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Mitsubishi G4M
Mitsubishi G4M1 of 801st Kokutai
Role Twin-engine medium bomber
Manufacturer Mitsubishi
Designed by Kiro Honjo
First flight 23 October 1939
Introduced June 1941
Retired 1945
Primary user Imperial Japanese Navy Air Service
Number built 2,435

The Mitsubishi G4M or ("Type 1 land-based attack aircraft")一式陸上攻撃機, 一式陸攻 Isshiki rikujō kōgeki ki, Isshikirikkō was the main twin-engine, land-based bomber used by the Imperial Japanese Navy Air Service in World War II. The Allies gave the G4M the identification name of Betty.[1]

Contents

Design and development

The G4M was designed for long range and high-speed at the time of its introduction. Consequently, weight saving measures were incorporated into the design, such as dispensing with self sealing fuel tanks, which caused Allied fighter pilots to give it the derisive nicknames "one-shot lighter", "flying Zippo" and "flying cigar". Similarly, pilots of the Imperial Japanese Navy called the G4M the "Type One Lighter" and "Hamaki" ("Cigar"). This was due to the fact that on many occasions, it was used for low-altitude torpedo attacks where its performance advantages were negated. The "Betty"'s relatively-large size made it a large target to shoot at, and the simplified approach path on a torpedo run to attack a ship, meant for a generally easy interception.

When used for medium- to high-altitude bombing against stationary targets like a supply depots, seaports, or airfields, "ease of interception" was another matter entirely. Using its long range and high speed, the G4M could appear from any direction, and then be gone before many fighters could intercept them. The 20 mm cannon in the tail turret was much heavier armament than commonly installed in bombers, making dead astern attacks very dangerous. Sometimes, assuming they did not catch fire in the first place, G4Ms also proved to be able to remain airborne despite being badly shot up. For example, after 751 Kokutai's attack during the Battle of Rennell Island, three out of four survivors (of 11 aircraft that went to attack) returned flying on one engine only. Near the end of the war, the "Betty" was used as a common kamikaze-carrying and launching platform, and was the usual aircraft for carrying the Ohka kamikaze rocket aircraft.

Production

  • Total production of G4M1 Model 11: 1172 examples including prototypes.
  • Total production of G4M2 Models 22, 22 Ko and 22 Otsu: 429 examples.
  • Total production of G4M2a, Models 24, 24 Ko, 24 Otsu, 24 Hei, and 24 Tei: 713 examples.
  • Total production of G4M3 Models 34 Ko, 34 Otsu, and 34 Hei: 91 examples.
  • Total production of G6M1: 30 examples.
  • Total production of all versions: 2,435 examples.

Operational history

721st Kokutai's G4M2e bomber carrying Ohka

The G4M was similar in performance and missions to other contemporary twin-engine bombers such as the German Junkers Ju 88 and Heinkel He 111, and the American B-25 Mitchell, and B-26 Marauder. These were all commonly used in the anti-shipping role. The G4M Model 11 was prominent in attacks on Allied shipping in the 1941 to early 1944 time-frame, but beyond that time, it was increasingly the easy prey of the ever-improving enemy fighters.

The G4M's baptism by fire occurred on 13 September 1940 in Mainland China, when 27 "Bettys" and Mitsubishi C5M1 of 1st Rengo Kokutai (a composite force including elements of Kanoya and Kizarazu Kokutais) departed from Taipei, Omura and Cheju to attack Hankow. The bombers and reconnaissance aircraft were escorted by 13 A6M Zeros of 12st Kokutai led by Navy Lieutenant Saburo Shindo. A similar operation occurred in May 1941. In December 1941, 120 Taiwan-based G4Ms of 1st Kokutai and Kanoya Kokutai belonging to the 21st Koku Sentai crossed the Luzon Strait en route to bombing the Philippines, the beginning to widespread Southeast Asia operations.

IJN aviators pressed home a torpedo attack against American ships off Guadalcanal on 8 August 1942, suffering heavy losses.

As torpedo bombers, the G4M's most notable use was in the sinking of Prince of Wales and Repulse off the coast of Malaya on 10 December 1941. They carried out the attacks alongside the older Japanese bombers, the Mitsubishi G3M "Nells" who were doing high-level bombing runs. The battleship Prince of Wales and battlecruiser Repulse were the first two capital ships ever to be sunk exclusively by air attack during a war, while at sea. Those bomber crews were a handful of selected Imperial Japanese Naval Air Force (IJNAF) aviators in prewar Japan, who had skills not only in torpedo-attacking at less than 9 m (30 ft) high but also in being able to navigate long-range flight over the ocean to spot a pinpoint target moving fast on the sea. The same squadrons in Kanoya Air Group (751 Ku), Genzan Air Group (753 Ku) and Mihoro Air Group (701 Ku), which sunk the British capital battle ships, later staged an extended series of attacks against American ships and land targets in Battle of Guadalcanal in the Solomon Islands, late 1942.

On 8 August 1942, the second day of US Marine's landing at Guadalcanal, IJNAF's 23 G4M1s conducted a torpedo attack against American ships at Lunga point, Guadalcanal. 18 of the attacking G4M1s were lost, due to extraordinarily heavy antiaircraft fire and air cover from F4F Wildcat fighters. In all, 18 Japanese crews of approximately 120 aviators were missing in the beginning of the months. Over 100 Japanese G4M1s and their best crews with no substitute were thoroughly lost in the following battles of Guadalcanal, from August-October 1942.[2] In two days of the Battle of Rennell Island on 29 and 30 January 1943, 10 out of 43 Japanese G4M1s were lost in the night torpedo-attacks, again to American anti-aircraft fire. About 70 Japanese aviators, including Lieutenant Commander Higai, were killed in action.

Crashed G4M1 floating at Tulagi.

Probably the best-known incident involving a G4M during the war was the attack resulting in the death of Isoroku Yamamoto. The G4M with tail number T1-323 - which was carrying the Imperial Japanese Navy Admiral Isoroku Yamamoto - was attacked and shot down by P-38 Lightnings on 18 April 1943.

The G4M Model 11 was replaced by Models 22,22a/b,24a/b,25,26 and 27 after June 1943, following service in New Guinea, the Solomons, and the South Pacific area, in defense of Marianas and finally in Okinawa, with field modifications resulting in the Model 24j which carried suicide flying bombs Yokosuka MXY7 Ohka Model 11 beginning on 21 March 1945, with disastrous results due to heavy Allied fighter opposition.

Following the loss of Okinawa, G4Ms constituted the main weapon of the land-based Japanese naval bomber force, consisting of 20 Kokutais when at war's end, including the testing air group equipped in 1944-45 with the latest version G4M3 Model 34 and 36, arriving too late to change the course of the war.

As part of the negotiations for the surrender of Japan, two demilitarized G4Ms, given the call-signs Bataan 1 and Bataan 2 were sent to Ie Shima carrying the first surrender delegations as the first leg of their flight to Manila.

In 1945, Indonesian guerrillas captured numerous ex-Japanese air bases including Bugis Air Base in Malang (repatriated 18 September 1945). Several G4Ms were seized and flown by the Indonesians. Most of the aircraft were destroyed during 1945–1949 when the former Dutch East Indies and the Netherlands were engaged in a military conflict in Indonesia.

Versions

An early-production Mitsubishi G4M1 Model 11 without the propeller spinners

G4M1

G4M1 Prototypes
Japanese Navy land Based Bomber Type 1. Two prototypes built.
G4M1 Model 11
Japanese Navy Land Attack Bomber Type 1. The first bomber model of series, with 1,140 kW (1,530 hp) Mitsubishi MK4A Kasei Model 11 engines driving three-blade propellers. Following modifications were made during the production:
  • March 1942:The first aircraft (241st production example) fitted with MK4E Kasei Model 15 engines with larger superchargers for better high altitude performance, became standard in August 1942 from 406th aircraft onwards. These MK4E-engined aircraft have been often, erroneously, referred as the G4M1 Model 12.
  • Summer 1942:Propeller spinners introduced.
  • March 1943:From 663rd machine onwards, 30 mm (1.18 in) rubber ply sheets installed beneath the wing outer surfaces to protect the undersides of the fuel tanks (speed reduced by 9 km/h/6 mph and range by 315 km/196 mi), 5 mm (.2 in) armour plates added into tail gunner's compartment.
  • Spring 1943:Outer half of the tail cone cut away in order to improve tail gunner's field of fire.
  • August 1943:A completely redesigned tail cone, with reduced framing and wide V-shaped cut out; this form of tail cone was also used in all G4M2 models.
  • September 1943:Individual exhaust stacks from 954th airframe onwards.

Production of the G4M1 ended in January 1944.

G4M2

The first of the four G4M2 prototypes flew in December 1942. It differed from the preceding model in having MK4P Kasei Model 21 engines with VDM Electric four-blades capable of full feathering function, re-designed main wings with LB type laminar flow airfoil[3] and widened tail horizontal stabilizer wing area, which improved service ceiling to 8,950 m (29,360 ft) and maximum speed to 437 km/h (236 kn, 272 mph). Main wing fuel tanks were enlarged to 6,490 L (1,715 US gal) which enabled range of 6,100 km (3,790 mi/ 3,294 nmi overloaded, one way). An electrically-powered dorsal turret featuring a 20 mm cannon was introduced in place of G4M1's dorsal position with a 7.7 mm machine gun, total guns armed were 2 × 20 mm Type 99 cannon (1 × tail turret, 1 × top turret), 4 × 7.7 mm Type 92 machine gun (1 × nose, 2 × waist, 1 × cockpit side). External differences also included increased nose glazing, flush side gun positions instead of blisters, and rounded tips of wings and tail surfaces. These major improvements also made G4M2 possible to carry more powerful bombs; 1 × 1,055 kg (2,326 lb) Type 91 Kai-7 (improved model 7) aerial torpedo or 1 × 800 kg (1,760 lb) bomb or 2 × 500 kg (1,100 lb) bombs or 1 Type 3 - 800 kg (1,760 lb) no.31 ray-detective type bomb + 12 × 60 kg (130 lb) bombs. This model G4M2 was into service in mid-1943.

G4M2e Model 24 Tei launching suicide bomb Yokosuka MXY-7 Ohka "Baka"
Betty bombers during an air raid over Darwin, Australia..
G4M2 Model 22
The base model, the first production example completed in July 1943. Introduced bulged bomb bay doors from 65th aircraft onwards, and an optically flat panel in the nose cone from the 105th aircraft onwards.
G4M2 Model 22Ko
Very similar to previous model. Carried Type 3 Ku Mark 6 search radar and was armed with two 20 mm Type 99 Mark 1 cannons replacing the 7.7 mm machine guns in the lateral positions.
G4M2 Model 22 Otsu
Dorsal turret cannon changed to longer-barreled 20 mm Type 99 Mark 2.
G4M2a Model 24
Modified Model 22, MK4T Kasei 25 1,340 kW (1,800 hp) engines, with bulged bomb bay doors as standard for larger bomb capacity. Externally distinguishable from the Model 22 by a carburetor air intake on the top of the engine cowling.
G4M2a Model 24 Ko/Otsu
Armament similar to Model 22 Ko/Otsu respectively.
G4M2a Model 24 Hei
Modified 24 Otsu, with one 13.2 mm (.51 in) Type 2 machine gun mounted in tip of the nose cone, radar antenna relocated from that position to above the nose cone.
G4M2b Model 25
One G4M2a modified to MK4T-B Kasei 25 Otsu 1,360 kW (1,825 hp) engines. Only experimental.
G4M2c Model 26
Two G4M2a modified to MK4T-B Ru Kasei 25b 1,360 kW (1,825 hp) engines with turbochargers.
G4M2d Model 27
One G4M2 modified to MK4V Kasei 27 1,340 kW (1,800 hp) engines.
G4M2e Model 24 Tei
Special version for the transport of the ramming attack bomb plane Kugisho/Yokosuka MXY-7 Ohka ("Baka") Model 11, conversions of G4M2a Models 24 Otsu and 24 Hei. Had armour protection for the pilots and fuselage fuel tanks.
MXY11 Yokosuka Navy Type 1 Attack Bomber
Ground Decoy Non-flying replica of Mitsubishi G4M2 developed by Yokosuka

G4M3

Mid- or late-production G4M1 Model 11s with the propeller spinners and rubber ply beneath the wing fuel tanks.
Early production G4M1s of Kanoya Kokutai with the original shape tail cones.
G4M3 Model 34
Redesigned G4M2 with added self-sealing fuel tanks, improved armor protection and an entirely new tail gunner's compartment which was quite similar to that of late model B-26 Marauders. Wings were also redesigned and horizontal tail plane was given dihedral. Armed with 2 × 7.7 mm Type 92 machine guns in nose cabin and in both side positions, and 1 × 20 mm Type 99 Model 1 cannon in dorsal turret and tail. Entered production in October 1944 in G4M3a Model 34 Ko form with 20 mm cannon in side positions instead of machine guns.
G4M3a Model 34 Otsu and Hei
Similar modifications as in corresponding Model 24 variants.
G4M3 Model 36
Prototype. Two G4M2 Model 34 modified to Mitsubishi MK4-T Kasei 25b Ru 1,360 kW (1,825 hp) engines.

G6M1

G6M1 Japanese Navy Long Range Heavy Fighter Type 1
Initial model of the series, armed with 20 mm Type 99 cannons between each side of fuselage and in tail, 1 × 7.7 mm machine gun in nose cabin and 1 × 30 mm cannon in front ventral position. 30 built.
G6M1-K Trainer, Japanese Navy Type 1
Converted G6M1s.
G6M1-L2 Transport Type 1, Japanese Navy
Modified as transports.

Operators

 Indonesia
  • After the Japanese surrender in 1945, the Indonesian People's Security Force (IPSF) (pro-independence guerrillas) captured a small number of aircraft at Japanese air bases. Most aircraft were destroyed in combat with the Dutch forces during the Indonesian National Revolution of 1945–1949.
 Japan
 United Kingdom
  • Royal Air Force operated at least one captured aircraft for evaluation purposes.
 United States

Specifications (G4M1, Model 11)

Data from Airreview's Japanese Navy Aircraft In The Pacific War.[5]

General characteristics

  • Crew: 7 (main-pilot, co-pilot, navigator/bombardier/nose gunner, captain/top turret gunner, radio operator/waist gunner, engine mechanic/waist gunner, tail gunner)
  • Length: 19.97 m (65 ft 6¼ in)
  • Wingspan: 24.89 m (81 ft 7¾ in)
  • Height: 4.9 m (16 ft 1 in (in a horizontal position))
  • Wing area: 78.13 m² (840.9 ft²)
  • Airfoil: Mitsubishi type
  • Empty weight: 6,741 kg (14,860 lb)
  • Loaded weight: 9,500 kg (20,944 lb)
  • Max takeoff weight: 12,860 kg (28,350 lb)
  • Powerplant: 2× Mitsubishi "Kasei (Fire star)" Type 11, 14 cylinder radial engines, 1,141 kW (1,530 hp) each
  • Propellers: 4-bladed Hamilton licensed Sumitomo constant speed variable-pitch

Performance

Armament

  • Guns: 1 × 20 mm Type 99 cannon (tail turret), 4 × 7.7 mm Type 92 machine gun (nose turret × 1, waist turret × 2, top turret × 1)
  • Bombs: 1 × 858 kg (1,892 lb) Type 91 Kai-3 (improved model 3) aerial torpedo or 1 × 800 kg (1,764 lb) bomb or 4 × 250 kg (551 lb) bombs

See also

Related development

Comparable aircraft

References

Notes
  1. ^ The Allies usually gave Japanese fighters and floatplanes "male" names, while giving "female" names to bombers and reconnaissance aircraft. These did not come into general use until mid-1943.
  2. ^ Fumio, Iwaya. Chuko (Medium Attack Bomber). Tokyo: Hara Shobo, 1958.
  3. ^ LB type laminar airfoil: designed by Prof. Tani of Tokyo Univ. in 1937
  4. ^ Captured USAAF Mitsubishi G4M Betty
  5. ^ Aoki, Hideo. "Mitsubishi Type 1 Attack Bomber (G4M) Betty." Airreview's Japanese Navy Aircraft In The Pacific War, Kantosha, 1972, pp. 128–136.
  6. ^ Serial no. 603 and later had 30 mm (1.2 in) thick natural rubber plates covered their outside bottoms of wing fuel tanks but lost their service range by 10 % instead.
Bibliography
  • Aoki, Hideo. "Kugisho Suicide Attacker "Oka" (MXY7) Baka." Airreview's Japanese Navy Aircraft In The Pacific War, Kantosha, 1972.
  • Bridgwater, H.C. and Peter Scott. Combat Colours Number 4: Pearl Harbor and Beyond, December 1941 to May 1942. Luton, Bedfordshire, UK: Guideline Publications, 2001. ISBN 0-9539040-6-7.
  • Chant, Chris. Aircraft Of World War Two. London: Grange Books PLC. 2001. ISBN 1-84084-329-2.
  • Ferkl, Martin. Mitsubishi G4M Betty (in English). Praha, Czech Republic: Revi Publications, 2002. ISBN 80-85957-09-4.
  • Francillon, René J. Imperial Japanese Navy Bombers of World War Two. Windsor, Berkshire, UK: Hylton Lacy Publishers Ltd., 1969. ISBN 0-85064-022-9.
  • Francillon, René J. Japanese Aircraft of the Pacific War. London: Putnam & Company Ltd., 1979. ISBN 0-370-30251-6.
  • Francillon, René J. Mitsubishi G4M "Betty" & Okha Bomb (Aircraft in Profile 210). Windsor, Bershire, UK: Profile Publications Ltd., 1971.
  • Green, William. Famous Bombers of the Second World War. London: Macdonald and Jane's Publishers Ltd., 1975. ISBN 0-356-08333-0. (2nd edition of 1959 book, reprinted at least twice: 1976 and 1977)
  • Gunston, Bill. The Illustrated Encyclopedia of Combat Aircraft of World War II. London, UK: Salamander Books Ltd., 1979. ISBN 0-89673-000-X (3rd "impression", 1979; Library of Congress Catalogue No. 77-95252)
  • Horodyski, Joseph M. "British Gamble In Asian Waters". Military Heritage. December 2001. Volume 3, No. 3: pp. 68–77 (sinking of the British battleship Prince of Wales and battlecruiser Repulse by Japanese on 10 December 1941 upon U.S. entry into World War Two).
  • Morgan, Eric B. "Mitsubishi G4M Betty" Twentyfirst Profile Vol.2, No.17. New Milton, Hantfordshire, UK: 21st Profile Ltd., ISBN 0-961-8120-11.
  • Nowicki, Jacek. Mitsubishi G4M "Betty" (in Polish). Warszawa, Poland: Wydawnictwo Militaria, 1998. ISBN 83-7219-020-8.
  • Tagaya, Osamu. Mitsubishi Type 1 Rikko Betty Units of World War 2 London, UK: Osprey Publishing, 2001. ISBN 1-84176-082-X.
  • Thorpe, Donald W. Japanese Naval Air Force Camouflage and Markings World War II. Fallbrook, California; Aero Publishers Inc., 1977. ISBN 0-8168-6587-6. (pbk.) ISBN 0-8168-6583-3. (hc.)

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