The Mitsubishi G4M is a twin-engine, land-based medium bomber formerly manufactured by the Mitsubishi Aircraft Company, a part of Mitsubishi Heavy Industries, and operated by the Imperial Japanese Navy from 1940 to 1945. Its official designation is and was commonly referred to by Japanese Navy pilots as due to the cylindrical shape of its fuselage and its tendency to ignite after a hit. The Allied reporting name was "Betty".
Designed to a strict specification to succeed the Mitsubishi G3M already in service, the G4M boasted very good performance and excellent range and was considered the best land-based naval bomber at the time. This was achieved by its structural lightness and an almost total lack of protection for the crew, with no armor plating or self-sealing fuel tanks.[1] The G4M was officially adopted on 2 April 1941 but the aforementioned problems would prove to be a severe drawback, often suffering heavy losses; Allied fighter pilots nicknamed the G4M "The Flying Lighter" as it was extremely prone to ignition after a few hits.[1] It was not until later variants of the G4M2 and G4M3 that self-sealing fuel tanks, armor protection for the crew and better defensive armament was installed.
Nevertheless, the G4M would become the Navy's primary land-based bomber. It is the most widely produced and most famous bomber operated by the Japanese during World War II and it served in nearly all battles during the Pacific War.[1] Attacks by G4M and G3M bombers resulted in the sinking of the Royal Navy battleship and battlecruiser, the first time capital ships actively defending themselves were sunk solely by air power while in the open sea. G4Ms and G3Ms are also credited with sinking the heavy cruiser USS Chicago during the Battle of Rennell Island. The aircraft later served as the mothership that carried the Yokosuka MXY-7 Ohka, a purpose-built anti-ship suicide weapon during the final years of the war.[2] Of the 2,435 G4Ms produced, no fully intact aircraft have survived, though several airframes exist as unrestored wreckage or in partial states of completion.
The G4M's predecessor, the Mitsubishi G3M, went into service in 1937 in China.[3] Only two months later the Japanese Navy issued specifications to Mitsubishi.[3] The specifications, unprecedented at the time, called for a twin-engine, land-based, attack bomber with a top speed of 398km/h, a cruising altitude of 3000m (10,000feet), and a range of 4722km (2,934miles) unloaded (without bombs and torpedoes), and a range of 3700km (2,300miles) when carrying an 800kg (1,800lb) torpedo or the same weight in bombs.[3]
The G4M was designed for a long range and high speed at the time of its introduction. In order to meet the Navy's specifications a Mitsubishi team led by Kiro Honjo did not incorporate self-sealing fuel tanks and armor plating to save weight and extend range.[3] This consequently made both the G4M and the Zero, in which Mitsubishi used the same design features, vulnerable to machine gun and cannon fire.[3] Consequently, this led to Allied fighter pilots giving it derisive nicknames such as "the flying lighter"[3] "the one-shot lighter", "the flying Zippo" and "the flying cigar" because of its tendency to ignite from damage to the wing fuel tanks after being hit by gunfire. The pilots of the Imperial Japanese Navy called the G4M the "hamaki" ("cigar"), although this was due to its shape.[3] Due to deficiencies of the G3M in warding off concentrated fighter attacks Honjo incorporated 7.7mm guns in the nose, on top and both sides of the fuselage and in the tail a 20mm cannon was added.[3]
When used for medium- to high-altitude bombing against stationary land targets like supply depots, seaports or airfields, it was much harder to intercept. Using its long range and high speed, the G4M could appear from any direction, and leave before any fighters intercepted it. The 20 mm cannon in its tail turret was much heavier armament than was commonly carried by bombers of either side, making aerial attacks from the rear quite dangerous for the Allied fighter aircraft. If G4Ms did not catch fire after being hit in the wings by flak from the ground or by machine gun bullets from enemy fighters, they could remain airborne despite severe damage. For example, after the attack of the 751 Kōkūtai (air group) on the USS Chicago during the Battle of Rennell Island, three out of four surviving aircraft (of the original eleven) returned despite flying with only one engine.
As the war continued improved bomber designs failed to materialize and Mitsubishi began creating additional versions to fulfill various new missions as well as eliminate the weakness in the design including various engine and weapon variants. The G4M2 redesign failed to rectify the G4M's vulnerability to weapons fire.[3]
The first G4M prototype left Mitsubishi's Nagoya plant in September 1939 disassembled and loaded in five ox-drawn farm carts to Kagamigahara airfield 48km (30miles) to the north.[3] On 23 October 1939, test pilot Katsuzo Shima flew the G4M prototype.[3] Despite successful tests the Navy shelved the bomber for the more heavily armed G6M1 variant in hopes it could be used as heavy escort fighter for other bombers. Failing these expectations the G4M1 was ordered into production.[3]
The first production G4M was completed in April 1941 and was not discontinued until the end of the war.[3]
The G4M was similar in performance and missions to other contemporary twin-engine bombers such as the German Heinkel He 111 and the American North American B-25 Mitchell. These were all commonly used in anti-ship roles. The G4M Model 11 was prominent in attacks on Allied shipping from 1941 to early 1944, but after that it became increasingly easy prey for Allied fighters.
The G4M was first used in combat on 13 September 1940 in Mainland China, when 27 "Bettys" and Mitsubishi C5Ms of 1st Rengo Kōkūtai (a mixed force including elements of the Kanoya and Kizarazu Kōkūtai) departed from Taipei, Omura, and Jeju City to attack Hankow. The bombers and the reconnaissance aircraft were escorted by 13 A6M Zeros of 12th Kōkūtai led by the IJN lieutenant, Saburo Shindo. A similar operation occurred in May 1941. In December 1941, 107 G4Ms based on Formosa of 1st Kōkūtai and Kanoya Kōkūtai belonging to the 21st Koku Sentai (air flotilla) crossed the Luzon Strait en route to bombing the Philippines; this was the beginning of Japanese invasions in the Southwest Pacific Theater.
In its first year of combat the G4M was a success. They bombed the U.S. Army air base Clark Field, Philippines on 8 December 1941. The G4M was instrumental in sinking HMS Prince of Wales and HMS Repulse two days later. Nine G4Ms participated in the long-range bombing raid of Katherine, Northern Territory, on 22 March 1942 (the deepest inland attack on Australian territory during the war at over 200 miles from the coast). Against weak fighter opposition the G4M attacked targets ranging as far as the Aleutians to Australia using its long range, the drawbacks of no self-sealing fuel tanks and armor not presenting themselves as problems at this point.[3]
The G4M's most notable use as a torpedo bomber was in the sinking of Prince of Wales and Repulse off the eastern coast of Malaya on 10 December 1941. The G4Ms attacked along with older Mitsubishi G3M "Nell" bombers, which made high-level bombing runs. Prince of Wales and Repulse were the first two capital ships to be sunk exclusively by air attacks during a war, while in open waters. The bomber crews were from the Kanoya Air Group (later 751 Ku), Genzan Air Group (later 753 Ku), and the Mihoro Air Group (later 701 Ku), trained in torpedo attacks at an altitude of less than 10m (30feet), and in long-range over-ocean navigation, so they could attack naval targets moving quickly at sea.
G4Ms later made many attacks against Allied ships and also land targets during the six-month-long Guadalcanal Campaign (in the Solomon Islands) in late 1942. More than 100 G4M1s and their pilots and crews were lost (with no replacements or substitutes available) during the many battles over and near Guadalcanal from August to October 1942. On 8 August 1942, during the second day of the U.S. Marine landings on Guadalcanal, 23 IJNAF torpedo-carrying G4M1s attacked American ships at Lunga Point, but 18 of the G4M1s were shot down, by very heavy anti-aircraft fire and carrier-based F4F fighters. In all 18 Japanese crews – approximately 120 aviators – were lost at Lunga Point. In the two days of the Battle of Rennell Island, 29 and 30 January 1943, 10 out of 43 G4M1s were shot down during night torpedo attacks, all by U.S. Navy anti-aircraft fire. About 70 Japanese aviators, including Lieutenant Commander Higai, were killed during that battle.
Probably the best-known incident involving a G4M during the war was the attack resulting in the death of Admiral Yamamoto. On 18 April 1943, sixteen P-38 Lightnings of the 339th Fighter Squadron of the 347th Fighter Group, Thirteenth Air Force, shot down a G4M1 of the 705th Kōkūtai with the tailcode T1-323, carrying Admiral Yamamoto. In the same battle, another G4M1 carrying Chief of Staff Vice Admiral Matome Ugaki was also downed by the P-38s, although Ugaki survived.[4]
The G4M Model 11 was replaced by the Models 22, 22a/b, 24a/b, 25, 26, and 27 from June 1943 onward, giving service in New Guinea, the Solomons, and the South Pacific area, in defense of the Marianas and finally in Okinawa. Other G4Ms received field modifications, resulting in the Model 24j. This model carried the Yokosuka MXY7 Ohka Model 11 suicide flying bomb, beginning on 21 March 1945, with disastrous results due to heavy Allied fighter opposition.
After the loss of Okinawa, G4Ms constituted the main weapon of the land-based Japanese naval bomber force. It consisted of 20 Kōkūtai at the end of the war. This included the testing air group, which was equipped in 1944–45 with the latest version G4M3 Models 34 and 36, though these arrived too late to affect the course of the war.
From November 1944 to January 1945, G4Ms were one of the main types of aircraft used in the Japanese air attacks on the Mariana Islands, and plans to use converted G4Ms to land commandos on the islands were developed in mid-1945 and cancelled only at the end 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, flew to Ie Shima, carrying the first surrender delegations on the first leg of their flight to Manila. The G4Ms were painted white with green crosses, and were escorted by American P-38 fighters.[5]
The G4M's intended successor was the Yokosuka P1Y Ginga, although because of production problems, the changeover was only begun by the time the war ended.
Production of the G4M1 ended in January 1944.
The first of the four G4M2 prototypes flew in December 1942 (Mitsubishi Navy Type 1 Attack Bomber Model 22). It differed from the preceding model in having Mitsubishi MK4P "Kasei" Model 21 engines with VDM electric four-blade propellers capable of full feathering function, redesigned main wings with LB type laminar flow airfoil. and widened tail horizontal stabilizer wing area, which improved service ceiling to 8950m (29,360feet) and maximum speed to 437kph. Main wing fuel tanks were enlarged to 6490L which increased the range to 6000km (4,000miles) (overloaded, one way). An electrically powered dorsal turret featuring a 20abbr=onNaNabbr=on Type 99 cannon was introduced in place of G4M1's dorsal position with a 7.7abbr=onNaNabbr=on Type 92 machine gun, total guns armed were two 20abbr=onNaNabbr=on Type 99 cannons (one tail turret, one top turret), and four 7.7abbr=onNaNabbr=on Type 92 machine guns (one nose, two waist, and one 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 it possible for the G4M2 to carry more powerful bombs; one 1055kg (2,326lb) Navy Type 91 Kai-7 aerial torpedo or one 800kg (1,800lb) bomb or two 500kg (1,100lb) bombs or one 800kg (1,800lb) Type 3 No. 31 bomb (ray-detective type bomb) and twelve 60kg (130lb) bombs. The G4M2 entered service in mid-1943.
No complete or flyable Mitsubishi G4Ms are left, although several wrecks remain scattered in southeast Asia and on Pacific islands, having been left in-situ following the end of the war.[7] In addition, several G4Ms survive in the form of preserved fuselage sections.
Several other locations display pieces of G4Ms including the restored fuselage of a G4M2 is on display at the Kawaguchiko Motor Museum in Yamanashi Prefecture, Japan.[13]
Additionally the Smithsonian Institution retains the forward fuselage of a G4M3 Betty Model 34. Likely based in Oppama Air Field near Yokosuka, Japan there is no recorded tail number. The aircraft was part of 145 other Japanese aircraft for tests and evaluations by the U.S. Navy. After being flight tested as "Foreign Equipment Test number T2-2205" the airplane was dismembered by a cutting torch for unknown reasons.[14]
The wreck of Admiral Yamamoto's G4M1 Model 11 (Serial #2656) tail code 323 were still present at the crash site in the jungle near Panguna, Bougainville Island, with some parts and artifacts recovered and displayed at the museums in Papua New Guinea, Australia, and Japan. The wreck consisted of rear fuselage section and vertical stabilizer along with parts of the wings and engines. The crash site is accessible via prior arrangement to the landowners.[15] [16]
United States