The Mitsubishi Ki-21 

Allied codename 'Sally' or 'Gwen'

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:

• Mitsubishi Ki-21-Ia (*)
• Mitsubishi Ki-21-IIb (*)
• Other Mitsubishi Ki-21 'Gwen' or 'Sally' versions
• Army Type 97 Heavy Bomber versions
• Mitsubishi MC-21 versions
• Allied code names for the Mitsubishi Ki-21

Further pictures:

Mitsubishi Ki-21 'Sally' in full flight


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	-

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

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:

• Good performance
• Excellent handling
• Excellent range

Weaknesses:

• Vulnerable due to lack of armor and fuel tank protection
• Insufficient offensive load, sacrificed to range
• Insufficient defensive armament (early sub versions)

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