Mitsubishi Ki-21, part three

 

To compensate for the heavy losses against both the Hawker Hurricane and the Curtiss P-40 which the Ki-21 had to fight after Pearl Harbor, the Imperial Japanese Army Air Force (IJAAF) introduced the Ki-21-IIb, which replaced the long greenhouse style dorsal canopy by a turret equipped with a single 12,7 mm (0,5 in) Type 1 machine gun. Cockpit canopies were redesigned as well and fuel capacity was also increased. Although the Ki-21 was used in every front of the Pacific War, it was obvious that by, as early as 1942, the design was starting to be obsolete and was increasingly being shifted away from front-line service. 

In spite of its obsolescence, it remained in service until the end of the war in various roles, like transport, bomber crew and paratroop trainer, liaison and communications, special commando and secret missions and kamikaze operations. 

Near the end of the war, during the Battle of Okinawa, the remaining Ki-21s were used by Giretsu Special Forces (Giretsu was an special forces unit comprised of paratroopers) were used in strikes in Okinawa and American targets on Ryukyu islands. One noted operation was an strike on the American-held Yontan and Kadena airfields on the night of 24th May 1945. Twelve modified Ki-21-IIb with their turrets removed, of the Daisan Dokuritsu Hokutai were sent to strike, each airplane loaded with 14 commandos. Five Ki-21s managed to crash land on Yontan, only one landed successfully. The remaining raiders, armed with sub-machine guns and explosives wrought havoc on the supplies and nearby aircraft, destroying 264.979 L (70.000 US Gal) of fuel and nine aircraft, and damaging 26 more on what was the last operational usage of this Japanese bomber.

The Allied codename for the type, initially was "Jane", but it was quickly changed to "Sally" as "Jane" was the name of Douglas McArthur's wife. When the Ki-21-IIb entered service, the absence of the long greenhouse canopy confused Allied observers, who thought it was a completely new type and named it "Gwen", however, it was quickly switched back to "Sally" when they realized their mistake. 

A total of 2.064 units of every variant were manufactured,  between March 1938 and 1944 when the last Ki-21-IIb was completed.

Sources:

1. https://en.wikipedia.org/wiki/Mitsubishi_Ki-21

2. https://www.valka.cz/Micubisi-Ki-21-Sally-t31499 (translated)

3. http://www.asisbiz.com/il2/Ki-21-Sally/Mitsubishi-Ki-21-Sally.html

Mitsubishi Ki-21, part two

 

Losses for the Ki-21 were high during early combat operations due to an insufficient defensive armament - the Ki-21-Ia was armed with three 7.7mm Type 89 machine guns in nose, ventral and dorsal positions - and self-sealing fuel tanks, with the aircraft's fuel system proving to be unreliable. To address those problems, the Ki-21-Ib was introduced. An additional defensive machine gun was introduced in the tail in an 'stinger' arrangement and was remotely controlled. Both horizontal tail surfaces and trailing edge flaps were improved and the bomb bay was enlarged. Fuel tanks were also partially protected with laminated rubber sheets. 

A third variant of the Ki-21-I was introduced in 1940. This variant had an additional 500 L (130 US Gal) auxiliary fuel tank, fitted in the rear weapons bay and two more machine gun placed in the beam position, making a total of six. Underwing hardpoints were also fitted to carry a total of four 50 Kg (110 lb) bombs externally and, in order to compensate for the increase in weight, the wheels were increased in size. 

By the time of the attack on Pearl Harbor and the start of the Pacific War, the Imperial Japanese Army Air Force's (IJAAF) main antagonist until then, the Republic of China Air Force (ROCAF) had been greatly improved to the point that the Ki-21-I's losses were mounting too high, so most Ki-21-Ia and some 21-Ib were relegated to second line and training duties. 

Front line units were equipped, from mid 1940 onwards with the Ki-21-IIa (Army Type 97 Heavy Bomber Model 2A). This variant was powered by the much powerful Mitsubishi Ha-101 radial engine which yielded up to 1.500 hp of power and was also equipped with larger horizontal tail surfaces. This variant was the standard for many IJAAF's heavy bomber squadrons at the beginning of the Pacific War and played a major role in the early campaigns of the War. For operations over the Philippines, IJAAF's 5th, 14th and 62nd Sentais (a Japanese unit equivalent to a Wing or Group), based in Formosa, attacked American targets at Aparri, Tuguegarao, Vigan and other targets in Luzon island on 8th December 1941. The 3rd, 12th, 60th and 98th Sentais, based in French Indochina bombed British and Australian positions in Thailand and Malaya attacking Alor Star, Sungai Petani and Butterworth (Penang) escorted by Nakajima Ki-27 and Ki-43 fighters. However, during those operations, the Ki-21 suffered heavy losses both from the Hawker Hurricane and the Curtiss P-40 Warhawk.

Sources:

1. https://en.wikipedia.org/wiki/Mitsubishi_Ki-21

2. https://www.valka.cz/Micubisi-Ki-21-Sally-t31499 (translated)

3. http://www.asisbiz.com/il2/Ki-21-Sally/Mitsubishi-Ki-21-Sally.html

MItsubishi Ki-21, part one

 

Back in 1936, the Imperial Japanese Army issued a requirement for a new heavy bomber to replace the Mitsubishi Ki-20 and the Mitsubishi Ki-1 bombers which were clearly outdated for the time. The requirement called for a crew of at least four men, a top speed of 400 km/h (250 mph) with an endurance of at least five hours and a bomb payload of 750 kg (1.650 lb). Those technical requirements were very ambitious for the time and very few twin-engine bombers could achieve such performance numbers.

Mitsubishi and Nakajima were asked to submit their proposals, with Kawasaki's one being rejected. Mitsubishi's design was an all-metal mid-wing cantilever monoplane with a retractable landing gear, ventral bomb bay and two Mitsubishi Ha-6 radial engines. 

The first prototype flew for the first time on 18th December 1936, with the second prototype, which differed from the first one in having a long greenhouse canopy instead of a ventral turret, flying in January 1937. In the ensuing competition against Nakajima Ki-19 (Nakajima's proposal), they found to be similar in performance numbers, being the Ki-21 better in speed and endurance and the Ki-19 being better as a bombing platform and its Nakajima Ha-5 engines being more reliable. In order to make a decision, two more prototypes were ordered from both Mitsubishi and Nakajima, with Mitsubishi ordered to switch its own 825 hp Ha-6 engines for the Ha-5 ones, used by Nakajima and vice versa. That third prototype of the Ki-21 featured a glazed nose similar to the Ki-19 and revised tail surfaces. Therefore, the Ki-21 proved to be superior and was ordered into production as the "Army Type 97 Heavy Bomber Model 1A" in November 1937.

Production aircraft began to enter service in August 1938, supplementing and replacing the Fiat Br.20 Italian bombers that had been purchased as an interim measure. 

The Ki-21-Ia was used in combat for the first time during the Second Sino-Japanese War by the 60th Sentai (an unit equivalent to an aviation Group or Wing in other air forces) from autumn 1938, performing long-range unescorted missions together with the Br.20 of the 12th and 98th Sentais. The Ki-21 proved to be more reliable, robust and better suited for the long Asian distances than the Br.20. Two additional Sentais, the 58th and the 61st were deployed to Manchuria in the summer of 1939 to operate against China, with aircraft of the 61st being heavily employed against Soviet and Mongolian forces during the Nomohan incident (AKA Battles of Khalkin Gol) in June-July 1939, when the Japanese forces launched their main attack.

Sources:

1. https://en.wikipedia.org/wiki/Mitsubishi_Ki-21

2. https://www.valka.cz/Micubisi-Ki-21-Sally-t31499 (translated)

Mitsubishi Ki-21, foreign users

 

The Mitsubishi Ki-21 was a Japanese twin-engined bomber which took part in the World War II. Its main user was Japan, however, it was used by some other users:

• France: After the War, some few Ki-21 were used in Indochina by the French Armée de l'Air (French Air Force) during the First Indochina War. They were originally Ki-21-IIb bombers converted ad-hoc into transports with their defensive armament removed. These machines were very worn out so their usage through that conflict wasn't very prolonged and they were most likely, replaced. 
• Manchukuo: The Manchukuo Imperial Air Force had 6 Ki-21-Ia bombers in strength in the year 1941. They were assigned to 2nd Air Unit, based in Fengtian, but, most probably, they were not used very much and were either destroyed on ground or left to rot. 
• Thailand: Nine Ki-21-IIa bombers were sold to the Kingdom of Thailand in 1940 to be used by the Royal Thai Air Force against the Vichy French forces in Indochina. However they couldn't take part in the Franco-Thai War as crews didn't complete training in time. They were part of the 62nd Squadron and were based at Don Muang, in Bangkok. In 1942, when the Japanese Army invaded Burma, the Thai Army invaded the Shan States, using their Ki-21 extensively against the defending Chinese forces. Two Thai Ki-21s were lost on air raids on 2nd May 1943 and 30th November 1944 when they were based in Lampang, North-West of Thailand. The remaining seven were kept in active after the war and it wasn't until 1949 that they were written off service and were immediately scrapped.

Sources:

1. https://en.wikipedia.org/wiki/Mitsubishi_Ki-21

2. https://en.wikipedia.org/wiki/Manchukuo_Imperial_Air_Force

3. https://www.traditions-air.fr

4. http://wings-aviation.ch/51-Profiles/M/M-Basis-en.htm (translated)