The Ki-109 was one of Japan’s answers to the threat American bombers posed to the Japanese mainland. The concept was simple, and similar to the Rikugun Ki-93 in layout if not intended purpose — put a very large cannon in a twin-engined plane, in this case an interceptor that could take down well-defended U.S. planes in a single shot from a distance.
It was based on the Ki-67 bomber, which had a proven record and such good maneuverability that the Army decided to convert it into a heavy fighter. Initially the plan was for there to be a pair of “hunters” with one holding what was at the time very bulky radar equipment, and the other the big gun in the nose. That plan was dropped and it was decided that the plane variant with the big gun would go hunting alone. It was equipped in its nose with a 75mm Type 88 Heavy Cannon, and had only a .22 caliber tail gun, revised from the bomber version which held multiple machine gun positions. It deleted the bomb bay and side and top gunner positions, and required less of a crew accordingly – down from 6-8 to only 4.
Due to the weight savings and improved aerodynamics of the Ki-109 it is fair to assume that while sharing flight characteristics with its already agile Ki-67 bomber roots, it would have performed even better than the Ki-67 in flight. As a side note, the first few copies of the Ki-109 early production models are said to have actually kept the full defensive armament of the Ki-67, marked and intended for flight with the 107th Army Group. Whether this would have been good or bad in practice can be debated, but the additional cost of materials and crew for the Ki-109’s bomber hunter mission were not justified in the final production versions, and so those positions were deleted. Since the Ki-109 was not intended for bombing missions, it also saved the weight of being laden with bombs.
Unfortunately for Imperial Japan, in practice the Ki-109s were too little, too late to be sent off on their intended missions as the US changed their bombing tactics, and the Army decided not to continue to use them as bomber hunters. It is reported that most were either converted back to Ki-67s or into suicide bombers later in the war.
In Games: The Ki-109 would make an interesting addition to games and would be an easy conversion from Ki-67. They would offer even more fun where the game does not indicate from a distance what the plane is with big red letters. Expecting a Ki-67? Surprise!
Crew of four with pilot, co-pilot, and radio operator in forward cabin, and gunner in tail turret.
Two Mitsubishi Ha-104 eighteen-cylinder air-cooled radial engines, rated at 1,900 hp for take-off, 1,810 hp at 7,220 ft., and 1,610 hp at 20,015 ft.
One forward-firing 75mm cannon in nose and one 12.7mm machine gun in tail turret.
Dimensions, weights, and performance:
Wingspan, 73 ft. 9 13/16 in.
length, 58 ft. 10 11/16 in.
height, 19 ft. 1 1/32 in.
wing area, 708.801 sq. ft.
empty weight, 16,367 lb.
loaded weight, 23,810 lb.
wing loading, 33.6 lb./sq. ft.
power loading, 6.3 lb./hp
maximum speed, 342 mph at 19,980 ft.
cruising speed, 249 mph at 26,245 ft.
normal range, 1,367 miles
Ki 109 Scale Model by Chris Durden – Note the faired over spots where defensive gunner positions once were on the Ki-67