Design and development
Drawing on the company's H11K and K-60 designs, the K-200 was to use six turbojets. The suggestion that the K-200 was intended to replace other long-range heavy flying boats in Imperial Japanese Navy (IJN) service and that the K-200 was also proposed as the delivery platform to carry a Japanese nuclear weapon to the United States are not supported with evidence.
The IJN may have asked Kawanishi to consider a turbojet powered flying boat or it may have been a company initiative. Support for the latter comes from the IJN's request for the Kawanishi H11K Soku and the K-60, both large flying boats, and thus a suggestion may have been made.
For such a large flying boat, the K-200 likely would have been powered by the Ne-330 turbojet. This was the last turbojet design in progress before the war ended and which had the highest thrust rating at 1,300 kg of thrust. However, the Ne-330 consumed 1.95 kg of fuel per kg of thrust and six Ne-330 engines would have resulted in the K-200 needing to devote a large portion of its weight for fuel. A consequence of this would be a rather short operational range, inferior to the main IJN flying boat, the Kawanishi H8K "Emily", even through the speed would have been faster. This shorter range would have made the K-200 a poor candidate as an aircraft capable of reaching the U.S. to deliver an atomic weapon.
The engines were mounted on top of the wing, three per wing. This position would minimize water ingestion by the engines.
It is likely that the K-200 sported a weapon fit similar to the H8K. This would have consisted of a Type 99 20mm cannon in a tail turret and in a turret on the top of the fuselage, forward of the wings. Blisters on the forward port sides of the hull would have carried either the Type 99 or the Type 92 7.7mm machine-gun. Another cannon was located in the nose. The K-200 may have also been capable of carrying torpedoes, depth charges, or bombs.
As a note, one such illustration of the K-200 looks much like the Russian Beriev R-1.
The war ended before plans for the K-200 could be completed.
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