With the Ki-100 proving such a success, it was decided to initiate production of this aircraft, the resulting Ki-100-Ib differing only by having the cutdown rear fuselage and all-round-view canopy that had been designed for the proposed Ki-61-III.
The P-51H was the final production Mustang and used the new V-1650-9 engine, a version of the Merlin that included Simmons automatic supercharger boost control with water injection, allowing War Emergency Power as high as 2,218 hp.