• World War Two
• Imperial Japanese Army (IJA)
• Ki-45 Kai Ko (甲) - one 20 mm Ho-3 ventral cannon, two Ho-103 12.7 mm in the nose and one flexible 7.92 mm in the back position
• Ki-45 Kai Otsu (乙) -  the 20 mm Ho-3 ventral cannon replaced by one 37 mm type 94 anti-tank gun
• Ki-45 Kai Hei (丙) - one 37 mm Ho-203 automatic cannon in the nose (for naval target), one flexible 7.92 mm machine gun in the back position.
• Ki-45 Kai Tei (丁) - modified Type Otsu (乙), as night fighter, equipped with one 37 mm Ho-203 cannon in nose and two fixed 20 mm Ho-5 cannons in a Schräge Musik-style dorsal frontal position, and one flexible 7.92 mm Type 98 machine gun in the back position.
• Ho-203 - Japanese 37 mm autocannon. It was fed by a 15-round closed-loop ammunition belt. It was operationally used only as the nose gun of the Kawasaki Ki-45-KAI heavy fighter, for anti-bomber operations of Imperial Japanese Army (IJA), and on the upper fuselage of Mitsubishi Ki-46.

- removing the paint on the upper fuselage and the back-seat --> reduce the weight and resistance, lighter and faster, for attacking high-altitude bombers (B-29).