 Mitsubishi and Kawasaki were requested to build two prototypes each by December 1936.The specification called for a top speed of at ; normal operating altitude from , the ability to climb to within 8 minutes and an engine to be selected from the Mitsubishi Ha-6 radial, Nakajima Ha-5 radial, or Kawasaki Ha-9-IIb liquid-cooled inline engines, a normal bomb load of and a maximum of , one forward-firing machine gun and one flexible rearward-firing machine gun, the ability to perform 60-degree dives for dive bombing, and a loaded weight less than .The first Kawasaki prototype flew in March 1937; seven more prototypes were produced.