Japanese Naval Bombers and Missiles

Medium Attack Bombers

Historical note: Japan came late to the concept of the fast medium bomber and only introduced the type during the mid-1940s. The type was originally assigned to bombing coastal naval bases and installations plus medium-range shipping attack using bombs and torpedoes. Over the years, as Japan’s carrier fleet declined, the land-based medium attack bombers gradually replaced the carriers as the Japanese Navy’s primary striking arm and the type slowly merged with the short-ranged single-engined attack aircraft. In 1966, the medium-range attack category was finally abolished and the aircraft were merged with the theoretically carrier-based short range attack aircraft to form a class structured to provide medium-range (theater) strategic bombers tasked with regional (ie anti-Triple Alliance) operations. The classic medium bomber concept carried on as an Army responsibility.

Yokosuka P1Y Ginga, CADS Reporting Name Keith Design of the P1Y Ginga was started in 1940 in response to a specification demanding a fast medium bomber capable of undertaking low- and medium altitude attacks as well as dive and torpedo bombing. The first prototype flew in August 1943 but the aircraft proved extremely unreliable and correcting its many deficiencies took until early 1945. Eventually, its bugs ironed out, the P1Y proved to be a valuable and successful aircraft and it remained in service until 1955.

Mitsubishi P2M Hiryu, CADS Reporting Name Ike. The delays to the P1Y lead the Navy to investigate the possibility of acquiring the Army’s Ki-67 Hiryu as a gap-filler. Mitsubishi produced a version of the Ki-67 for Navy use, differing mainly in having provision for a torpedo. The P2M entered service in 1944 and served alongside the P1Y until 1953.

Mitsubishi P3M Yasukuni, CADS Reporting Name Dick The Germans designed the Heinkel 274 as a high-altitude bomber version of the He-177 but the type fell foul of Goering’s decision to terminate all heavy bomber production and the German prototypes were never flown. The machine tooling and blueprints plus a large quantity of components were supplied to Japan. Mitsubishi took the design over and flew the first prototype in 1945. It proved to be an extremely complex and demanding aircraft although its service ceiling of 47,000 feet made it attractive for the reconnaissance role. Only a limited number of P3M aircraft were built and the type’s unreliability gave it a short service life. It entered service in 1948 and had been withdrawn by 1951.

Yokosuka P4Y Byakko, CADS Reporting Name Leon The P1Y1 was a very well-designed aircraft that was cursed with unreliable powerplants. The obvious solution was to re-engine the aircraft; Yokosuka took this opportunity to produce the Japanese Navy’s first jet-engined bomber. The two piston engines were replaced with a pair of Ne-130 engines, each generating 2,002 pounds of thrust. The conversion proved to be highly successful, the sleek airframe of the P1Y taking full advantage of the limited power of the jets and boosting maximum speed to over 400mph. Range, of course, fell dramatically but the sacrifice was considered worthwhile. The prototype P4Y first flew in 1946 and the type entered service in late 1947. Even that rate of development meant that the aircraft was partly outdated by that time and the type was quickly relegated to training duties when the more advanced P5Y entered service.

Yokosuka P5Y Kyokko, CADS Reporting Name Mike The P4Y was a good first step but it became obvious something better was required. It was underpowered and its tailwheel undercarriage was unsuited to jet operations. Accordingly, a thorough redesign was carried out. The single underwing Ne-130s were replaced by a paired installation, doubling the available thrust. The wings were redesigned to accommodate two large wingtip tanks. Most importantly, the fuselage was enlarged and the center of gravity shifted so that the aircraft could be equipped with a nosewheel undercarriage. The P5Y first flew in late 1948 and entered service by the end of 1949. Despite its very short range and limited payload, it remained in Japanese Navy service until 1955.

Yokosuka P6Y Gyoku, CADS Reporting Name Nate The P6Y was, perhaps the definitive development of the line of development that had started with the P1Y. The P5Ys four Ne-130 engines were obsolescent, fuel-thirsty and underpowered. By 1950, Ne-50 engines developing 4,400 pounds of thrust were available. Thus one Ne-50 developed more thrust than two Ne-130s while burning less fuel. Two Ne-50 engines therefore replaced the four Ne-130s of the P5Y and were mounted on a new, thin-profile wing. The result was a great improvement over the P5Y. Maximum range went up to 1,750 miles while maximum speed was increased to 560 miles per hour. Payload was doubled to 4,400 pounds of bombs. The P6Y first flew in 1951 and it entered squadron service in 1953. It first replaced the old P2M bombers, then the P1Y and P5Y. By 1957, the P6Y had become the Chipanese Navy’s standard medium range bomber. It remained in Chipanese service until 1975. It was exported to The Caliphate from 1956 onwards and Caliphate P6Ys remained in service until the mid-1990s.

Yokosuka P7Y Geico, CADS Reporting Name Orace With the P6Y, Yokusuka had established themselves as the pre-eminent medium bomber designers in Japan. As P6Y production ramped up, the group started work on a successor intended as an insurance policy against that position being lost. Although their next design had a clear family resemblance to the P6Y, it was an entirely new aircraft. It had a crew of three, a pilot and navigator sitting under a fighter-style bubble cockpit jest ahead of the steeply-swept wings and a bombardier in the long glazed nose. The P7Y was unequivocally designed to deliver tactical nuclear weapons; although it had a theoretical bombload of 4,400 pounds, this was never regarded as anything more than a reserve option. The P7Y was a further great improvement in performance. The aircraft had a maximum speed of 702 miles per hour and could reach a service ceiling of 59,500 feet. It entered service in 1958 and remained in use until the early 1980s.

Yokosuka P8Y Denko, CADS Reporting Name Quill The P8Y was a refined and upgraded derivative of the P7Y. Bombload was increased to 6,600 pounds and a new radar bombing-navigation system was installed. Maximum speed was increased to 1,250 miles per hour, making the P8Y the fastest bomber in Chipanese service at the time. Service ceiling was 53,200 feet. The P8Y entered service in 1963 but its career in Chipanese naval aviation was very short. When the Showa Restoration Coup took place in 1965, the Japanese Army took over all medium bomber forces. As a result, in 1966, the existing Navy medium bombers were absorbed into the B-category as medium-range strategic aircraft. The P8Y was, however, not part of this reorganization. All P8Y aircraft were taken over by the Army and used to re-equip Japanese Army medium bomber groups, many of which were still flying Ki-127 aircraft. The P8Y was the last Japanese Navy medium bomber produced.

Flying Boats

Historical note: Japanese possession of large numbers of small Pacific islands meant that its development of a powerful flying boat fleet was almost inevitable. Initially, these aircraft served as maritime surveillance and bomber assets but their role quickly expanded to include transport. By the mid-1950s, the Japanese realized that the United States had no intention of fighting their way across the Pacific, taking each island garrison in turn. Instead, they would simply find those garrisons and drop atomic bombs on them. The only defense against that form of attack was not to be there when the bombs went off. The Chipanese forces thus evolved the concept of what they called “Flying Garrisons”. These constituted a group of flying boats carrying an infantry defense group and coastal defense missiles along with a unit of seaplane fighters for air cover and additional cargo-carrying flying boats loaded with fuel and supplies. These could move to any unoccupied atoll and set up a reasonably solid defense within a few hours. More importantly, they could evacuate that atoll base even more quickly. Thus, they could fight a mobile war, moving from base to base as operational necessity demanded, if necessary, ones far in the enemy rear. This concept was, of course, never tested against American forces but “Flying Garrisons” were used in the Guano War to some marked effect.

Yokosuka H5Y A medium-sized twin engined flying boat, this aircraft was underpowered and its production was limited to 20. It spent all its years of service in obscure training duties and never saw operational service.

Kawanishi H6K, CADS Reporting Name Fresco A very large, four-engined flying boat, the H6K marked a new advance in flying boat design. It entered service in mid-1938 and its fabulous endurance made it immediately successful as a maritime patrol aircraft. The H6K was occasionally used as a bomber during the early days of the China Campaign but its lack of protection and huge fuel tanks made it too vulnerable for this to be continued. After being replaced in front-line service by the H8K, the remaining H6Ks were converted to transports (under the designation H6K5-L) and played a valuable role in developing the “Flying Garrison” concept. The H6K5-L transports soldiered on, many as civilian aircraft, until 1957. A historical oddity is that the original Reporting Name of this aircraft was Frisco after a B-movie cowboy hero. However, the city council of San Francisco objected vociferously to having their city name “associated with militarism” and the aircraft was renamed Fresco. For some reason the habit stuck and all Japanese flying boats were given codenames starting with F.

Yokosuka H7Y In the pursuit of more range and endurance, Yokosuka took their abortive H5Y and enlarged it to four engines. They also adopted the Junkers Jumo diesel engine as the primary power plant, ending up with an aircraft with a range of over 6,000 miles and an endurance of 40 hours. Despite this performance, the Japanese navy were reluctant to adopt diesel engines for aircraft propulsion and only a single prototype H7Y was built.

Kawanishi H8K Seiku, CADS Reporting Name Farmer Perhaps the definitive Japanese flying boat the H8K first flew in December 1940. It corrected all the deficiencies of the H6K, being heavily armed with 20mm cannon in power-operated turrets, could carry 4,400 pounds of bombs and was also well-armored. It was capable of almost 300mph and had a range of over 4,500 miles with an endurance of 24 hours. Despite some early teething troubles, the aircraft entered service in January 1942, starting a career that was to last for more than twenty years. Even after its retirement form military service in 1963, the H8K, in its H8K6-L transport form, was to continue in service as a civilian passenger transport in Chipan’s Pacific Island territories and the type can still be seen today in this role.

Aichi H9A Intended to act as a training aircraft for the large H6K and H8K flying boats, the H9A was built in very limited numbers and its operational career was spent entirely within Japanese coastal waters.

Hiro H10H Another attempt to build a medium-sized flying boat, the twin-engined Hiro H10H1 was quite successful having relatively good performance and could tolerate operations of rough seas. However, an analysis of costs showed that it was only marginally less costly than the bigger and much more useful four-engined flying boats. However, the H10H was of significance in that the production run of five aircraft was used to develop Japanese operational doctrine for the use of flying boats in an anti-submarine role.

Kawanishi H11K Seiku, CADS Reporting Name Fargo. The success of the H6K and H8K flying boats in the transport role lead Kawanishi and the Japanese Navy to develop a new flying boat optimized for transport duties. Taking the H8K as a base, the aircraft was re-engined with four Nakajima Ha-54 engines developing 3,800 horsepower, more than twice the output of the earlier engines. The wings were enlarged by approximately 30 percent and mated to a modified fuselage. This was wider and flatter than that of the H8K and had a single vehicle deck rather than two passenger decks as on the H8K. However, its added size increased the usable cargo space by about 20 percent. In order to keep the wing high enough above the water, it was mounted across the top of the fuselage, being covered by a fairing that gave the H11K its popular nickname of “Hunchback”. The greatest change though was in the nose. This consisted of a pair of clamshell doors with an integral loading ramp that could be extended and retracted to land the aircraft’s cargo. The H11K1 first flew in 1947 and the type entered service in 1949. It was an immediate worldwide success with aircraft of the type being exported to South America and South Africa. A civilian version entered production in 1955 and was also a commercial success. The civilian H11Ks were even sold to Europe, the best known operator of the type being Sir Freddy Laker’s Airferry Line. Previously, British civilians wanting to take their cars to Europe had to drive to a port, load their cars on a car ferry and then drive from the French ports to their destination. Using the Airferry H11Ks, they simply loaded their cars only the flying boat in London Docklands or Southampton and could fly direct to Rome, Sweden or to the burgeoning tourist resorts along Russia’s Black Sea coast. This proved so popular that Sir Freddy Laker became a millionaire on the profits. The H11Ks remained in military service until 1971 when they were replaced by the later H13K. Civilian H11Ks remained a common sight around the world well into the 1980s and are still used in less well-travelled areas today.

Kawanishi H12K Seiku-kai, CADS Reporting Name Forrester The successful design of the H11K lead Kawanishi to suggest similar modifications to the H8K to produce a general-service complement to the transport-optimized H11K. The engine change was more drastic than planned; the radial engines on the H8K were replaced by NT-30 turboprops rated at 6,650 ehp. The fuselage was made shallower and lengthened with the wing being mounted in a fuselage-top “hump” as on the H11K. For all these changes, the aircraft was still recognizably derived from the H8K. It was, however, almost 100mph faster and carried twice the bombload of the earlier aircraft while retaining its long range and endurance. The H12K first flew in 1958 and entered service in 1961, replacing the H8Ks. They participated in the “Guano War” with Australia, leading to some surrealistic “dogfights” between Chipanese and Australian flying boats. H12K aircraft are still in service with the Japanese Air Force and the type remains in limited production.

Kawanishi H13K Seiku-kai, CADS Reporting Name Flogger. Just as results from the development of the H11K had been used to produce the H12K, so advances resulting from the design of the general-purpose H12K were fed into the transport flying boat H13K. This had a further redesigned and enlarged wing mounting NT-30/6 turboprops developing 7,100 ehp. Experience with the H11K had suggested the aircraft “bulked out” before it ‘weighted out” - in short it could not lift its full capacity in weight terms because the fuselage lacked volume. Accordingly the fuselage was lengthened by ten meters and widened slightly. The Japanese by now well aware of the potential for civilian sales of this aircraft introduced the civilian aircraft at the same time as the military version and were rewarded by an immediate order from Laker’s Airferry Line to replace their H11Ks. The prototype H13K flew in 1968 and the type entered service with both the Japanese Navy and Laker Airferry in 1971. Military production ceased in 1988 but civilian production continues with the type being continuously refined and developed with more powerful engines and greater cargo capacity.

Manned Cruise Missiles

Historical note: Japan started developing piloted cruise missiles in 1944 in response to a requirement for a very long-range anti-shipping weapon that could be fired from cruisers. Some early experiments were made with a Japanese development of the German Fi-103 cruise missile. Interestingly, American cruisers were equipped with a similar weapon, the Chelomey Kh-10 around this time, the big difference being that the Americans and Russians used radio control for these weapons, the Japanese decided that this was not accurate enough and made provision for a pilot. The Japanese were not impressed by the Fi-103 (which was an inferior design to the superficially similar Kh-10) and decided they could do better. The result was the Ohka series of piloted cruise missiles. Development was on a very low key until the early 1950s when it was dramatically accelerated to provide a delivery system for Japan’s atomic weapons. Originally “Ohka” was the name for the first missile in this series but it quickly became a generic name for all Chipanese strategic piloted cruise missiles. Also, perhaps reflecting some strange aspect of nation psychology, the Japanese never used remote control or automatic guidance systems for their strategic missiles even though they developed these for their long-range tactical anti-ship missiles. They preferred to have their strategic nuclear weapons flown by a pilot - and even today this is still the case. The MXY-7 to MXY-10 flew direct to their targets allowing for maneuvers to avoid defenses on their way in. The MXY-11 onwards climbed to high altitude after launch and flew in at altitudes of around 100,000 feet before diving on their targets. Note that there are some sub-variants to each series; for example, the Ohka-51 was designed for launch from the G10N while the Ohka-52 was launched from the G11N.

Yokosuka MXY-7 Ohka-10. Introduced 1948, powered by three rocket engines, range 25 miles, speed 403 mph. Warhead 2,600 pounds explosive. Launched from aircraft

Yokosuka MXY-7 Ohka-20. Introduced 1949, powered by Ne-20 jet engine, range 80 miles, speed 290 mph, warhead 1,350 pounds explosive. Launched from aircraft

Yokosuka MXY-7 Ohka-30.Introduced 1950, powered by Ne-130 jet engine, range 175 miles, speed 345 mph, warhead 1,750 pounds explosive. Fired from catapult on submarines.

Yokosuka MXY-8 Ohka-40. Introduced 1955, powered by Ne-80 jet engine, range 350 miles, speed 550mph, nuclear warhead. Launched from G10N bomber.

Yokosuka MXY-8 Ohka-50. Introduced 1955, powered by Ne-80 jet engine, range 200 miles, speed 550 mph, nuclear warhead. Launched from I-401 class SSGs and later designs.

Yokosuka MXY-9 Ohka-60. Introduced 1960, powered by two Ne-80 jet engines, range 300 miles, speed 850 mph, thermonuclear warhead, launched from Japanese navy strategic bombers.

Yokosuka MXY-9 Ohka-70. Introduced 1960, powered by two Ne-80 jet engines, range 200 miles, speed 850 mph, thermonuclear warhead, launched from Japanese Navy SSGs.

Yokosuka MXY-10 Ohka-80. Introduced 1972, powered by two Ne-90 jet engines, range 600 miles, speed 1,350 mph, thermonuclear warhead, launched from Japanese Navy strategic bombers.

Yokosuka MXY-10 Ohka-90. Introduced 1972, powered by two Ne-90 jet engines, range 400 miles, speed 1,350 mph, thermonuclear warhead, launched from Japanese Navy SSGs

Yokosuka MXY-11 Ohka-100. Introduced 1976, powered by two Ne-90 jet engines, range 900 miles, speed 1,550 mph (2,250 in terminal dive), thermonuclear warhead, launched from Japanese Navy strategic bombers.

Yokosuka MXY-11 Ohka-110. Introduced 1976, powered by two Ne-90 jet engines, range 500 miles, speed 1,550 mph (2,250 in terminal dive), thermonuclear warhead, launched from Japanese Navy SSGs and SSGNs

Yokosuka MXY-12 Ohka-120. Introduced 1985, powered by two Ne-95 jet engines, range 1,500 miles, speed 1,850 mph (2,350 in terminal dive), thermonuclear warhead, launched from Japanese Navy strategic bombers.

Yokosuka MXY-11 Ohka-130. Introduced 1985, powered by two Ne-95 jet engines, range 1,250 miles, speed 1,850 mph (2,350 in terminal dive), thermonuclear warhead, launched from Japanese Navy SSGNs


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