The Watanabe K8W1 Experimental 12-Shi Primary Seaplane Trainer was designed to replace the Yokosuka K4Y1 Type 90 Seaplane Trainer, but lost out to a Kawanishi design.
In April 1937 the Navy issued a specification for a 12-Shi Primary Seaplane Trainer and asked Nippi, Watanabe and Kawanishi to produce designs. The new aircraft was to be powered by a 130hp Jimpu engine, and had to be a twin-float biplane.
Watanabe produced a single-bay biplane, with a metal fuselage structure, wooden wing structure and a fabric covering. The crew of two sat in open cockpits. All three of the rival designs were very similar, and indeed weren't that different to the original Type 90.
Kawanishi won the contest and their design entered production as the Kawanishi K8K1 Type 0 Primary Seaplane Trainer. However by the time the contest was over the Japanese Navy had started to use the Yokosuka K5Y Type 93 Intermediate Seaplane Trainer as a primary trainer. In addition the new Kawanishi design wasn't much of an improvement over the Type 90, and so only fifteen were built.
Engine: Gasuden Jimpu 2 seven-cylinder air-cooled radial engine
Span: 32ft 9 1/2in
Length: 28ft 6 1/2in
Empty weight: 1,653lb
Loaded weight: 2,237lb
Climb Rate: 20min to 9,843ft
Service ceiling: 11,482ft
Endurance: 4 hours