 Although used in all fronts in the Pacific theater, it became clear by 1942 that the design was rapidly becoming obsolete, and was increasingly shifted away from front-line service.In spite of its shortcomings, the Ki-21 remained in service until the end of the war, being utilized as transport (along with the civil transport version MC-21), bomber crew and paratrooper trainer, for liaison and communications, special commando and secret missions, and "kamikaze" operations.Nine Ki-21-Ia/b's were sold by Japan to Thailand in 1940 for use by the Royal Thai Air Force against Vichy French forces in French Indochina but did not participate in the French-Thai War as its crews had not completed training.