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Air Power
Mitsubishi Ki-67 Hiryu (Peggy)
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Resembling as it did a G4M Betty which had been put on a slimming diet, the Japanese Army’s Ki-67 Hiryu (Flying Dragon) was nevertheless the best Japanese twin-engined bomber of the Pacific War. It compared favorably with Allied contemporaries, but despite its official classification by the JAAF as a heavy bomber, it was more in the class of the American B-26 Marauder. Had the Peggy, as the Allies called her, been available before the coming of Allied aerial superiority, the Pacific War’s history might well have been different. Sadly for the Japanese, the plane was forced to fly with young crews fresh out of training school in most cases, and even those veterans who were lucky enough to fly the Hiryu had to operate her under almost suicidal conditions against swarms of high-performing enemy fighters.
Late in 1940, even as Nakajima’s Ki-49 Donryu was undergoing test, the Army Air Staff was drafting specifications for her future successor. The Japanese Army was still preparing for an ultimate showdown with the Soviet Union, and thus wanted a tactical “heavy” bomber. Mitsubishi was therefore instructed to build three prototypes to meet the following requirements: (a) an operating altitude of from 13,125 feet to 22,965 feet; (b) a maximum speed of 342 mph; (c) a radius of action of 435 miles with a 1,102-lb. bombload; (d) a maximum bombload of eight 220-lb. bombs, three 551-lb. bombs, or a single 1,102-lb. bomb; (e) a crew of from six to ten men, depending on the mission profile; (f) a defensive armament comprising one 7.7mm machine gun in each of the nose, port, and starboard positions, and a 12.7mm gun in each of the dorsal and tail positions; and (g) two engines chosen from the following types-the Mitsubishi Ha-101, Nakajima Ha-103, or Mitsubishi Ha-104.
Chief Engineer Ozawa’s team designed a clean, slender mid-wing monoplane powered by a pair of 1,900-hp Ha-104s. As mentioned before, the prototype looked like a G4M Betty that had been dieting, but aside from that, Ozawa made a commendable departure from previous Japanese design methods. To ease production, the Ki-67 was designed to be built by sub-assemblies from the start, and crew armor and self-sealing fuel tanks were also used from the beginning. Attention to these details rather delayed the operational debut of the Hiryu, but they turned out to be strong assets when the plane had to be built, maintained, and flown under the harsh conditions of the late-war period.
The three prototypes were not completed until December 1942, February 1943, and March 1943, respectively, but Mitsubishi had already been instructed to build additional prototypes and service-test machines. All three prototypes were armed similarly-one 7.92mm machine gun in each of the nose, port, and starboard beam positions, and one 12.7mm gun in dorsal and tail turrets. The first prototype left the earth on its maiden flight on December 27, 1942. It displayed some longitudinal instability and control oversensitivity under certain flight conditions, but overall, the Mitsubishi team and the Army were pleased with the new creation. Although the maximum speed was eight miles per hour slower than the specification called for, the Ki-67 easily met or exceeded every other requirement. Once the service-test machines were modified to improve their handling characteristics, the type was discovered to be both easy to fly and amazingly maneuverable. Without a bombload of any kind, the Hiryu could easily loop and turn tightly, and its controls remained smooth and effective even in dives of up to 373 mph. In addition to increased fuel capacity from 565 gallons to 855 gallons-and the extra tanks were self-sealing, no less-the service test examples had a revised armament. The nose gun was changed to a 12.7mm weapon, the dorsal turret’s gun became a 20mm cannon, and the beam positions became “blisters” rather than flush-mounted windows.
In December 1942, it was suggested that the new aircraft would make an excellent land-based torpedo bomber, and in January of the following year, Mitsubishi was instructed to fit an underbelly torpedo rack on 100 production Hiryus. The 17th and 18th production Ki-67s were used to test the plane’s suitability for this demanding role, and Major Sakamoto of the Army’s Air Examination Department took the two planes and their Army crewmen to the Yokosuka Naval Air Station for trials. The Hiryu proved so successful that Mitsubishi was directed to install torpedo racks on all Ki-67s beginning with the 161st aircraft, and the Army agreed to release some Hiryus for Naval service. The JNAF renamed them the Yasukuni, after the shrine near Tokyo devoted to honored war dead.
The Army, in fact, was so pleased with the new bomber, that additional equipment was being continually planned for it, and actual adoption of the Ki-67 for service was delayed because no one apparently could agree on a standardized configuration for it. Finally, the Army Air Staff was forced by the demands of the war to quit dithering. The design was frozen on December 2, 1943, after one last change was made-the beam guns were changed to 12.7mm weapons-and it was formally accepted as the Army Type 4 Heavy Bomber Model 1 Hiryu (Ki-67-I).
The foolish delay in finalizing the design meant that the first combat use of the Peggy didn’t occur until the series of air-sea battles off the Formosan coast in October 1944. The Army’s 7th and 98th Sentais and the Navy’s 762nd Kokutai (Air Group) scored some hits on the American cruisers Houston and Canberra, but failed to sink either vessel (they were towed out of the battle zone), and all three units suffered heavy losses. But from then on, torpedo-carrying Ki-67s of both services fought side-by-side for the remainder of the war, being particularly active in opposing the American landings on Okinawa. In its original bomber role, the Hiryu was used by the JAAF over China, and Hamamatsu-based Ki-67s, staging through Iwo Jima, made repeated attacks on B-29 bases in the Marianas until Iwo was invaded.
Production of the Ki-67-I received the highest-priority rating, but only 698 were built. The parent company, Mitsubishi, built 606 at three different factories; Kawasaki built 91; and the Tachikawa Army Air Arsenal built one. Also, Nippon International Air Industries performed the final assembly of 29 Mitsubishi-built examples. Only one more major change was made: the single 12.7mm machine gun in the tail turret was replaced by a twin-gun mount starting with the 451st example. It was also planned to increase the bombload to 2,756 pounds beginning with the 751st aircraft, but Allied bombings and the December 1944 earthquake, which especially affected engine production, seriously impaired production of this and every other Japanese aircraft.
By the end of the war, several special or experimental versions of the Ki-67 were planned, but only one was actually built-the Ki-109 heavy fighter, described separately. Others that reached the drawing board, and in some cases prototype form, included the following:
- Ha-104 Ru powered Ki-67: The 21st and 22nd Hiryus were modified to test the turbosupercharged engines intended for the Ki-109.
- Ki-67-II: This was a projected version to be powered by two 2,400-hp Ha-214s; the 16th and 17th machines were used as test-beds for this engine.
- Ki-67 glider tug: A standard Ki67-I was used to tow the Manazuru (Crane) transport glider in tests.
- Ki-67-I-KAI: A special suicide-attack version, modified by the Tachikawa Arsenal. All turrets were removed and faired over, the crew reduced to just three, and a long rod protruded from the airplane’s nose, to set off on impact either two standard 1,764-lb. bombs or a special explosive charge weighing 6,393 pounds. Apparently, some of these were built and used operationally, but there is no record of their success, or lack of it.
- I-Go-1A carrier: One Ki-67-I was modified to carry a single I-Go-1A radio-controlled anti-shipping missile under its fuselage.
- Ki-69: Proposed escort-fighter version; not proceeded with.
- Ki-97: Proposed transport version, marrying the wings, tail surfaces, engines and undercarriage of the Ki-67 to a new fuselage intended to carry 21 passengers; not proceeded with.
- Ki-112: Projected multi-seat fighter version; not proceeded with.
Specifications:
Manufacturer: Mitsubishi
Type: Twin-engined Heavy Bomber, Heavy Escort Fighter
Accommodation: Normal crew of six to eight in enclosed cabin; reduced to three for suicide attacks.
Allied Code Name: Peggy
Models: Ki-67-Ia, Ib and Ki-67-II, and Ki-109
First Flight: Early 1943, Ki-109: August 1944
Service Delivery: April 1944
Final Delivery: N/A
Production: 698
Powerplants:
(All Ki-67s except for experimental machines) 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.
(16th and 17th Ki-67s) Two Mitsubishi Ha-214 eighteen-cylinder air-cooled radials, rated at 2,400 hp for take-off, 2,130 hp at 5,905 ft., and 1,930 hp at 27,230 ft.
(21st and 22nd Ki-67s) Two Mitsubishi Ha-104 Ru eighteen-cylinder turbosupercharged air-cooled radials, rated at 1,900 hp for take-off and 1,810 hp at 24,150 ft.
Dimensions:
Wingspan: 73 ft. 9 13/16 in.;
Length: 61 ft. 4 7/32 in.;
Height: 25 ft. 3 5/32 in.;
Wing area: 708.801 sq. ft.;
Empty weight: 19,068 lb.;
Loaded weight: 30,347 lb.;
Maximum weight: N/A;
Wing loading: 42.8 lb./sq. ft.;
Power loading: 8 lb./hp;
Performance:
Maximum speed: 334 mph at 19,980 ft.;
Cruising speed: 249 mph at 26,245 ft.;
Climb: To 19,685 ft. in 14 min. 30 sec.;
Service ceiling: 31,070 ft.;
Normal range: 1,740 miles; maximum range, 2,360 miles.
Armaments:
Guns:
(1st, 2nd, and 3rd prototypes) One flexible 7.92mm machine gun in each of the nose, port beam, and starboard beam positions, and one 12.7mm machine gun in each of the dorsal and tail turrets.
(4th-19th Ki-67s) One flexible 7.92mm machine gun in each of the beam positions, one flexible12.7mm machine gun in the nose and in the tail turret, and one 20mm cannon in the dorsal turret.
(20th-450th Ki-67s) One flexible 12.7mm machine gun in each of the nose, port and starboard beam, and tail positions, and one 20mm cannon in the dorsal turret.
(451st and subsequent Ki-67s) One flexible 12.7mm machine gun in each of the nose and beam positions, twin flexible 12.7mm machine guns in the tail turret, and one 20mm cannon in the dorsal turret.
Bombload:
Normal: 1,102 lbs.
Maximum: 1,764 lbs.
Torpedo attack: One 1,764-lb. or One 2,359-lb. torpedo.
Suicide attack: Up to 6,393 lbs.
A standard Ki-67-I waits for take-off while crews are briefed; Formosa, 1944.
Rear view of a Ki-67-I being refueled.
Close-up of the experimental I-Go-IA anti-shipping missile slung under a Ki-67's belly.
Naval personnel loading a torpedo under a Ki-67
A torpedo-carrying Ki-67 taxis out for a mission.
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