00:21These were the biggest Japanese planes when they appeared, and a showcase of the very
00:25best in the country's flying boat building experience.
00:28But as time passed during World War II, their shortcomings and vulnerabilities became more
00:33and more apparent.
00:34Still they served until the end of the war in various roles.
00:38They were the Kavanishi H-6K flying boats.
00:42So let's see the history of these aircraft today.
00:50These big flying boats were used by the Japanese Navy on the Pacific during the first part of
00:55the war, but when they encountered the newer heavily armed American fighters and patrol
00:59bombers, they proved to be an easy target for the Allied gunners.
01:03The American crews were very surprised to see how these giant planes burst into flames after
01:08just a few hits, and plunged into the ocean.
01:11As it turned out, chasing performance and long range made these flying boats too fragile for
01:16heavy combat use.
01:18So let's go back in time and see how and why they were created this way.
01:26Their history actually started more than a decade before World War II, when the Kavanishi
01:30company started to build its expertise with flying boats.
01:34Before World War II the planned Japanese expansion on the Pacific raised the question of long range
01:39reconnaissance and bomber aircraft as a requirement to fight a war on the vast ocean.
01:44Since the land-based aircraft would have needed airfields built on almost every island, the
01:48flying boats were a logical choice for these roles.
01:52The Kavanishi Aircraft Company built several airplanes for the military in the 1920s, and
01:57they were tasked in 1929 to acquire a new advanced flying boat.
02:02This led to Kavanishi's team visiting the United Kingdom, looking for a suitable aircraft at the
02:07Short Brothers Company.
02:08Their visit led to the purchase of the right to build a modified version of the Short Rangoon
02:13flying boat under license.
02:15This type now built in Japan became the Kavanishi H3K, and was accepted into service in 1932.
02:23But in the same year lots of changes happened in the Navy administration, and a new leadership
02:28set out to raise the quality of the Navy aircraft, and also replaced the license-built planes
02:33with pure Japanese designs.
02:35As the most experienced Japanese company building flying boats, Kavanishi received specifications
02:40for a new experimental flying boat in 1933.
02:44They worked out two designs for these requirements.
02:47The four-engined Type-Q, and the three-engined Type-R flying boats.
02:52But after the Navy examination, none of these designs advanced further than scaled model testing.
02:58In the next year, however, the Navy issued exclusive requirements to Kavanishi for the so-called
03:03X-9 project, a big four-engined monoplane flying boat.
03:08As it usually happened with Japanese requirements of the time, these new specifications were extremely
03:13ambitious.
03:15The new design had to be able to outperform all the Western designs in production at the time.
03:19Or to put it simply, it had to be the best of the world.
03:23They asked for at least 220 km an hour cruise speed, and more than 4,500 km range, with powerful
03:31armament and ability to carry torpedoes and bombs.
03:36Using the experience they gathered with flying boats, the Kavanishi company presented their
03:41new so-called Type-S design to these 1934 requirements.
03:45The new aircraft, designed under the lead of Yoshio Hachiguchi and Shizuoki Kohara, was
03:50a big monoplane, with a twin tail, and it was powered by four Nakajima Hikari II air-cooled
03:56radial engines.
03:57To achieve the required speed and range, the design featured the largest wingspan on seaplanes
04:02up to that date, with 40 meters.
04:04And it was not just the biggest Japanese flying boat, but the biggest Japanese aircraft of its
04:08town.
04:09On the other hand, because the designers had to balance between the extremely ambitious
04:13requirements and the relatively underpowered engines available, similarly to many other
04:18contemporary Japanese aircraft, it completely lacked armor plating and fuel tank protection.
04:25The new design in its elegant lines was very reminiscent to the Dornier DO-18 and DO-24 types.
04:31If you're interested in the history of those German flying boats, check out my earlier video
04:36covering those types.
04:39The first prototype of the Kavanishi design was finished in summer 1936 and made its maiden
04:44flight on 14th of July without any big problems, and only slight modifications to the hull were
04:49required for better handling of water.
04:52After the initial test flights, the prototype was handed over to the Navy for evaluation at the
04:57end of the month.
04:58Though the type fulfilled the Navy's requirements, they found it slightly underpowered with the
05:03original 840 horsepower engines.
05:07The second and third prototypes were delivered during 1937 and the fourth one in 1938.
05:14During the testing, several small modifications were made to the type, mainly on the control surfaces.
05:19And to fix the lack of power, during 1937 the original engines were replaced with 1000
05:25horsepower Mitsubishi Kinsei 43 types, raising the total power from 3360 horsepower to 4000.
05:34The type with the new modifications was accepted by the Navy in January 1938 as H-6K-1 Navy Type
05:4197
05:42Flying Boat Model 1, and it was ordered into full production with a contract for 200 units.
05:51The armament for the type was planned to be three 7.7 mm machine guns, one in the nose, one
05:57in the tail,
05:57and one in the dorsal turret, and the plane had the capability to carry either two torpedoes
06:02or 1000 kilogram bombs under the wings.
06:06But as with many other Japanese military planes, the designers' efforts to comply with the requirements
06:11resulted in a very vulnerable design, hurting the performance of these planes on the long run,
06:16even though many modifications were made to the type during production.
06:20So let's take a look at those next.
06:30The initial prototypes were the H-6K-1 variants tested by the Navy.
06:36The first 10 production models, featuring armament and the stronger 1000 horsepower engines,
06:42received the designation H-6K-2, and two of these models were modified to personal transport,
06:48as H-6K-3 models.
06:51During production, further modifications were applied to the type.
06:55The fuel capacity was increased, the door satiret was deleted, and two waste gunner positions were added
07:01instead, and the machine gun in the tail was replaced with a 20 mm cannon.
07:05These updated variants received the H-6K-4 designation, and were the most numerous variant of the type,
07:12with more than 120 units built.
07:16In 1942, a further upgraded variant of the type, the H-6K-5 appeared,
07:22which featured new 1300 horsepower Kinsale 53 engines,
07:26and a machine gun turret was installed behind the cockpit.
07:3036 units were built from this variant.
07:35There were also transport variants, built without armament.
07:3814 units of the H-6K-2-L unarmed transport variants were made,
07:43and a further 20 units based on the H-6K-4 were built without armament,
07:47under the designation H-6K-4-L.
07:52In total, between 1936 and 1943,
07:55250 units were built, including the prototypes.
08:06The Kavanishi H-6K-4 model was 25.63 meters long, with a wingspan of 40 meters.
08:14It had an empty weight of 11.707 kg, and a maximum take-off weight of 21.500 kg.
08:23The plane was powered by four Mitsubishi Kinsale 43 air-cooled radial engines,
08:28each of them producing 1.000 horsepower.
08:32With these engines, the big flying boat was able to reach a top speed of 340 km an hour,
08:37and a cruise speed of 222 km an hour.
08:42It had a service ceiling of 9.600 meters, and a combat range of 4.800 kilometers,
08:48with a ferry range of more than 6.000 kilometers.
08:54The plane's defensive armament consisted of three 7.7 mm machine guns,
08:59one in the nose and two in the waist gunner positions, and a 20 mm cannon in the tail.
09:04The secondary armament consisted of either two torpedoes or 1.000 kg of bombs.
09:21The Kavanishi H-6K entered service in 1938, and their first combat actions took place in the
09:28Sino-Japanese War. When the war on the Pacific broke out, 66 of these flying boats were in service
09:34with the Japanese Navy, and they proved to be very useful with their more than 4.000 kilometers range
09:39for conducting long-range reconnaissance or attack missions.
09:42They participated in the attacks against Baker Island and Wake Island,
09:46they also bombed a Dutch seaplane base at Heron, and they also attacked Rabaul.
09:51But very soon these combat missions highlighted the weakness of the aircraft.
09:56Though their excellent range was very useful in the reconnaissance role,
09:59they were vulnerable when attacking enemy installations.
10:02The unprotected, big and slow aircraft was an easy target for ground fire and allied fighters.
10:09Soon the type was withdrawn from direct combat missions, and they were assigned to reconnaissance roles.
10:14By the end of 1941, a new, more advanced flying boat, the Kavanishi H-8K was already in the works,
10:21which featured more protection and defensive armament.
10:24While preparations were made for the production of the new type, the H-6K was further improved with the
10:30H-6K-5 variant, which thanks to its 1,300 horsepower engines now could reach a top speed of 390
10:37kilometers an hour.
10:39But only 36 were built from this variant, as in 1942 the production lines were shifted to the new H
10:45-8K model.
10:48In the later phases of the war, the H-6K flew less and less reconnaissance missions,
10:53as they were slowly replaced by newer types, and their main use was to fly cargo missions.
10:59But despite the more advanced H-8K Emilie entering service,
11:03the old Mavis served all the way to the end of the war, though only 12 of them remained in
11:08service by that time.
11:11Though the Kavanishi H-6K quickly showed its weakness during World War II,
11:15but it was an excellent showcase of the pre-war Japanese plane building expertise.
11:20And it was the biggest aircraft in Japan when it appeared.
11:26Hope you guys enjoyed this video. Please leave a like, subscribe to my channel,
11:29and in the comments let me know if there's any interesting events or vehicles you'd like to see.
