Designed by the naval Air Technical Arsenal at Yokosuka, and developed as a collaboration between the Yokosuka Arsenal and Kawanishi, the Yokosuka K5Y1 was first flown in prototype form during December 1933. Early flight tests and service trials proceeded without any serious problems, the type entering production in January 1934 under the official designation Navy Type 93 Intermediate Trainer. Most extensively built of all Japanese navy training aircraft, 5,770 K5Ys were built by Fuji (896), Hitachi (1,393), Kawanishi (60), Mitsubishi (60), Nakajima (24), Nippon (2,733), Watanabe (556) and the 1st Naval Air Arsenal at Kasumigaura (75), their production extending from 1934 until the end of the Pacific war. The initial K5Y1 had wheel -landing gear, but alternative twin-float versions were available as the K5Y2 with a Hitachi Amakaze 11 engine or K5Y3 with a 515-hp (384-kW) Hitachi Amakaze 21 radial engine. Projected but not built were two land-based versions, the K5Y4 with a 480-hp (358-kW) Amakaze 21A engine, and K5Y5 with the 515-hp (384-kW) Amakaze 15.
An unequal-span biplane with fixed tailskid landing gear as standard, all were powered by radial engines and had two separate open cockpits in tandem. Allocated the Allied codename 'Willow', these trainers saw extensive use throughout the whole of their production period.
Type: two-seat land-based intermediate trainer
Powerplant: one 340-hp (254-kW) Hitachi Amakaze 11 9-cyIinder radial piston engine
Performance: maximum speed 132 mph (212 km/h) at sea level; cruising speed 86 mph (138 km/h) at 3,280 ft (1000 m); service ceiling 18,700 ft (5700 m); range 634 miles (1020 km)
Weights: empty 2,205 lb (1000 kg); maximum take-off 3,307 lb (1500 kg)
Dimensions: span 36 ft 1in (11.00 m); length 26 ft 5 in (8.05 m); height 10 ft 6 in (3.20 m); wing area 298.17 sq ft (27.70 m2)
Armament: (all versions) one fixed forward-firing 7.7-mm (0.303-in) machine-gun and one gun of same calibre on trainable mount in rear cockpit, plus up to 220 lb (100 kg) of bombs on external racks
- Two-seat intermediate trainer for the Imperial Japanese Navy.
- Floatplane version, with Amakaze 11 engine.
- Floatplane, with 384 kW (515 hp) Amakaze 21.
- Projected land-based version with 358 kW (480 hp) Amakaze 21A. Never built.
- Projected land-based version with 384 kW (515 hp) Amakaze 15. Never built.