However, starting from operations over Burma in December 1941 and early 1942, the Ki-21 began to suffer heavy casualties from Curtiss P-40s and Hawker Hurricanes.
Namun sejak operasi-operasi di Burma pada Desember 1941 dan awal 1942, Ki-21 mulai mengalami kekalahan dari Curtiss P-40 dan Hawker Hurricane.