In response to a 1935 Japanese naval requirement for a landbased twin-engine reconnaissance aircraft, Mitsubishi flew the first Ka-15 prototype, an aircraft which possessed a design potential that allowed development as a long-range medium bomber. Following successful flight trials, the aircraft entered production in June 1936 as the Navy Type 96 Attack Bomber Model 11 (Mitsubishi G3M1).
In its original prototype form the Ka 15, designed by Kiro Honjo, made its first flight in July 1935. Two 750 hp Hiro Type 91 12-cylinder V type engines were mounted on the mid set wings, which were essentially the same as those of the Ka 9.
Twenty more prototype/preproduction Ka 15s were completed, of which three had Hiro engines; the remaining 17 were powered by 830 hp or 910-hp Mitsubishi Kinsei 2 or 3 14 cylinder two-row radial engines, giving enhanced performance. These aircraft had the designation G3M1, and unofficially they were subdivided into G3M1a (the four with Hiro engines and solid noses), G3M1b (two with Kinseis and solid noses), and G3M1c (the other 15 Kinsei powered aircraft, which had a transparent bombing station in the nose). Twelve were used for service trials, but before these had been completed a production batch of 34 Kinsei 3 powered G3M1s, with modified cockpit windows, was authorized by the IJN. These had a crew of five, and could carry an 800 kg (1763 1b) torpedo beneath the fuselage; defensive armament consisted of two retractable dorsal turrets each containing one 7.7 mm (0.303 in) Type 92 machine gun, with another of these guns in a retractable ventral turret.
As the improved Kinsei 41 and 42 engine became available in 1937 a new version, the G3M2, started production and, with a total of 581 built by mid-1941, was the principal variant. With a top speed now increased to 374km/h, a bombload of up to 800kg carried externally and a defensive armament of three 7.7mm machine-guns, the G3M2 possessed a maximum range of 4380km.
It was built in two basic variants, the Model 21 and Model 22. The 21 had uprated Kinsei 41 or 42 engines of 1075 hp, increased fuel tankage and modified dorsal turrets; the 22 had 1075 hp Kinsei 45s (also fitted to some late¬production Model 21s), and a completely revised armament system that eliminated the retractable ventral and rear dorsal turrets, replacing the latter by a large turtleback enclosure housing a 20 mm (0.79 in) Type 99 cannon, and the former by a pair of blisters, one each side of the rear fuselage, each with single Type 92 gun. Between 1937 39, Mitsubishi built 343 Model 21s, following these in 1939 41 with 238 Model 22s.
Mitsubishi G3M2s were first flown in action by the Japanese navy’s Kanoya Kokutai in August 1937 in raids on Hangchow and Kwangteh in China. By 1940 four kokutais in China were equipped with a total of about 130 G3M2s, a number that grew to 204 by the date of Pearl Harbor with the deployment of forces against Wake Island, the Philippines and the Marianas. And it was a force of 60 G3M2s of the Genzan and Minoro Kokutais (with 26 Mitsubishi G4Mls of the Kanoya Kokutai) which, flying from bases in Indo-China, found and sank the British warships HMS Prince of Wales and HMS Repulse as they steamed without fighter protection off the Malayan coast on 10 December 1941. The type was known to the Allies as the ‘Nell’.
When Mitsubishi production was then phased out in favour of the later G4M bomber, production of the G3M was carried on by the Koizumi factory of the Nakajima company, which built 412 G3M type bom-bers, of which a proportion were of a fourth model, the G3M3. These had Kinsei 51 radials of 1300 hp each, and a further increase in fuel tankage, extending the max¬imum range to 6230 km (3870 miles) com-pared with the 4380 km, (2720 miles) of the G3M2 Model 22.
At the time of Pearl Harbor, the backbone of Japan’s long range strike force consisted of just over 200 G3Ms (mostly G3M2s and G3M3s) and about 120 of the later G4M1s. The G3M (‘Nell’ under the Pacific system of codenarnes introduced by the Allies during the Second World War) had made its service debut in August 1937, with raids on Chinese mainland targets from bases on Kyushu (Omura) and Formosa (Taipei).
The G3M was used throughout the war, in most of the Pacific theatres, as was the G3M1 L, a prewar transport conversion with Kinsei 45 engines which took part in the invasion of Celebes. Wartime transport con¬versions were the L3Y1 Model 11 and L3Y2 Model 12 (both codenarned ‘Tina’), con¬verted from G3M1s and G3M2s respectively by the First Naval Air Arsenal at Kasurnigaura. These carried up to ten pas¬sengers, and had a single 7.7 mm (0.303 in) machine gun for defence.
Total production of the G3M series reached 1100, including the Kinsei 42 powered G3M2b, the transport G3M2d (L3Y2) and the G3M3 final bomber.
G3M 1
Engines: 2 x 678kW Kinsei 3
Maximum speed: 360km/h at 1975m
G3M2
Engines: 2 x Mitsubihi Kinsei 45, 1000 hp
Wingspan: 82 ft 0.25 in
Length: 53 ft 11.75 in
Height: 11 ft 11.75 in
Empty weight: 11,442 lb
Loaded weight: 17,637 lb
Max speed: 238 mph at 9,840 ft
Service ceiling: 29,890 ft
Amament: 1 x 20mm cannon, 2 x 7.7mm mg
Bombload: 2200 lb or 1 x 1760 lb torpedo
Crew: 7
G3M2 Model 22
Span: 25m (82ft 0.25in)
Length. 16.45 m (53 ft 11.75 in)
Gross weight: 8000 kg (176371b)
Maximum speed: 373 km/h (232 mph)
G3M3
Engines: 2 x Mitsubishi MK8 Kinsei-51, 975kW
Max take-off weight: 8000 kg / 17637 lb
Empty weight: 5250 kg / 11574 lb
Wingspan: 25.0 m / 82 ft 0 in
Length: 16.5 m / 54 ft 2 in
Height: 3.7 m / 12 ft 2 in
Wing area: 75.1 sq.m / 808.37 sq ft
Max. speed: 415 km/h / 258 mph at 6000m
Cruise speed: 295 km/h / 183 mph
Ceiling: 10300 m / 33800 ft
Range w/max.fuel: 6200 km / 3853 miles
Armament: 1 x 20mm cannon, 4 x 7.7mm machine-guns, 800kg of bombs
Crew: 5
All Aero 