Being an island superpower at the time of World War 2 (1939-1945), the Empire of Japan relied heavily on the capabilities of its flying boat fleet. As the reach of the Empire grew to threaten the American West coast, the Australian mainland, and many parts of Southeast Asia, this fleet of aircraft became evermore critical to the Japanese scope of operations in the Theater.
By this time in history, the Kawanishi concern was an established flying-boat-maker and claimed some of the more successful flying boat designs of the war - the H6K "Mavis" and the H8K "Emily" being two such examples. Before the close of the war in August of 1945, it tried its hand at what would have become the largest flying boat in Imperial Japanese Navy (IJN) service - the oversized H1K "Soku" ("Blue Sky").
Flying boats have always offered several key inherent strategic advantages during war, namely operational range and no restriction on airstrip length. Able to take-off from a water source, the aircraft type could be operated nearly anywhere that the IJN was committed to during the far-reaching conflict. For the new design, the aircraft would be of considerable size in an effort to haul as much war-making goods from Point A to Point B as possible - helping to reinforce Army positions across the Pacific and turn the tide of active battles elsewhere.
One key restriction placed on engineers was in extensive reliance on wood for metal had become a precious commodity in wartime, resource-strapped Japan. Designers returned with a dimensionally large flying boat showcasing a high-wing monoplane form that held outrigger pontoon legs (non-retractable). The fuselage was slab-sided with a deep profile, the flight deck (notable for its range of windows for optimal viewing out-of-the-cockpit) seated atop the frontal section and ahead of the wing mainplanes. The empennage was conventional, tapered to meet the base of the single vertical fin. Horizontal planes were feature at the base of the fin itself. As with other flying boats, the aircraft was given a boat-like hull for water landings and take-offs so no complicated wheeled undercarriage was required. The crew complement numbered five and local defense was to come from 3 x 13mm Type 2 machine guns.
Selected propulsion power was to be generated from 4 x Mitsubishi MK4Q "Kasei 22" (Ha-32-22) radial piston engines developing 1,850 horsepower each and driving four-bladed propeller units. These were seated (as pairs) along the wing leading edges in the usual way - given proper clearance from the spray of the salty ocean.
Internally, the aircraft would feature a smaller upper deck for the flight crew and a lower deck representing the cargo hold. A split-nose assembly gave the needed access to the deep hold which could ferry several military vehicles, some 80 combat-ready troopers, wounded (MEDEVAC role), or comparable cargo loads as needed.
For Kawanishi, the aircraft was designated as the "KX-8" and IJN authorities approved the design direction of the large, much-needed aircraft as the "H11K" - the initial production model to become the "H11K1". A full-scale mockup was ordered and this began construction on Shikoku.
Due to the worsening war situation for Japan heading in 1945, the H11K's mockup was not to be completed until later that spring and Kawanishi became evermore committed to fighter production for the ultimate defense of the Japanese mainland. The final blow for the giant flying boat arrived on April 1st, 1945 as Allied bombs rained down on the Kawanishi facility destroying the nearly-completed mockup. Since there was no time to resurrect the design and interceptors were in dire need, all work was ended on the H11K.
Projected performance for the flying boat included a maximum speed of 292 miles per hour, a cruise speed of 230mph, and an operational range out to 2,415 miles.