Introduction and Development
Introduction and Development
The Kawanishi H8K 'Emily' was the fastest and most heavily armed flying boat to enter service in significant numbers during the Second World War, and was considered by Allied pilots to be the hardest Japanese aircraft to shoot down.
Work on the H8K began in 1938, in response to a 13-Shi specification for a large flying boat to replace the Kawanishi H6K, which had just entered service. The new aircraft was to have a top speed of 276mph, a cruising speed of 207mph and a normal range of 5,180 miles. Kawanishi responded with a high-wing monoplane with a large hull, a single vertical tail, and a superficial resemblance to the Short Sunderland, although the H8K was larger and would prove to have much better performance. The aircraft had eight small unprotected fuel tanks in the wings and six larger partially self-sealing tanks in the lower hull. These tanks were placed over fuel-proof bilges, and any split fuel could be pumped into other tanks. The aircraft could carry 3,249 gallons of fuel, giving it a range of over 4,400 miles, down on the specification but still very impressive. Unusually for Japanese aircraft of the period, the H8K was heavily armoured and would prove to be a sturdy aircraft.
The prototype was completed on 31 December 1940. Its maiden flight came in the following month and was somewhat disappointing. The aircraft was good in the air, but was unstable during high-speed taxing and during take-off. These problems were solved by increasing the depth of the hull by 1ft 7 11/16in and modifying the shape of the hull bottom. Towards the end of 1941 the modified aircraft was approved for production as the H8K1 Navy Type 2 Flying Boat Model 11.
Although the H8K was designed as a long range maritime patrol aircraft, its first combat mission was actually a bombing raid on Hawaii. This was a long range attack launched by two aircraft based in the Marshall Islands on 4-5 March 1942. They refuelled from a submarine at a site in the French Frigate Shoals, then made a disappointing raid on Oahu, where heavy cloud prevented them from bombing accurately. A second raid at the time of the battle of Midway had to be cancelled because the American fleet was using French Frigate Shoals.
For the rest of the war the H8K served as a long range reconnaissance aircraft, a role in which it excelled. Its high speed allowed it to escape from many Allied fighters and its armour and self-sealing fuel tanks meant it could survive an attack.
The H8K2 was the best flying boat to serve with any side during the Second World War. It was over 100mph faster than the Consolidated Catalina, although carried about the same payload. It was slightly larger than the Short Sunderland, which it resembled physically, but had over 2,400hp more power, was 70mph faster and much heavier armed. Again the payload was about the same although the Sunderland could carry more bombs. However both of this Allied aircraft were built in rather larger numbers than the H8K. Around 750 Sunderlands were built, while over 3,200 Catalinas were completed. In contrast only 167 H8Ks were built.
H8K1 Navy Type 2 Flying Boat Model 11
The first production version of the H8K differed slightly from the prototype. It was powered by 1,530 Mitsubishi Kasei 11 or 12 radial engines, as on the prototype, but had a modified vertical tail and reduced defensive firepower, with some of the 20mm cannon replaced with machine guns. Even so it was still left with one 20mm cannon in each of the dorsal and tail turrets, and flexibly mounted 7.7mm machine guns. It could carry two 1,764lb torpedoes, eight 551lb bombs or sixteen 132lb bombs or depth charges, all held under the wings. Only sixteen were built before production switched to the H8K2.
H8K2 Navy Type 2 Flying Boat Model 12
The H8K2 was powered by four 1,850 Mitsubishi MK4Q Kasei 22 radial engines, with water injection to increase power. Speed went up by 21mph, and four minutes were cut off the time to 16,405ft. The extra engine power also increased the aircraft's maximum operating weight, allowing the armament to be increased to include 20mm cannon in nose, dorsal and tail and port and starboard beam positions, as well as 7.7mm machine guns in a ventral position, port and starboard fuselage sides and the cockpit hatches, for a total of ten guns. This made the H8K2 the most heavily armed flying boat in service with any side during the Second World War. Allied airmen considered it to be the hardest Japanese aircraft to shoot down. Late production aircraft were also equipped with ASV radar (Air to Surface Vessel). A total of 112 H8K2s were built.
H8K3 Navy Type 2 Flying Boat Model 22
The designation H8K3 was given to two aircraft given retractable stablizing floats in an attempt to improve performance. These aircraft also had sliding side windows instead of blisters. The two aircraft were produced during 1944.
H8K4 Navy Type 2 Flying Boat Model 23
This designation was given to the two H8K3s after they were given four 1,825hp Mitsubishi MK4T-B Kasei 25b radial engines during 1945. Neither the H8K3 nor H8K4 entered production.
H8K2-L Navy Type 2 Transport Flying Boat Seiku (Clear Sky).
The H8K2-L was a transport version of the H8K2. It could carry 29 passengers or 64 troops on two decks. Most of the guns were removed, leaving one 20mm cannon and one 7.7mm machine gun. Thirty six were produced between 1943 and 1945, and were used by Naval Transport Units.
H8K4-L Model 33
This was the designation given to a transport version of the H8K4, using the Kasei 25b radial engines. None were built.
Engine: Four Mitsubishi MK4Q Kasei 22 fourteen-cylinder air-cooled radial engines.
Power (each): 1,850hp at take off, 1,680hp at 6,890ft, 1,540hp at 18,045ft
Wing span: 125 ft 8 1/16in
Length: 92ft 3 15/16in
Height: 30ft 1/4in
Empty Weight: 40,521lb
Loaded Weight: 54,013lb
Maximum Weight: 71,650lb
Max Speed: 290mph at 16,405ft
Cruising Speed: 184mph at 13,125ft
Service Ceiling: 29,035ft
Range: 4,445 miles
Armament: Five 20mm cannon and five 7.7mm machine guns
Bomb-load: Two 1,764lb torpedoes, eight 551lb bombs or sixteen 132lb bombs or depth charges