was halted, with a total of 28 completed. In mid 1945, it was planned to attack the American base at Ulithi Atoll where forces, including aircraft carriers, were massing in preparation for attacks on the Japanese Home Islands. The flotilla departed Japan on 23 July 1945 and proceeded towards Ulithi. On 16 August, the flagship I-401 received a radio message from headquarters, informing them of Japans surrender and ordering them to return to Japan. All six “Seirans” on board the two submarines, having been disguised for the operation as American planes in violation of the laws of war, were catapulted into the sea with their wings and stabilizers folded (for the  submarine I-401) or pushed overboard (for the submarine I-400) to prevent capture (Ref.: 24).