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
favourably 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
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 armour 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.
Rear view of a Ki-67-I being refuelled.
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 manoeuvrable. 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 honoured war
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).
Close-up of the experimental I-Go-IA anti-shipping missile slung under
a Ki-67's belly.
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.
Naval personnel loading a torpedo under a Ki-67.
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 turbo supercharged 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
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.
A torpedo-carrying Ki-67 taxis out for a mission.
Hiryu (Peggy) Technical Data
Twin-engined “heavy” bomber, of all metal construction.
Normal crew of six to eight in enclosed cabin; reduced to three for
(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 turbo
supercharged air-cooled radials, rated at 1,900 hp for take-off and
1,810 hp at 24,150 ft.
(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.
Torpedo attack-one 1,764-lb. or one 2,359-lb. torpedo.
Suicide attack-up to 6,393 lbs.
Dimensions, weights, and performance:
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;
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.