 The first prototype of Kawanishi's design, designated E15K1 in the Navy's short designation system made its maiden flight on 5 December 1941.Five more prototypes followed during 1941–42.Problems were encountered with the retractable stabilising floats, resulting in several accidents when the floats could not be lowered for landing, and the system was eventually abandoned, with the stabilising floats being fixed, and a more powerful Mitsubishi MK4S Kasei 24 engine fitted to compensate for the increased drag.