The Kawasaki Ki-81 was a heavily armed escort fighter based on the Ki-48 Sokei light bomber. Work on converting the Ki-48 to this new role began early in 1942 and continued into 1943. Four different prototypes were produced to test out different combinations of guns, ranging from the simple use of five 7.7mm Type 89 machine guns up to a more complex version with an electrically or hydraulically operated dorsal turret and armed with a 20mm Ha.5 cannon. The fundamental problem with the design was the placid handling and limited speed of the Ki-48, and the project was eventually abandoned.
The same basic idea saw the development of the Mitsubishi Ki-69, based on the Ki-67 Hiryu, the Nakajima Ki-58, based on the Ki-49 Donryu, and in the United States produced the B-40 and B-41, based on the B-17 Flying Fortress and B-24 Liberator. None of these designs was a success.