Owing much to current American and French flying-boat design of the mid 19303, the large four-engine Kawanishi Type 97 parasol monoplane flying boat, which had first flown in July 1936, was Japan's only in-service long-range reconnaissance flying-boat when that nation went to war in December 1941, much effort having been dissipated in transport conversions and deliveries to Japan's commercial operators in the Pacific. The H6K1 initial military version entered limited service with the
Imperial Japanese Navy in 1938, and was followed by 10 H6K2 flying-boats.
The first major production version, the H6K4 was powered by four Mitsubishsi Kinsei 43 radiais and armed with four 7.7-mm (0.303-m) machine-guns in bow and midships positions and a 20- mm cannon in a tail turret, and was capable of carrying two 800-kg (1,764-Ib) bombs or torpedoes, a total of 66 being in service at the time of Pearl Harbor; later aircraft were powered by Kinsei 46 engines. These 'boats were widely employed, although the initial heavy defeats inflicted on the Allies in the Pacific rendered maritime reconnaissance duties subordinate to the need for air transportation of Japanese troops during the swift conquests in the East Indies and elsewhere.
A number of aircraft, designated H6K4-L, were therefore converted for transport duties and were each able to accommodate about 18 fully-armed troops; lacking armour and self-sealing fuel tanks, however, they were extremely vulnerable to fighter attacks and, after a number had been shot down, a new version entered production as the H6K5 in August 1942; by that time the maritime reconnaissance version had been given the reporting codename 'Mavis' by the Allies, the transport derivative being named Tillie'. Powered by either Kinsei 51 or 53 radiais, the H6K5 was intended to eliminate the shortcomings of the earlier versions, but although the open bow gun position was replaced by a single-gun turret immediately aft of the pilot's cockpit, the overall armament was not increased. Only 36 H6K5s were completed by 1943, when production gave place to the greatly superior H8K, H6Ks served with the 8th, 14th, 801st, Toko and Yokohama Kokutais, and some of the H6K5s were employed as naval staff transports throughout the Pacific in 1943.
Eighteen aircraft served on the quasicommercial courier services in South East Asia, a number of them being destroyed by Allied aircraft both in the air and at their moorings.
Type: nine-crew maritime reconnaissance flying-boat
Powerplant: four 1,300-hp (970-kW) Mitsubishi Kinsei 53 14-cylmder aircooled radiais
Performance: maximum speed 385 km/h (239 mph) at 6000 m (19,685 ft); climb to 5000 m (16,405 ft) in 13 minutes 24 seconds; service ceiling 9600 m (31,495 ft); maximum range 6775km(4,210miles)
Weights: empty 12380 kg (27,293 lb); maximum take-off 23000 kg (50,705 lb)
Dimensions: span 40.00 m (131 ft 23/4 in); length 25.63 m (84 ft 0% in); height 6,27 m (20 ft 6% in); wing area 170.00m2 (1,829.86 sq ft)
Armament: four 7.7-mm (0.303-in) machine-guns in front and midships dorsal positions and two beam blisters, and one 20-mm cannon in tail, plus a bombload of up to 2000 kg (4,409 lb) or two 800-kcr ( 1,764-lb) torpedoes