The Yokosuka Type 91 Intermediate Trainer was judged to be too close in performance to contemporary service aircraft, and was thus rejected for production. After further development an improved version did enter service as the Yokosuka K5Y Type 93 Intermediate Trainer 'Willow'.
By 1930 a gulf had opened up between the Japanese Navy's primary trainers, which tended to have 100hp engines, and their operational aircraft, with 500hp or more. In order to fill that gap the Navy asked Yokosuka to produce a 300hp intermediate trainer that would fall between the two in performance, and allow for initial training with armed aircraft.
Jiro Saha and Tamefumi Suzuki designed the aircraft. They produced a neat single bay biplane with N struts, cowled main wheels, powered by a radial engine with a ring cowling. The new aircraft used a welded steel tube framework for the fuselage and wooden framework for the wings, both fabric covered. It could carry two 66lb bombs and was armed with a fixed forward firing machine gun.
The first prototype was complete in April 1931, and was quickly given an official designation as the Type 91 Intermediate Trainer. However further tests revealed that the designers had produced rather too effective an aircraft, with similar aerobatic and speed characteristics to the combat aircraft then in use, and poor stability. It might have made a promising fighter, but it was a poor intermediate trainer. The project was cancelled after only two prototypes had been produced. However the design was used as the basis of the more successful Yokosuka K5Y Type 93 Intermediate Trainer 'Willow'.
Engine: Gasuden Tempu 11 nine-cylinder air-cooled radial engine
Span: 36ft 5in
Length: 25ft 10.5in
Height: 10ft 10.5in
Empty weight: 2,204lb
Loaded weight: 3,306lb
Max speed: 127mph
Climb Rate: 15min 10sec to 9,843ft
Armament: One fixed forward 7.7mm machine gun
Bomb load: Two 66lb bombs