7th, 12th, 14th, 58th, 60th, 61st, 62nd, 92nd, 95th, and 98th
- Dokuritsu Hikotai: 3rd
- Hikodan: 22nd
- Hikoshidan Shireibu Hikodan: 1st, 5th, 8th
- Hamamatsu Army Bomber Flying School
Towards the end of 1939 the 60th Hikosentai (air regiment) was equipped with the Ki-21.
Arrival in China
The 60th and 61st Sentai went to China with their Ki-21s in August 1938.
The Ki-21 was the main bomber in December 1941. It was used in the Malayan, Thai, Burmese, and Netherlands East Indies campaigns.
The 5th Air Group, in Formosa, included the 14th and 62nd Hikosentais. They attacked Aparri, Tuguegarao, Vigan, and Luzon on December 8, 1941.
The 3rd Hikoshidan (Air Division), in Indo-China, including the 12th, 60th, and 98th Hikosentais bombed Siam and Malaya. There were a total of 87 Ki-21s.
When faced by P-40s and Hurricanes they suffered many losses.
By 1943 the Ki-21 was obsolete and was moved into secondary rolls. These included being a bomber trainer, communication aircraft, and a suicide plane.
Okinawa Commando Raid
The 3rd Dokuritsu Hikotai (Independent Wing) used Ki-21-IIbs to carry commandos that crash landed on Okinawa and caused much damage to aircraft and supply dumps.