Kawanishi H6K. The Kawanishi H6K was an Imperial Japanese Navy flying boat produced by the Kawanishi Aircraft Company and used during World War II for maritime patrol duties. The Allied reporting name for the type was Mavis; the Navy designation was .
Developed in the 1930s, it was used for reconnaissance, transport, bombing, naval warfare, and executive transport by the Imperial Japanese Navy. The national airline also used it as commercial airliner. The British mistakenly identified this aircraft as the Kawanishi Navy 97 Mavis.

Design and development

The aircraft was designed in response to a Navy requirement of 1934 for a long-range flying boat and incorporated knowledge gleaned by a Kawanishi team that visited the Short Brothers factory in the UK, at that time one of the world's leading producers of flying boats, and from building the Kawanishi H3K, a license-built, enlarged version of the Short Rangoon. The "Type S", as Kawanishi called it, was a large, four-engined monoplane with twin tails, and a hull suspended beneath the parasol wing by a network of struts. Three prototypes were constructed, each one making gradual refinements to the machine's handling both in the water and in the air, and finally fitting more powerful engines. The first of these flew on 14 July 1936 and was originally designated "Navy Type 97 Flying Boat", later H6K. Eventually, 217 were built.

Production & engines 
Four prototypes were produced leading to the production version, with ten H6K2 built, then 124 H6K4 were produced which had better fuel capacity. All H6K were powered by 4 radial piston engines of different types. Some aircraft were upgraded with the 1000 hp Kinsei 46, and the H6K5 had the 1300 hp Kinsei 51/53.

The H6K prototype was powered by four 9-cylinder Nakajima Hikari 2 with 840 hp. 

Additionally production:

 Sixteen H6K2-L unarmed transports
 Two (2) H6K4-L VIP transports
 Twenty (20) H6K4-L unarmed transports with the Kinsei 46 engines
 Thirty-six H6K5s with Kinsei 51/53
Sixteen (16) aircraft were civilian air transports operated by Dai-Nippon Airways (the Imperial Japanese National airline), with on board toilet, galley, and room for 18 passengers. They had civil registration and were used for mail and passenger service to the Pacific. 

Combat H6K were armed with various combinations of  Type 92 machine guns, and it could also carry two torpedoes or 1000kg of bombs.

Operational history

H6Ks were deployed from 1938 onwards, first seeing service in the Sino-Japanese War and were in widespread use when the Pacific War began in December 1941. At the start of the war, four Kōkūtai (naval air groups) operated a total of 66 H6K4s. Also, sixteen were used by the Imperial Japanese airline for mail and passenger service to the Pacific.

On 12 December 1941, during the Battle of Wake Island, an H6K bombed Wake island, but it was shot down by an F4F Wildcat.

On 15 February 1942, a P-40 Warhawk intercepted an H6K, about 190 km west of Darwin, Australia, which had attacked Allied shipping; both the P-40 and H6K were shot down.

The type had some success over Southeast Asia and the Southwest Pacific. H6Ks had excellent endurance, flying up to 24-hour patrols, and were often used for long-range reconnaissance and bombing missions. From bases in the Dutch East Indies, they could fly over a large portion of Australia.

However, the H6K became vulnerable to a newer generation of more heavily armed and faster fighter aircraft. In front-line service, it was replaced by the Kawanishi H8K. It continued in service throughout the war but in areas where the risk of interception was low.

Variants

 H6K1
Evaluation prototypes with four Nakajima Hikari 2 engines, four built.
 H6K1 (navy flying boat Type 97 Model 1)
Prototypes with 746 kW (1,000 hp) Mitsubishi Kinsei 43 engines, three converted from the original H6K1 prototypes
 H6K2 Model 11
First production model. Includes two H6K2-L officer transport modification, 10 built.
 H6K2-L (navy transport flying boat Type 97)
Unarmed transport version of H6K2 powered by Mitsubishi Kinsei 43 engines, 16 built
 H6K3 Model 21
Modified transport version of H6K2 for VIPs and high-ranking officers, 2 built
 H6K4 Model 22
Major production version, modified H6K2 with revised weapons, some with 694 kW (930 hp) Mitsubishi Kinsei 46 engines. Fuel capacity increased from 7,764 L (1,708 Imp gal) to 13,410 L (2,950 Imp gal). Includes two H6K4-L transport versions, 100 to 127 (if other numbers are all correct) built.
 H6K4-L
Transport version of H6K4, similar to H6K2-L, but with Mitsubishi Kinsei 46 engines, 20 built and another two converted from the H6K4
 H6K5 Model 23
Fitted with 969 kW (1,300 hp) Mitsubishi Kinsei 51 or 53 engines and new upper turret replacing the open position, 36 built

Operators

 Imperial Japanese Navy Air Service
 Imperial Japanese Airways
 Used on the routes Yokohama-Saipan-Koror (Palau)-Timor, Saigon-Bangkok and Saipan-Truk-Ponape-Jaluit

Air Service Volunteer Corps - A single H6K5 flying boat was restored to flight by British and Indonesian forces during the Indonesian War of Independence.

Specifications (H6K4 Model 22)

See also

Notes

Bibliography
 Doubilet, David. "The Flying Boat". Sport Diver Magazine. Volume 15, Number 8, September 2007.
  (new edition 1987 by Putnam Aeronautical Books, .)
 
 
 
 "Pentagon Over The Islands...The Thirty Year History of Indonesian Military Aviation". Air Enthusiast Quarterly. No. 2, n.d. pp. 154–162.
 Richards, M.C. "Kawanishi 4-Motor Flying-Boats (H6K 'Mavis' and H8K 'Emily')". Aircraft in Profile Volume 11. Windsor, Berkshire, UK: Profile Publications Ltd., 1972.
 Van der Klaauw, Bart. Water- en Transportvliegtuigen Wereldoorlog II (in Dutch). Alkmaar, the Netherlands: Uitgeverij de Alk. .

External links

 Duel between an HK6 and 2 B-17s

H6K
H6K, Kawanishi
Flying boats
Four-engined tractor aircraft
Parasol-wing aircraft
Aircraft first flown in 1936
Four-engined piston aircraft