A single engined two-seat biplane, 211 K4Ys were built between 1933 and 1940, serving as the Imperial Japanese Navy's basic floatplane trainer throughout the Second World War.

In 1930, the Imperial Japanese Navy Air Service's basic seaplane trainer was the Yokosuka K1Y or Type 13 Seaplane Trainer, which had been in use from 1925, and it instructed the First Naval Air Technical Arsenal based at Yokosuka to design a replacement.

[2] Yokosuka built two prototypes, powered by 90 hp (67 kW) Hatakaze four-cylinder air-cooled inline engines in 1930, flying in 1930, and after successful testing, a version powered by a 130 hp Gasuden Jimpu[2] radial engine was ordered into production as the Navy Type 90 Seaplane trainer, with the short designation K4Y1.

[3] The K4Y1 started to replace the K1Y from 1933, remaining the Imperial Japanese Navy Air Service's principal basic seaplane trainer throughout the Pacific war.

[2][3] Data from Japanese Aircraft, 1910-1941[4]General characteristics Performance