The Mitsubishi Ki-21 

Allied codename 'Sally' or 'Gwen'

Japan
Japan

Sorry, No ID pictures yet

The Ki-21 (Ki = Kitai = Airframe) was to the Japanese Army what the G4M 'Betty' was to the Japanese Navy: their best bomber. Both aircraft were built by Mitsubishi, had an excellent performance and incredible range, but at the cost of structural strength, offensive warload, and armor protection.
The type was the result from a February 1936 requirement for a modern bomber to replace both the Mitsubishi Ki-20 (Army Type 92 Heavy Bomber) and the Mitsubishi Ki-1 (Army Type 93 Heavy Bomber). It was a clean monoplane of essentially all-metal construction with fabric-covered control surfaces, a oval-section fuselage with enclosed accommodation, a plain tail unit of cantilever construction, a cantilever mid-set dihedraled wing that was tapered in thickness and chord and carried inboard flaps and outboard ailerons it its trailing edges, and tailwheel landing gear that included main units that retracted into the underside of the nacelles for the two wing-mounted engines.
The first of eight prototype and service trials aircraft made its maiden flight in December 1936 with a powerplant of two Mitsubishi Ha-6 radial piston engines each rated at 825 hp (615 kW) and driving a three-blade metal propeller of the variable-pitch type, and the type was later ordered into production as the Ki-21-Ia or Ki-21-I Ko.

Versions:

Further pictures:

Mitsubishi Ki-21 'Sally' in full flight
Mitsubishi Ki-21 'Sally' in full flight

Another nice view of a Mitsubishi Ki-21
Another nice view of a Mitsubishi Ki-21

 

Technical data on the Mitsubishi Ki-21-Ia
Powerplant 2 × Nakajima Ha-5 KAI Army Type 97 radial, rated at 1080 hp (805.13 kW) each Role during war
  • Heavy Bomber
Length 52 ft 5.9 inch Height 14 ft 3.4 inch
Empty weight 10342 lb Operational weight 16517 lb typical,
17452 lb max
Wing Span 73 ft 9.8 inch Wing Aspect ratio 7.27
Wing Area 749.165 sq ft Service ceiling 28215 ft
Maximum speed 268 mph at 13125 ft Cruising speed unknown
Initial climb rate Climb to 16,405 ft in 13 min 55 sec Range 932 miles typical,
1680 miles max
Fuel capacity internal 690 Imp gal (828 US gal) Fuel capacity external -
Machine guns
  • 1 × 0.303 inch Type 1 trainable in the dorsal turret
  • 1 × 0.303 inch Type 89 trainable forward-firing in the nose position
  • 1 × 0.303 inch Type 89 trainable rearward-firing in the ventral position
Cannons -
Bomb load Up to 2,205 lb, carried in a under fuselage weapons bay rated at 2,205 lb. General disposables load consisted of:
  • up to 2,205 lb of bombs
Torpedoes/rockets -
Crew 7: pilot, co-pilot, navigator/bombardier, radio operator/gunner, up to three gunners (2 optional) Naval or ground based Ground
First flight (prototype) December 1936 Operational Service 1939 - 1945
Manufacturer Mitsubishi Jukogyo K.K. Number produced 2.064 total, 143 this version + unknown out of 351 built by Nakajima
Metric system
Length 16 m Height 4.35 m
Empty weight 4691 kg Operational weight 7492 kg typical,
7916 kg max
Wing Span 22.5 m Wing Aspect ratio 7.27
Wing Area 69.6 m² Service ceiling 8600 m
Maximum speed 431 km/h at 4000 m Cruising speed unknown
Initial climb rate Climb to 5.000 m in 13 min 55 sec Range 1500 km typical,
2704 km max
Fuel capacity internal 3.135 liters Fuel capacity external -
Machine guns
  • 1 × 7,7 mm Type 1 trainable in the dorsal turret
  • 1 × 7,7 mm Type 89 trainable forward-firing in the nose position
  • 1 × 7,7 mm Type 89 trainable rearward-firing in the ventral position
Cannons -
Bomb load Up to 1.000 kg, carried in a under fuselage weapons bay rated at 1.000 kg. General disposables load consisted of:
  • up to 1.000 kg of bombs
Torpedoes/rockets -

Technical data on the Mitsubishi Ki-21-IIb
Powerplant 2 × Mitsubishi Ha-101 Army Type 100 radial, rated at 1500 hp (1118.23 kW) each Role during war
  • Heavy Bomber
Length 52 ft 5.9 inch Height 14 ft 3.4 inch
Empty weight 13382 lb Operational weight 21407 lb typical,
23291 lb max
Wing Span 73 ft 9.8 inch Wing Aspect ratio 7.27
Wing Area 749.165 sq ft Service ceiling 32810 ft
Maximum speed 302 mph at 15485 ft Cruising speed 236 mph at 16405 ft
Initial climb rate Climb to 19,685 ft in 13 min 13 sec Range 1680 miles max
Fuel capacity internal 690 Imp gal (828 US gal) Fuel capacity external -
Machine guns
  • 1 × 0.5 inch Type 1 trainable in the dorsal turret
  • 1 × 0.303 inch Type 89 trainable forward-firing in the nose position
  • 1 × 0.303 inch Type 89 trainable rearward-firing in the ventral position
  • 1 × 0.303 inch trainable rearward-firing in the tail position
  • 2 × 0.303 inch type 89 trainable lateral-firing, one in each of the beam positions
Cannons -
Bomb load Up to 2,205 lb, carried in a under fuselage weapons bay rated at 2,205 lb. General disposables load consisted of:
  • up to 2,205 lb of bombs
Torpedoes/rockets -
Crew 7: pilot, co-pilot, navigator/bombardier, radio operator/gunner, up to three gunners (2 optional) Naval or ground based Ground
First flight (prototype) December 1936 Operational Service 1939 - 1945
Manufacturer Mitsubishi Jukogyo K.K. Number produced 2.064 total, 688 this version
Metric system
Length 16 m Height 4.35 m
Empty weight 6070 kg Operational weight 9710 kg typical,
10565 kg max
Wing Span 22.5 m Wing Aspect ratio 7.27
Wing Area 69.6 m² Service ceiling 10000 m
Maximum speed 486 km/h at 4720 m Cruising speed 380 km/h at 5000 m
Initial climb rate Climb to 6.000 m in 13 min 13 sec Range 2704 km max
Fuel capacity internal 3.135 liters Fuel capacity external -
Machine guns
  • 1 × 12,7 mm Type 1 trainable in the dorsal turret
  • 1 × 7,7 mm Type 89 trainable forward-firing in the nose position
  • 1 × 7,7 mm Type 89 trainable rearward-firing in the ventral position
  • 1 × 7,7 mm trainable rearward-firing in the tail position
  • 2 × 7,7 mm type 89 trainable lateral-firing, one in each of the beam positions
Cannons -
Bomb load Up to 1.000 kg, carried in a under fuselage weapons bay rated at 1.000 kg. General disposables load consisted of:
  • up to 1.000 kg of bombs
Torpedoes/rockets -

Here is a quick overview of all different versions, without the full technical specifications:

Different versions of the Mitsubishi Ki-21 
Mitsubishi Ki-21 prototypes This first production version was preceded by 2 prototypes. These were built at Mitsubishi's 5th Airframe Works in Nagoya and were finished in December 1936. The most distinctive difference was the dorsal turret. Whereas the first prototype had a semi-hemispherical turret, the second prototype had a long greenhouse.
From March 1937 on the Ki-21's were pitted against the Nakajima Ki-19 prototypes. Tests ended in June 1937 when bombing trials were held at Hamamatsu. Since both aircraft had their strengths and weaknesses, both manufacturers were ordered to deliver additional prototypes. Mitsibishi was furhtermore ordered to use 2 × Nakajima Ha-5 engines instead of the Mitsubishi one, in order to improve the reliability, handling and stability. The third prototype was powered as such, and had a redesigned vertical tail to improve stability during the bombing run. When competitive tests were held once more the Ki-21 easily won from the Ki-19, and the last 5 prototypes were used as service trials aircraft.
Number built: 8
Mitsubishi Ki-21-Ia In November 1937 the Ki-21 was ordered into production,with the designation Ki-21-Ia, or Army Type 97 Heavy Bomber Model 1A. It was identical to the Ha-5 protoypes, except that fuel was increased from 405 Imp gal (486 US gal, 1.840 liters) to 580 Imp gal (697 US gal, 2.635 liters).
Number built: 143 plus unknown out of 351 -Ia, -Ib, -Ic versions built by Nakajima
Mitsubishi Ki-21-Ib The first operational trial with the Mitsubishi Ki-21-Ia showed that the aircraft was had inadequate defensive armament, and the lack of fuel protection made them even more vulnerable. One of the main differences was the armament, which was augmented from 3 × 0.303 inch (7,7 mm) guns to the original 3 plus 2 more, 1 in the beam position, and 1 in the tail. This last gun was a 'stinger' installation, and was remotely controlled. Also the fuel tanks were partially preotected by laminated rubber sheets. The bomb-bay was enlarged, the landing flaps were enlarged, and the horizontal tail surfaces were increased in area as well.
Number built: 120 plus unknown out of 351 -Ia, -Ib, -Ic versions built by Nakajima
Mitsubishi Ki-21-Ic This version was mainly like the -Ib, but had an additional lateral gun, and an auxiliary fuel tank of 110 Imp gal (132 US gal, 500 liters), fitted in the rear weapons-bay. When this tank was installed four 110 lb (50 kg) bombs would be carried externally. To offsetthe increase in weight the mainwheels of the Ki-21-Ic were increased in size as well.
Number built: 160 plus unknown out of 351 -Ia, -Ib, -Ic versions built by Nakajima
Mitsubishi Ki-21-II These aircraft had all changes incorporated of the Mitsubishi Ki-21-IIa, and were build as service trials aircraft proving the concept.
Number built: 4
Mitsubishi Ki-21-IIa Although the -Ib and -Ic versions performed well during the war in China in 1939, it was recognised that there was only a token resistance from the Chinese airforce. To be prepared for a bigger War, the Army instructed Mitsubishi to increase the ceiling and speed of the Ki-21.
The resulting aircraft were powered by 2 × Mitsubishi Ha-101 14-cylinder air-cooled radials, rated at 1,500 hp (1.118 kW) each. Most of the aircraft's original design was retained, like the fuel tankage, armament and other systems, but the area of the horizontal tail surfaces were increased once more.
To test the changes incorporated, 4 service trials aircraft were built before the
Number built: 590
Mitsubishi Ki-21-IIb This was the final production version of the Ki-21. It differed from the Mitsubishi Ki-21-IIa with respect to the dorsal turret, which carried a 0.50 inch (12,7 mm) Type 1 trainable gun, and an increased fuel capacity.
Number built: 668
Mitsubishi MC-21 While Japan was waging a war with China it found it had not enough transport aircraft. The Ki-12-Ia's had previously been withdrawn from front-line service, and it was decided that some would be modified as transports.
The aircraft were delivered to the Dai Nippon Koku K.K. (Greater Japan Air Lines Co Ltd.), which had a contract with the Japanese army for transportations.
The modified aircraft were mostly used for transporting goods, but could be used as paratroop transport as well. In the latter case nine troops could be seated in a primitive cabin. Later most aircraft were modified further, and received a metal fairing in place of the glazed nose.
Number converted: unknown
Army Type 97 Heavy Bomber Model 1A Official Imperial Japanese Army Air Force designation for the Mitsubishi Ki-21-Ia 'Sally'
Army Type 97 Heavy Bomber Model 1B Official Imperial Japanese Army Air Force designation for the Mitsubishi Ki-21-Ib 'Sally'
Army Type 97 Heavy Bomber Model 1C Official Imperial Japanese Army Air Force designation for the Mitsubishi Ki-21-Ic 'Sally'
Army Type 97 Heavy Bomber Model 2A Official Imperial Japanese Army Air Force designation for the Mitsubishi Ki-21-2a 'Sally'
Army Type 97 Heavy Bomber Model 2B Official Imperial Japanese Army Air Force designation for the Mitsubishi Ki-21-2b 'Sally'
Mitsubishi Ki-21 Allied codenames The Ki-21 has received more then one codenames. The first name tagged to the Ki-21 was 'Jane', named after General; MacArthur's wife. The General however, didn't appreciate this and the name was quickly changed to 'Sally'. Later, when the Ki-21-IIb entered service the absence of the long dorsal greenhouse (which was one of 'Sally's' main recognition features) led the Allied to think it was a new type, which was designated 'Gwen'. When the type was then properly identified as being a version of the Ki-21, it was then renamed to 'Sally 3', 'Sally 1' referring to the Ha-5 powered models, and 'Sally 2' referring to the Ha-101 powered Ki-21-IIa.

Remarks:

The Ki-21 was the Japanese Army Air Force's main bomber. It had an excellent range, and sufficient performance during the early War years to have a tactical advantage.
The Ki-21 opened it's account in China during the autumn of 1938, where the aircraft was superior to most Chinese air opposition. It performed wel because opposition was almost non-existent, and the strengths of the Ki-21 could be exploited without suffering the weaknesses.
Nevertheless, the Japanese Army instructed Mitsubishi to increase the speed and ceiling of the Ki-21 as a preparation for a bigger War to come. The enhanced version was in time to re-equip most Heavy Bomber groups of the Imperial Japanese Army Air Force when the War broke out in the Pacific.
The main task of the Army Air units was supporting the invasion of Thailand, Burma and Malaya, all the while keeping up the pressure in the Chinese theatre. The first seven months of the Pacific War the Ki-21 supported ground operations in Southeast Asia and the Netherlands East Indies, and were co-instrumental in the fall of Rangoon and Hong Kong. During this time the first serious opposition arose in the form of Curtiss P-40's and Hawker Hurricanes, and losses started to increase.
By 1943 the newest version of the Ki-21 entered service, but by then the Ki-21 started to show it's age and weaknesses. Nevertheless the ki-21 had to soldier on, because the Japanese air industry failed to deliver a replacement. The War was bt\y then reversed as well, and the Ki-21 was more and more used in a defensive role. Being on the offensive, the main advantages of excellent range were of no use, and the weaknesses were even more painfully clear without effective fighter cover. When finally the replacement arrived (the Nakajima Ki-49) a lot of aircraft were used for special operations.
One of the operations was the attack on the Allied held airfield Yontan. Nine Ki-12-IIb's were despatched for a strike, and one of the aircraft managed to crash-land on the airfield close to supplies and aircraft. Japanese commando's then wreaked havoc on the supplies and nearby aircraft, causing considerable damage.

Strengths:

Weaknesses:

 

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© by Frans Bonné, 2000
Last revision: 5/20/01