In early 1937 Kawasaki was instructed by the Imperial Japanese army to initiate the design and development of a twin-engine fighter that would be suitable for long-range operations over the Pacific. The concept derived from army interest in developments taking place in other countries, and particularly in the Messerschmitt Bf 110. The first Kawasaki Ki-45 Toryu (dragon killer) prototype flew in 1939, a cantilever mid-wing monoplane with retractable tailwheel landing gear. A slender fuselage provided enclosed accommodation for two in tandem. Problems followed with the engine installation, and it was not until September 1941 that the Ki-45 KAIa entered production. Armament of this initial series version comprised one forward-firing 20mm cannon, two 12.7mm machine-guns in the nose, and a 7.92mm machine-gun on a flexible mount in the rear cockpit; there was also provision to carry two drop tanks or two 250kg bombs on underwing racks. The type entered service in August 1942 but was first used in combat during October 1942, soon being allocated the Allied codename 'Nick'. The Ki-45 KAIa was joined by a new version developed especially for the ground-attack/antishipping role, the Ki-45 KAIb. Standard armament comprised one 20mm cannon in the nose, a forward-firing 37mm cannon in the fuselage, and one rear-firing 7.92mm machine gun, plus the underwing provision for drop tanks or bombs; a number of alternative weapon installations were tried experimentally, including the use of a 75mm cannon for attacks on shipping.
The Ki-45 KAIa was, for its day, heavily armed and proved effective against the USAF's Consoldiated B-24 Liberators and, when these bombers were used more extensively for night operations, the Ki-45 was adapted to attack them. Thus the night-fighting capability of the type was discovered, leading to development of the Ki-45 KAIc night-fighter, which proved to be one of the most successful Japanese aircraft in this category. Ki-45 Toryus remained in service until the end of the Pacific war, production totalling 1,701 including prototypes, being used for the defence of Tokyo, and in the Manchuria, Burma and Sumatra areas of operations.
