Mitsubishi Ki-21
Encyclopedia
The (Allied
Allies of World War II
The Allies of World War II were the countries that opposed the Axis powers during the Second World War . Former Axis states contributing to the Allied victory are not considered Allied states...
reporting name
World War II Allied names for Japanese aircraft
The World War II Allied names for Japanese aircraft were reporting names, often described as codenames, given by Allied personnel to Imperial Japanese aircraft during the Pacific campaign of World War II. The names were used by Allied personnel to identify Japanese aircraft for reporting and...
: "Sally" /"Gwen") was a Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
ese bomber
Bomber
A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...
during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. It began operations during the Second Sino-Japanese War
Second Sino-Japanese War
The Second Sino-Japanese War was a military conflict fought primarily between the Republic of China and the Empire of Japan. From 1937 to 1941, China fought Japan with some economic help from Germany , the Soviet Union and the United States...
participating in the Nomonhan Incident, and in the first stages of the Pacific War
Pacific War
The Pacific War, also sometimes called the Asia-Pacific War refers broadly to the parts of World War II that took place in the Pacific Ocean, its islands, and in East Asia, then called the Far East...
, including the Malayan, Burmese
Burma Campaign
The Burma Campaign in the South-East Asian Theatre of World War II was fought primarily between British Commonwealth, Chinese and United States forces against the forces of the Empire of Japan, Thailand, and the Indian National Army. British Commonwealth land forces were drawn primarily from...
, Dutch East Indies
Dutch East Indies campaign
The Dutch East Indies campaign of 1941–1942 was the conquest of the Dutch East Indies by forces from the Empire of Japan in the early days of the Pacific Campaign of World War II. Forces from the Allies attempted unsuccessfully to defend the islands. Indonesia was targeted by the Japanese for its...
and New Guinea Campaign
New Guinea campaign
The New Guinea campaign was one of the major military campaigns of World War II.Before the war, the island of New Guinea was split between:...
s. It was also used to attack targets as far-flung as western China
Western China
Western China , refers to the western part of China. In the definition of the Chinese government, Western China covers six provinces: Gansu, Guizhou, Qinghai, Shaanxi, Sichuan, and Yunnan; one municipality: Chongqing; and three autonomous regions: Ningxia, Tibet, and Xinjiang.-Administrative...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
and northern Australia
Northern Australia
The term northern Australia is generally known to include two State and Territories, being Queensland and the Northern Territory . The part of Western Australia north of latitude 26° south—a definition widely used in law and State government policy—is also usually included...
.
Design and development
In 1936, Imperial Japanese Army Air ServiceImperial Japanese Army Air Service
The , was the land-based aviation force of the Imperial Japanese Army. As with the IJA itself, the IJAAF was developed along the lines of Imperial German Army Aviation so its primary mission was to provide tactical close air support for ground troops while maintaining a limited air interdiction...
issued a requirement for a new heavy bomber
Heavy bomber
A heavy bomber is a bomber aircraft of the largest size and load carrying capacity, and usually the longest range.In New START, the term "heavy bomber" is used for two types of bombers:*one with a range greater than 8,000 kilometers...
to replace both the Ki-20
Mitsubishi Ki-20
-See also:-References:NotesBibliography...
(Army Type 92 Heavy Bomber) and the Ki-1
Mitsubishi Ki-1
|-See also:-External links:* *...
(Army Type 93 Heavy Bomber). The design called for a crew of at least four, top speed of 400 km/h (248.5 mph), endurance of at least five hours, and a bombload of 750 kg (1,653.5 lb). The design parameters were very ambitious, and few twin-engine bombers anywhere in the world could exceed such performance at that time.
Both Mitsubishi and Nakajima
Nakajima Aircraft Company
The Nakajima Aircraft Company was a prominent Japanese aircraft manufacturer throughout World War II.-History:...
were asked to build two prototype
Prototype
A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...
s each, a further proposal from Kawasaki
Kawasaki Heavy Industries
is an international corporation based in Japan. It has headquarters in both Chūō-ku, Kobe and Minato, Tokyo.The company is named after its founder Shōzō Kawasaki and has no connection with the city of Kawasaki, Kanagawa....
being rejected. The Mitsubishi design was an all-metal mid-wing cantilever
Cantilever
A cantilever is a beam anchored at only one end. The beam carries the load to the support where it is resisted by moment and shear stress. Cantilever construction allows for overhanging structures without external bracing. Cantilevers can also be constructed with trusses or slabs.This is in...
monoplane
Monoplane
A monoplane is a fixed-wing aircraft with one main set of wing surfaces, in contrast to a biplane or triplane. Since the late 1930s it has been the most common form for a fixed wing aircraft.-Types of monoplane:...
with retractable landing gear
Undercarriage
The undercarriage or landing gear in aviation, is the structure that supports an aircraft on the ground and allows it to taxi, takeoff and land...
, ventral bomb bay
Bomb bay
The bomb bay or weapons bay on some military aircraft is a compartment to carry bombs, usually in the aircraft's fuselage, with "bomb bay doors" which open at the bottom. The bomb bay doors are opened and the bombs are dropped when over the target or at a specified launching point.Large-sized...
and two radial engine
Radial engine
The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders point outward from a central crankshaft like the spokes on a wheel...
s. The first prototype flew on 18 December 1936, with the second prototype, which differed in replacing the dorsal turret of the first prototype with a long greenhouse canopy, following later in the month. In the resulting competition Mitsubishi's Ki-21 and Nakajima's Ki-19
Nakajima Ki-19
|-See also:-External links:*...
were found to be similar, with the Ki-21 having better performance while the Nakajima design was a better bombing platform and had more reliable engines. In order to make a final decision, two further prototype were ordered from both Mitsubishi and Nakajima, with Mitsubishi instructed to change its own 615 kW Mitsubishi Ha-6 radial engines for the Nakajima Ha-5
Nakajima Ha-5
-Bibliography:* Francillon, R. Japanese Aircraft of the Pacific War. Annapolis: Putnam, 1970. SBN 370 00033 1* Gunston, Bill. World Encyclopaedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9...
engines used by the Nakajima design and vice versa, while the Ki-21 gainied a revised glazed nose similar to that of the Ki-19 and revised tail surfaces. Thus modified, the Ki-21 proved superior, and was ordered into production as the "Army Type 97 Heavy Bomber Model 1A", being ordered into production in November 1937.
Production aircraft began to enter service in August 1938, supplementing and then replacing the Fiat BR.20
Fiat BR.20
The Fiat BR.20 Cicogna was a low-wing twin-engine medium bomber produced from mid-1930s until the end of World War II by the Turin firm. When it entered service in 1936 it was the first all-metal Italian bomber and it was regarded as one of the most modern medium bomber of the world...
bombers which had been purchased as an interim measure.
Several improved versions followed (see below) before the production of the type ended in September 1944. A total of 2,064 aircraft were built, 1,713 by Mitsubishi and 351 by Nakajima.
Operational history
The Ki-21-Ia was used in combat in the war with ChinaSecond Sino-Japanese War
The Second Sino-Japanese War was a military conflict fought primarily between the Republic of China and the Empire of Japan. From 1937 to 1941, China fought Japan with some economic help from Germany , the Soviet Union and the United States...
in autumn 1938, initially with great success, but not in great numbers, as production delays prevented the IJAAF from re-equipping the 60th Sentai and 61st Sentai until the end of 1939. However, combat revealed that the greatest weaknesses of the design were in its lack of armament and self-sealing fuel tank
Self-sealing fuel tank
In aviation, self-sealing fuel tank is a fuel tank technology in wide use since World War II that prevents fuel tanks primarily on aircraft from leaking fuel and igniting after being damaged by enemy fire....
s.
The Ki-21-Ib was an improved version designed to address the armament issue by increasing the number of 7.7 mm (.330 in) Type 89 machine gun
Type 89 machine gun
Type 89 refers to two families of unrelated Imperial Japanese Army aircraft machine guns. The first family is the recoil-operated Vickers gun. The Type 89 FIXED gun was a license-built Vickers E class gun chambered for the Type 89 cartridge . It was used in synchronized applications in fighter...
s to five, and incorporating improvements to the horizontal tail surfaces and trailing edge
Trailing edge
The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge rejoins. Essential control surfaces are attached here to redirect the air flow and exert a controlling force by changing its momentum...
flap
Flap (aircraft)
Flaps are normally hinged surfaces mounted on the trailing edges of the wings of a fixed-wing aircraft to reduce the speed an aircraft can be safely flown at and to increase the angle of descent for landing without increasing air speed. They shorten takeoff and landing distances as well as...
s. In addition, the bomb bay was enlarged. The tail gun was a 'stinger' installation, and was remotely controlled. Also, the fuel tank
Fuel tank
A fuel tank is safe container for flammable fluids. Though any storage tank for fuel may be so called, the term is typically applied to part of an engine system in which the fuel is stored and propelled or released into an engine...
s were partially protected with laminated rubber sheets.
This was followed in production by the Ki-21-Ic with an 500 L (130 US gal) auxiliary fuel tank, fitted in the rear weapons-bay and one more 7.7 mm (.303 in) machine gun, bringing the total to six. Four 50 kg (110.2 lb) bombs were carried externally. To offset the increase in weight the main wheels of the Ki-21-IC were increased in size.
However, by the attack on Pearl Harbor
Attack on Pearl Harbor
The attack on Pearl Harbor was a surprise military strike conducted by the Imperial Japanese Navy against the United States naval base at Pearl Harbor, Hawaii, on the morning of December 7, 1941...
and the start of the Pacific War
Pacific War
The Pacific War, also sometimes called the Asia-Pacific War refers broadly to the parts of World War II that took place in the Pacific Ocean, its islands, and in East Asia, then called the Far East...
, improvements in Republic of China Air Force
Republic of China Air Force
The Republic of China Air Force is the aviation branch of the Republic of China Armed Forces. The ROCAF's primary mission is the defense of the airspace over and around Taiwan...
fighter quality and quantities caused losses to mount, and most Ki-21-1a, -1b and -1c were relegated to training or second-line duties.
Front line units from mid-1940 were equipped with the Ki-21-IIa ("Army Type 97 Heavy Bomber Model 2A") with the more powerful 1118 kW Mitsubishi Ha-101 air-cooled engines and larger horizontal tail surfaces. This became the main version operated by most IJAAF heavy bomber squadrons at the beginning of the Pacific War, and played a major role in many early campaigns. For operations over the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
the JAAF's 5th, 14rd and 62rd Air Groups, based in Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
, attacked American targets at Aparri, Tuguegarao, Vigan and other targets in Luzon
Luzon
Luzon is the largest island in the Philippines. It is located in the northernmost region of the archipelago, and is also the name for one of the three primary island groups in the country centered on the Island of Luzon...
on 8 December 1941. The 3rd, 12th, 60th and 98th Air Groups, based in French Indochina, struck British and Australian targets in Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
and Malaya
British Malaya
British Malaya loosely described a set of states on the Malay Peninsula and the Island of Singapore that were brought under British control between the 18th and the 20th centuries...
, bombing Alor Star
Alor Star
Alor Setar, known as Alor Star between 2004 and 2008, is the state capital of Kedah, Malaysia, and Kota Setar District's Administrative Centre. It is also a distribution center for manufacturing and agricultural products such as paddy, and the royal seat of the Kedah state since the establishment...
, Sungai Petani
Sungai Petani
Sungai Petani is a town in the state of Kedah, in the northern part of Peninsular Malaysia. Sungai Petani is the second largest town in Kedah after Alor Star.-Etmylogy:...
and Butterworth
Butterworth, Penang
Butterworth is the principal town of Seberang Perai in the state of Penang in Malaysia. Named after William John Butterworth, Governor of the Straits Settlements , Butterworth was established in the mid-19th century as a landing place across the channel from the capital of Penang, George Town...
under escort by Nakajima Ki-27
Nakajima Ki-27
The was the main fighter aircraft used by the Imperial Japanese Army Air Force up until 1940. Its Allied nickname was "Nate", although it was called "Abdul" in the "China Burma India" theater by many post war sources; Allied Intelligence had reserved that name for the nonexistent Mitsubishi Navy...
and Ki-43
Nakajima Ki-43
The Nakajima Ki-43 Hayabusa was a single-engine land-based tactical fighter used by the Imperial Japanese Army Air Force in World War II...
fighters. However, starting from operations over Burma in December 1941 and early 1942, the Ki-21 began to suffer heavy casualties from Curtiss P-40
Curtiss P-40
The Curtiss P-40 Warhawk was an American single-engine, single-seat, all-metal fighter and ground attack aircraft that first flew in 1938. The P-40 design was a modification of the previous Curtiss P-36 Hawk which reduced development time and enabled a rapid entry into production and operational...
s and Hawker Hurricane
Hawker Hurricane
The Hawker Hurricane is a British single-seat fighter aircraft that was designed and predominantly built by Hawker Aircraft Ltd for the Royal Air Force...
s.
To partially compensate, the IJAAF introduced the Ki-21-IIb, with a pedal-operated upper turret
Gun turret
A gun turret is a weapon mount that protects the crew or mechanism of a projectile-firing weapon and at the same time lets the weapon be aimed and fired in many directions.The turret is also a rotating weapon platform...
with one 12.7 mm (0.50 in) Type 1 machine gun
Type 1 machine gun
The Type 1 machine gun was developed for aerial use for the Imperial Japanese Army and Navy during World War II. It was an adaptation of the German MG 15 machine gun.-Installations:* Aichi B7A* Mitsubishi Ki-67* Nakajima C6N* Yokosuka D4Y...
, redesigned cockpit
Cockpit
A cockpit or flight deck is the area, usually near the front of an aircraft, from which a pilot controls the aircraft. Most modern cockpits are enclosed, except on some small aircraft, and cockpits on large airliners are also physically separated from the cabin...
canopies and increased fuel capacity. Although used in all fronts in the Pacific theater, it became clear by 1942 that the design was rapidly becoming obsolete, and was increasingly shifted away from front-line service.
In spite of its shortcomings, the Ki-21 remained in service until the end of the war, being utilized as transport (along with the civil transport version MC-21), bomber crew and paratrooper
Paratrooper
Paratroopers are soldiers trained in parachuting and generally operate as part of an airborne force.Paratroopers are used for tactical advantage as they can be inserted into the battlefield from the air, thereby allowing them to be positioned in areas not accessible by land...
trainer
Trainer (aircraft)
A trainer is a class of aircraft designed specifically to facilitate in-flight training of pilots and aircrews. The use of a dedicated trainer aircraft with additional safety features—such as tandem flight controls, forgiving flight characteristics and a simplified cockpit arrangement—allows...
, for liaison
Liaison aircraft
A liaison aircraft is a small, usually unarmed aircraft primarily used by military forces for artillery observation or transporting commanders and messages. The concept developed before World War II and included also battlefield reconnaissance, air ambulance, column control, light cargo delivery...
and communications, special commando and secret missions, and kamikaze
Kamikaze
The were suicide attacks by military aviators from the Empire of Japan against Allied naval vessels in the closing stages of the Pacific campaign of World War II, designed to destroy as many warships as possible....
operations.
Nine Ki-21-Ia/b's were sold by Japan to Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
in 1940 for use by the Royal Thai Air Force
Royal Thai Air Force
The Royal Thai Air Force or RTAF is the air force of the Kingdom of Thailand. Since its establishment in 1913, as one of the earliest air forces of Asia, the Royal Thai Air Force had engaged in many major and minor battles. During the Vietnam war era, the air force has been developed with USAF-aid...
against Vichy French
Vichy France
Vichy France, Vichy Regime, or Vichy Government, are common terms used to describe the government of France that collaborated with the Axis powers from July 1940 to August 1944. This government succeeded the Third Republic and preceded the Provisional Government of the French Republic...
forces in French Indochina
French Indochina
French Indochina was part of the French colonial empire in southeast Asia. A federation of the three Vietnamese regions, Tonkin , Annam , and Cochinchina , as well as Cambodia, was formed in 1887....
but did not participate in the French-Thai War
French-Thai War
The Franco-Thai War was fought between Thailand and Vichy France over certain areas of French Indochina that had once belonged to Thailand....
as its crews had not completed training.
Towards the end of the war, remaining Ki-21s were used by Giretsu Special Forces
Giretsu
was an airborne special forces unit of the Imperial Japanese Army formed from Army paratroopers, in November 1944 as a last-ditch attempt to reduce and delay Allied bombing raids on the Japanese home islands...
in strikes against American forces in Okinawa and the Ryūkyū Islands
Ryukyu Islands
The , also known as the , is a chain of islands in the western Pacific, on the eastern limit of the East China Sea and to the southwest of the island of Kyushu in Japan. From about 1829 until the mid 20th century, they were alternately called Luchu, Loochoo, or Lewchew, akin to the Mandarin...
. One of the noted operations was an attack on the Allied-held Yontan airfield
Yomitan, Okinawa
is a village located in Nakagami District, Okinawa, Japan. As of 30 September 2005, the village has an official population of 38,532. The total area is 35.17 km²....
and Kadena airfield on the night of 24 May 1945. Twelve Ki-21-IIb's of Daisan Dokuritsu Hikotai were dispatched for a strike, each with 14 commando
Commando
In English, the term commando means a specific kind of individual soldier or military unit. In contemporary usage, commando usually means elite light infantry and/or special operations forces units, specializing in amphibious landings, parachuting, rappelling and similar techniques, to conduct and...
s. Five managed to crash-land on the Yontan airfield. Only one plane landed successfully. The surviving raiders, armed with submachine gun
Submachine gun
A submachine gun is an automatic carbine, designed to fire pistol cartridges. It combines the automatic fire of a machine gun with the cartridge of a pistol. The submachine gun was invented during World War I , but the apex of its use was during World War II when millions of the weapon type were...
s and explosives then wrought havoc on the supplies and nearby aircraft, destroyed 264,979 L (70,000 gal) of fuel and nine aircraft, and damaging 26 more.
A number of Ki-21-Ia were modified to serve as military transports for use by Greater Japan Airways, which was under contract by the Japanese Army in China for transportation. Designated "MC-21", these aircraft had all armament and military equipment removed. Used primarily as cargo transports, each could also seat nine paratroopers. Aircraft built from the start as transports were given the separate designation of Mitsubishi Ki-57
Mitsubishi Ki-57
|-See also:-References:NotesBibliography* Francillon, Ph.D., René J. The Mitsubishi Ki-21 . Leatherhead, Surrey, UK: Profile Publications Ltd., 1967....
, with equivalent civil aircraft being designated MC-20.
Code Names
The Ki-21 had more than one Allied codename. Initially called "Jane", the name was quickly changed to "Sally" when GeneralGeneral
A general officer is an officer of high military rank, usually in the army, and in some nations, the air force. The term is widely used by many nations of the world, and when a country uses a different term, there is an equivalent title given....
Douglas MacArthur
Douglas MacArthur
General of the Army Douglas MacArthur was an American general and field marshal of the Philippine Army. He was a Chief of Staff of the United States Army during the 1930s and played a prominent role in the Pacific theater during World War II. He received the Medal of Honor for his service in the...
objected that the name was the same as that of his wife. When the Ki-21-IIb entered service, the absence of the long dorsal "greenhouse" led Allied observers to mistake it for a completely new type, which was designated "Gwen". However, when it was realized that "Gwen" was a new version of the Ki-21, it was renamed "Sally 3", with "Sally 1" referring to the earlier Ha-5 powered models, and "Sally 2" referring to the Ha-101 powered Ki-21-IIa.
Versions
Ki-21- Prototype models with various engines and armament combinations for evaluation. Final version with Nakajima Ha-5 engine. 8 built
Ki-21-Ia (Army Type 97 Heavy Bomber, Model IA)
- First production model, with 634 kW (850 hp) Nakajima Ha-5-kai engines. Most were built by Mitsubishi, 143 manufactured by Nakajima
Ki-21-Ib (Army Type 97 Heavy Bomber, Model IB)
- Improved version with additional 7.7 mm (.303 in) machine guns, larger bomb compartment and flaps, redesigned tail. 120 built by Mitsubishi, 351 (including Ki-21 Ib and Ic) by Nakajima
Ki-21-Ic (Army Type 97 Heavy Bomber, Model IC)
- Improved type with one additional 7.7 mm (.303 in) machine gun, increased fuel capacity, 160 built by Mitsubishi
Ki-21-II
- Evaluation model with more powerful engines, 4 built
Ki-21-IIa (Army Type 97 Heavy Bomber, Model IIA)
- Production model based on Ki-21-IIa, 590 built
Ki-21-IIb (Army Type 97 Heavy Bomber, Model IIB)
- Final production version based on Ki-21-IIa with modified canopy, clear upper cabin replaced by rotating turret, 688 built.
MC-20-I (Army Type 100 Transport, Model I)
- Unarmed civilian transport version, converted from Ki-21-Ia; approximately 100 aircraft were converted
Operators
- Imperial Japanese Army Air Force
- Imperial Japan Airways (Dai Nippon Kōkū)
- Royal Thai Air ForceRoyal Thai Air ForceThe Royal Thai Air Force or RTAF is the air force of the Kingdom of Thailand. Since its establishment in 1913, as one of the earliest air forces of Asia, the Royal Thai Air Force had engaged in many major and minor battles. During the Vietnam war era, the air force has been developed with USAF-aid...
operated nine Ki-21-I Nagoya