Japanese Naval Bombers

Dive Bombers

Historical note: Dive and torpedo bombers formed the primary striking arm of the Japanese carriers and their highly-trained, highly motivated crews were arguably the most competent in the world during the early 1940s. However, the absence of naval warfare in the Pacific and the demands of the land war in China forced a concentration on supporting troops in China and this was largely the task of the Army. Naval dive bombers were first to feel the pressure on funding that resulted and their separate existence was terminated when they merged with the torpedo bombers to form a generalized ‘attack” category.

Aichi D3A, CADS Reporting Name Alf The D3A entered service in 1940 and quickly became the Japanese Navy’s primary dive bomber. Relatively fast and agile, its great deficiency was its limited bomb load. In the hands of experts whose criteria was not hitting a ship but where they placed a bomb on that ship, this was acceptable but declining aircrew standards as more and more pilots were drawn away into the Army bomber units in China meant these standards could no longer be maintained and the D3A became too lightly armed for service use. The last had vanished from the fleet by 1944.

Yokusuka D4Y Suisei, CADS Reporting Name Dave Designed as a replacement for the D3A, the D4Y was the only carrier aircraft with a liquid-cooled engine to see service in the Japanese Navy. Severe structural problems limited early production D4Y1 aircraft to reconnaissance roles and the type did not enter service in its design role until 1943. However, problems with the engine continued to hamper reliability and production of the D4Y ceased in 1944 once the in-service D3A squadrons had been re-equipped with new type. The D4Y was withdrawn from service in favor of the D5Y by the end of 1945.

Yokusuka D5Y Suisei-kai, CADS Reporting Name Dave Yokusuka replaced the troublesome liquid cooled engine in the D4Y with a radial engine, this causing a loss in speed but a great increase in reliability. The D5Y entered production during late 1944 and continued to serve on smaller carriers through to 1949. The D5Y was the last specialized dive bomber to be produced for the Japanese Navy.

Attack Bombers

Historical note: This category started out as torpedo bombers but underwent several major changes. The first took place in 1946 when the separate dive bomber category was abandoned and that type merged with torpedo bombers to form the new attack category. Over the years, as Japan’s carrier fleet declined, the attack aircraft operated more and more from land bases and their carrier operability declined. In 1966, any pretense of carrier operability was discarded and this group was restructured to cover the medium-range strategic bombers tasked with regional (ie anti-Triple Alliance) operations.

Nakajima B5N, CADS Reporting Name Bob The B5N torpedo bomber entered service in early 1940, at which time it was considered one of the most advanced torpedo bombers in the world. A stable and accurate aircraft that proved to be an accurate and effective torpedo bomber, the B5N remained the backbone of the Japanese strike squadrons until 1944 when it was replaced by the similar B6N

Nakajima B6N Tenzan, CADS Reporting Name Carl The B6N was very similar to the B5N, differing only in that it had approximately 80 percent more engine power. The B6N suffered from having higher landing speeds and distances compared with the older aircraft and these limited its use to the larger carriers. The B6N was also lightly armed and almost unprotected by 1945 standards and its service career was limited, the last having left the fleet by 1948 after little more than three years active service.

Aichi B7A Ryusei, CADS Reporting Name Ernie. The B7A was designed specifically to rectify the greatest weaknesses of the B6N and B5N, their weak armament and lack of strength. The result was a very strong, heavily-armed torpedo bomber. In fact, the aircraft quickly demonstrated its structural virtues to the point where the Japanese navy realized the aircraft could serve as an effective dive bomber. As a result, the type entered production in 1946 to fill the roles occupied by both the B6N and the D5Y. The older aircraft remained briefly in service on carriers too small to handle the big, heavy B7A but by 1950, the B7A had become the standard attack aircraft on the Japanese carriers. It also equipped short-range land-based attack squadrons. The B7A remained in service until the early 1960s.

Aichi B8A Mochusai, CADS Reporting Name Frodo. The B8A was essentially a product-improved derivative of the B7A. The radial engine was replaced by turboprop and the rear gunner was eliminated, reducing the crew to a single person in a fighter-type bubble canopy. Various other weight-saving modifications were carried out, with the result that the aircraft’s payload increased dramatically, from the 2,200 pounds of the B7A to no less than 6,600 pounds. The aircraft became known in Japanese naval circles as the fleet’s heavy hitter, gaining the nickname “Adie-san” as a somewhat warped compliment to the Douglas AD-1 Skyraider. The first B8A aircraft entered service in 1952 and the type remained in service until 1966.

Kawasaki B9K Seiran, CADS Reporting Name George While the B8A was an efficient strike aircraft, the deployment of tactical nuclear weapons forced the issue of its speed. The B8A was simply too slow to deliver such weapons and a much faster aircraft was needed. Kawasaki offered a radically new aircraft to fill this role. They were developing a near-supersonic fighter for the Japanese Army that used a single Ne-45 jet engine. The design team greatly enlarged this aircraft to accommodate two Ne-45s and provide carriage for up to 4,400 pounds of warload in addition to its battery of four 30mm cannon in the nose. This aircraft appeared to be ideally suited to Japanese Navy requirements. However, mid-way through development, the Army fighter on which it was based developed severe technical problems and was withdrawn after less than a year of service. The twin-engined naval aircraft shared so much with the smaller Army plane that its development was delayed while the impending problems were corrected. On delivery, the B9K proved a great disappointment. For all its extra power, the aircraft was barely faster than the A13M. More significantly, its size made its operation from Japan’s aircraft carriers a marginal proposition. Combined with poor flying characteristics, this made the aircraft exceptionally dangerous to operate, “one a day into Ehime Bay” being a phrase commonly heard around Japanese naval bases of the time. It was no great exaggeration; of the 90 initial production B9K1 aircraft, 78 had crashed within a year of delivery. In fact, criticism of the B9K was a little misplaced, it was certainly poorly designed and used its engine power to no great advantage but the real problem was not that it was too big, it was that Japan’s aircraft carriers were too small. Japan was bumping up against the limits of its existing aircraft carrier designs and that was a problem without resolution - except by buying bigger carriers. Many of the initial problems were solved with the B9K2 and subsequent variants but the basic mismatch between existing carrier size and the larger aircraft resulting from modern requirements remained. Despite its problems, the B9K entered fleet service in 1958 and remained until the last Japanese aircraft carrier was decommissioned almost thirty years later.

Nakajima B10N Shuka, CADS Reporting Name Harry The B10N marks the changeover point in the B-classification between carrier-based attack aircraft and land-based theater-range strike. Under the strategic plans developed by Admiral Soriva between 1959 and 1965, a new strike aircraft was to be developed that combined the land-based and carrier-based strike roles. Combining these roles proved to be difficult and the aircraft that emerged was the subject of constant weight reduction exercises. Powered by two Ne-90 engines and carrying a crew of two, the B10N had a radical new solution to the problem of combining land-based and carrier-based operations. The aircraft was designed with variable geometry wings, in the forward position, they maximized lift to reduce take-off demands while swept back in the rear setting they reduced drag in order to allow the aircraft to fly at supersonic speeds. The great mystery about this design was why a carrier-based role was ever considered; the B10N was more than three times the weight of the B9K an aircraft that was already very marginal for Japan’s carriers. Operating the B10N off the existing carriers was obviously impossible. The idea that the carrier role could be disinformation can be quickly dismissed, the B10N was too compromised by the carrier requirement for this to be plausible. The obvious answer must be that a new and larger Japanese carrier was intended, the only problem being that no trace of such a carrier design has ever been found. The carrier-based role for the B10N was abandoned after the Showa Restoration Coup of 1965 and the aircraft entered service as a land-based aircraft only in 1970. It remained in service until withdrawn in 1992.

Nakajima B11N Shuka-kai, CADS Reporting Name Irving With the B10N entering service, the Nakajima team turned their attention to developing its successor. This turned out to be quite simple; with the requirement to operate carriers out of the way, they simply put back all the features that had been deleted from the B10N to save weight. The B11N had much in common with the B10N but had a longer fuselage to accommodate more fuel and payload, a bogie undercarriage in place of the single main wheels and was powered by a pair of the new Ne-75 jet engines. The result was a much more formidable aircraft that offered a truly theater-wide capability. The B11N1 entered service in 1982 and, despite slow production due to Chipan’s economic crisis, had replaced the older B10N by 1992. The B11N remains in service today.

Nakajima B12N Denko, CADS Reporting Name Jessie The B12N is the latest and most capable bomber in Japan’s theater strike forces. A long-range, supersonic, variable geometry aircraft powered by four Ne-75 jet engines, the B12N has been in production since 1988 and examples continue to join the Japanese Air Force. The current force is believed to consist of 96 aircraft, several having been lost in flying accidents.

Land-based Long Range Bombers

Historical note: This category has a confusing history. The aircraft started out as ultra-long range torpedo bombers designed to provide an added striking arm to the Japanese fleet. However, the demands of the China War saw the long-range Navy aircraft being used to strike at land targets that were out of range of the short-range Japanese Army aircraft. This lead to torpedo attack being de-emphasized in later aircraft. In 1944, the G-category was split in two with the P-group being medium-range land-based bombers tasked with attacking operational targets while the G-group reverted to naval strategic aircraft intended for attacks on shipping and naval installations. The long-range bomber group quickly became Japan’s strategic bomber force and remains so to this day. The P-group was merged with the B-category as described above.

Mitsubishi G3M Tatami, CADS Reporting Name Paul The G3M entered service with the Japanese Navy in early 1937. Its design dated from around 1934 and the aircraft bore a significant resemblance to the German Ju-86. It spent most of its career in obscurity bombing targets in China, in which role, its lack of an internal bomb bay proved a serious limitation. The G3M would doubtless be completely forgotten today except for its controversial appearance in the book “Britain Fights On” by General Sir John Hackett. In a much-criticized section of that story, Sir John had a force of G3M torpedo bombers sinking two British battleships that had been sent out to reinforce the garrison at Singapore. As many reviewers pointed out, this section clearly highlighted the general’s lack of understanding of naval warfare since it is quite inconceivable that a Navy as experienced and capable as the Royal Navy would send two capital ships out without air cover or support in the hopes of “deterring’ a much larger force of enemy ships.

Mitsubishi G4M Hamaki, CADS Reporting Name Ralph the limitations of the G3M lead to the accelerated development of its successor, the G4M. This featured an internal bomb bay and massive fuel tankage that gave it a maximum range of almost 4,000 miles. Although it was very heavily armed by the standards of its day, those fuel tanks proved to be a significant liability in service, their vulnerability making the aircraft an easy target once intercepted. The G4M started replacing the G3M in mid-1941 and, at first, the aircraft proved highly successful. However, the acquisition of more modern fighter aircraft by the Chinese Air Force caused a steep increase in casualties, especially when cannon-armed fighters, most notably the P-45 Airacobra, started to appear. As a result, the G4M was redesigned with a new wing and protected fuel tanks. The G4M continued in service until 1949 although by then it was restricted to ocean surveillance missions where fighter opposition was unlikely.

Nakajima G5N Shinzan. Experience with the G4M demonstrated that the performance limits of twin-engined aircraft were being reached and any further extension of capability could only be obtained by going to a four-engined design. In December 1939, the Nakajima company offered such a design, based on an imported DC4E airliner. The design proved over-complex and performance was far below requirements. A single prototype was built for the Japanese Army as the Ki-68 and a small number of production G5N aircraft were built for maritime reconnaissance, more to give the Japanese Navy experience in operating four-engined land-based aircraft than for any real operational need. The G5N had vanished from naval service by 1944.

Mitsubishi G6M Taizan, CADS Reporting Name Sam With the failure of the G5N, the need for a more battle-worthy replacement for the G4M picked up urgency. Mitsubishi designed the G6M to fill this need, This was primarily a further development of the G4M with its 1,500 hp Kasei radials replaced by 2,250 horsepower MK9s, the fuel tanks and crew sections protected by armor and a new, simplified wing and fuselage design. The result offered very little performance improvement over the G4M while range was severely reduced. A small number of G6M aircraft were built but the type quickly vanished from service.

Kawanishi G7K Seiku Another entry in the search to find a replacement for the G4M was the Kawanishi G7K. This took the wings and tail of the highly successful H8K flying boat and mated them to a new land plane fuselage. The resulting aircraft had a maximum speed of over 300 mph and carried the heaviest bombload of any Japanese aircraft to date, 12,800 pounds. The problem was that Kawanishi lacked the capacity to build both the G7K and the H8K in adequate numbers and this faced the Japanese Navy with an either/or situation. The H8K was considered to be the more essential of the two, especially in view of the promise offered by the new G8N and the G7K was abandoned.

Nakajima G8N Renzan CADS Reporting Name Tony Eventually, after much trying, the Japanese Navy found its long-awaited G4M replacement in the form of the Nakajima G8N. Powered by four turbocharged 2,200 horsepower Homare engines, the G8N was armed with twin 20mm cannon in nose, upper, lower and tail turrets and could carry 8,800 pounds of bombs or two torpedoes. The G8N achieved a maximum speed of 370 mph with a service ceiling of 33,500 feet and had a maximum range of 4,000 miles. The aircraft proved easy to fly and was instantly popular with its crew who also appreciated its armor plate protection for the crew positions and fuel tanks. The G8N entered service in June 1945 and immediately started replacing the G4M n the operational squadrons. In 1946, the G8N units started receiving a new weapon, a rocket-powered glider that could carry a standard Japanese naval torpedo. The idea was that the G8N would release this from outside the range of the enemy air defenses, allowing it to glide down to a launch position where it would drop its torpedo. The G8N2 carried two such weapons and trials proved it to be quite successful. The G8N remained in service throughout the 1950s with the last aircraft of the type being withdrawn in 1961. Late production aircraft ceased to have a strike role and were modified to act as anti-submarine patrol aircraft.

Mitsubishi G9M Chikara, CADS Reporting Name Eric During 1943, the Germans supplied the Japanese with sample aircraft and technical data on a number of advanced aircraft programs. It is widely assumed that these were part of an inducement to persuade the Japanese to attack Russia in the east and, hopefully, break the developing deadlock in Western Russia. The Japanese, of course, had no intention of taking on the Russians after the frightful battering Japanese units had taken in 1939 but were pleased to accept the German information anyway. One of the aircraft designs supplied to the Japanese in this manner was the Heinkel He-277. On May 25th 1944, Herman Goering made his famous speech, denying the importance of heavy bombers and vowing that such programs in Germany would receive “not one Mark, not one kilo of aluminum”. That left the He-277 as a Japanese-only program. Adapting the German design to Japanese production wasn’t easy. The He-277 was powered by four Daimler Benz DB-603 liquid cooled engines, engines that had no Japanese equivalent. As a result, it took four years to produce the first G9M prototype, the aircraft flying in late 1947, only a few weeks after The Big One. The G9M carried a maximum bombload of 8,800 pounds, could achieve 350 miles per hour and had a maximum range of 4,500 miles. Most importantly, it had a maximum ceiling of 49,200 feet, offering a possibility that the Japanese Navy could evade enemy defenses by flying over them, just as the Americans had flown over German defenses in their B-36s. The G9M remained a highly complex and unreliable aircraft and its production run was limited as a result. Its main contributions were that it was one of the threats driving the development of the NORAD American air defense system and it taught the Japanese aircraft industry a lot about high-flying aircraft. The G9M was withdrawn from service from 1954 onwards as the G10N arrived to replace it.

Nakajima G10N Fugaku, CADS Reporting Name Frank Flushed with the success of the G8N, Nakajima were already investigating the possibility of a successor when the data from the procurement of the Heinkel He-274 and He-277 was secured. They grasped the importance immediately; this information offered the possibility of building a truly trans-Pacific bomber. The original design was essentially a pressurized version of the G8N, powered by four Nakajima Ha-505 engines rated at 4,100 horsepower each. It quickly became apparent that this approach was far too conservative and much more could be achieved. Accordingly, a new aircraft was designed, using six of the same engines combined with a beautifully-streamlined airframe. In this, the Japanese had some advantages over the Convair team that had produced the B-36. They were running six years later than the Americans and could exploit the advances in technology that had taken place since 1940 and, after The Big One, they had the example of the B-36 and could build on that. The results were obvious when the G10N were flown. The new bomber cruised at 49,200 feet and could achieve a range of 12,000 miles carrying an 11,000 pound bombload. Its maximum load was 44,000 pounds. Most significantly, the G10N had a maximum speed of 484 miles per hour at 32,000 feet and was about 20mph faster than the B-36 at 49,000. The remarkable thing was that this performance was achieved without the need for jet boost.

The first prototype G10N flew in 1948 amid conditions of stringent security comparable with those surrounding the construction of the Yamato class battleships. Despite this (and perhaps an early mark of the slow decline within Japan), US intelligence started picking up rumors of the development of the big bomber. Nothing concrete was available but it was apparent that the Japanese were building a very large trans-Pacific bomber. Testing this large and complex program took time but was eventually completed and the G10N entered service in 1951. A year later, Japan initiated its first nuclear weapon. NORAD’s nightmare had become reality; another nation now had the capability to follow America’s example and fly over any existing defense and drop its bombs on enemy cities. Only, now the “enemy cities” were American. Despite four years of development since the first Red Sun exercise in 1948, the United States still had no effective means of stopping a nuclear attack. Land values in California went into free-fall.

The most immediate effect of the arrival of the nuclear-armed G10N was an eruption in American politics. An obscure Senator, Joe McCarthy, started a series of hearings into who had allowed Japan “to steal the bomb” and “allowed a bomber gap to develop”. Although the G10N had a performance edge over the B-36, the dozen or so G10Ns available in January 1953 could hardly be compared with American fleet of more than two thousand B-36s. McCarthy’s hearings were more noted for their bile than their accuracy and were widely condemned. In later years it was realized that the harm they had done was greatly overstated but they still remain an embarrassing note in American history.

The window of vulnerability closed during 1954 as the F94C Starfire and F86D Sabredog arrived and started to equip interceptor squadrons along the West Coast while Ajax missile batteries started to appear around American cities. The Japanese responded by deploying the G10N3, a version of the G10N that could fire Ohka long-range stand-off missiles. By 1955, an attack pattern had been set where Ohkas fired from submarines were assigned targets in the first tier of states along the Pacific coast while Ohkas fired from G10Ns, longer ranged due to the altitude and speed of their launch, attacked the next tier of states inland. The G10N remained in service until 1959 when the remaining members of the fleet were converted into G11Ns.

Nakajima G11N Fugaku-kai, CADS Reporting Name Frank This aircraft was a simple modification of the original G10N, replacing the 4,100 hp radial engines with 6,600 ehp NT-30 turboprops. The glazed nose was replaced by a solid nose containing a bomb-navigation radar. Primary armament was one of the ever-faster, ever longer-ranged Ohka piloted long-range cruise missiles. Approximately 200 G11Ns were built and all the earlier G10Ns were converted to the new standard. The G11N entered service in 1958 and remained until 1978.

Nakajima G12N Kirigamine, CADS Reporting Name Geoff The G12N was a major redesign of the basic G11N concept. The six NT-30 turboprops were replaced by four NT-70 turboprops rated at 13,300 ehp each. These were placed unusually outboard, allowing space under the inner wing panels for an Ohka missile, enabling each G12N to carry two missiles with the possibility of lifting a third under the belly for shorter-range missions. The wing roots were thickened to include a tunnel that would allow the pilots to climb through the wing and down the thick wing pylon in order to man their Ohkas. The G12N had its wings and tail moderately swept and the aircraft was capable of 550mph with a service ceiling of 52,500 feet. The G12N entered service in 1971 and the last examples were withdrawn in 1995.

Nakajima G13N Kirigamine-kai, CADS Reporting Name Geoff Superficially identical to the G12N, the G13N can be distinguished by its reprofiled cockpit and a two-meter extension to the fuselage ahead of the wing. In reality, it is quite a different aircraft from the G12N. It entered production in 1985 and remains in service today.


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