https://en.wikipedia.org/wiki/Mitsubishi_Ki-21
The Mitsubishi Ki-21 (or "Type 97 Heavy Bomber") (Allied reporting name:
"Sally" /"Gwen") was a Japanese bomber during World War II. It began operations
during the Second Sino-Japanese War participating in the Nomonhan Incident, and
in the first stages of the Pacific War, including the Malayan, Burmese, Dutch
East Indies and New Guinea Campaigns. It was also used to attack targets as
far-flung as western China, India and northern Australia.
In 1936, Imperial Japanese Army Air Service issued a requirement for a new heavy
bomber to replace both the Ki-20 (Army Type 92 Heavy Bomber) and the Ki-1 (Army
Type 93 Heavy Bomber).
Both Mitsubishi and Nakajima were asked to build two prototypes each, a further
proposal from Kawasaki being rejected. The Mitsubishi design was an all-metal
mid-wing cantilever monoplane with retractable landing gear, ventral bomb bay
and two radial engines. 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 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 (825 hp)
Mitsubishi Ha-6 radial engines for the Nakajima Ha-5 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.
Role
Bomber
Manufacturer
Mitsubishi
First flight
18 December 1936
Introduction
1938
Primary users
Japan
Thailand
Number built
2,064 units (excluding Ki-57)
Variants
Mitsubishi Ki-57
The Ki-21-Ia was used in combat in the war with China by the 60th Sentai from
autumn 1938, carrying out long-range unescorted bombing missions in conjunction
with the BR.20 equipped 12th and 98th Sentais. The Ki-21 proved to be more
successful than the BR.20, having a longer range and being more robust and
reliable. Two more Sentais, the 58th and 61st deployed to Manchuria in the
summer of 1939 for operations against China, with aircraft from the 61st also
being heavily used against Russian and Mongolian Forces during the Nomonhan
Losses were high during early combat operations, with weaknesses including a
lack of armament and self-sealing fuel tanks, while the aircraft's oxygen system
also proved unreliable. The Ki-21-Ib was an improved version designed to address
the armament issue by increasing the number of 7.7 mm (.303 in) Type 89 machine
guns to five, and incorporating improvements to the horizontal tail surfaces and
trailing edge flaps. In addition, the bomb bay was enlarged. The tail gun was a
'stinger' installation, and was remotely controlled. Also, the fuel tanks were
partially protected with laminated rubber sheets.
However, by the attack on Pearl Harbor and the start of the Pacific War,
improvements in Republic of China Air Force 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 1,118 kW (1,500 hp) 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 the JAAF's 5th, 14th and 62nd Air Groups, based in Taiwan,
attacked American targets at Aparri, Tuguegarao, Vigan and other targets in
Luzon on 8 December 1941. The 3rd, 12th, 60th and 98th Air Groups, based in
French Indochina, struck British and Australian targets in Thailand and Malaya,
bombing Alor Star, Sungai Petani and Butterworth under escort by Nakajima Ki-27
and Ki-43 fighters. However, starting from operations over Burma in December
1941 and early 1942, the Ki-21 began to suffer heavy casualties from Curtiss
P-40s and Hawker Hurricanes.
The Ki-21 had more than one Allied codename. Initially called "Jane", the name
was quickly changed to "Sally" when General Douglas MacArthur 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.
Specifications (Ki-21-IIb)
General characteristics
Crew: 5-7
Length: 16.0 m (52 ft 6 in)
Wingspan: 22.50 m (73 ft 10 in)
Height: 4.85 m (15 ft 11 in)
Empty weight: 6,070 kg (13,354 lb)
Loaded weight: 10,600 kg (23,320 lb)
radial engine, 1,119 kW (1,500 hp) each
Propellers: three-blade metal variable-pitch propellers propeller
Performance
Maximum speed: 485 km/h (301 mph) at 4,700 m (15,400 ft)
Cruise speed: 380 km/h (236 mph)
Range: 2,700 km (1,680 mi)
Service ceiling: 10,000 m (32,800 ft)
Rate of climb: 13 min 13 sec to 6,000 m (19,680 ft)
Armament
Guns:
tail positions
Bombs: 1,000 kg (2,200 lb) of bombs
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