Warplanes of Japan: Mitsubishi G4M

Mitsubishi G4M

(IJAAF Photo)

Early production G4M1s of Kanoya Kōkūtai with the original shape tail cones.

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 ImperialJapanese Navy from 1940 to 1945. Its official designation is Mitsubishi NavyType 1 attack bomber (一式陸上攻撃機, 一式陸攻,Ichishiki rikujō kōgeki ki, Isshikirikukō) and was commonly referred to byJapanese Navy pilots as Hamaki (葉巻,"cigar", lit. "leaf roll") 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 inservice, the G4M boasted very good performance and excellent range and wasconsidered the best land-based naval bomber at the time.[2] This was achievedby its structural lightness and an almost total lack of protection for thecrew, with no armor plating or self-sealing fuel tanks.[3] The G4M wasofficially adopted on 2 April 1941 but the aforementioned problems would proveto be a severe drawback, often suffering heavy losses; Allied fighter pilotsnicknamed the G4M "The Flying Lighter" as it was extremely prone toignition after a few hits. It was not until later variants of the G4M2 and G4M3that self-sealing fuel tanks, armor protection for the crew and betterdefensive armament was installed.

Nevertheless, the G4M would become the Navy's primary land-based bomber. It isthe most widely produced and most famous bomber operated by the Japanese during the Second World War and it served in nearly all battles during the Pacific War. Attacks by G4M and G3M bombers resulted in the sinking of the Royal Navy battleship HMS Prince of Wales and battlecruiser HMS Repulse, the first time capital ships actively defending themselves were sunk solely by air power while in the open sea.

(Royal Navy Photo)

HMS Repulse in the Atlantic, 30 Oct 1926.

(IWM Photo A 3869)

HMS Prince of Wales, c1941.

(USN Photo, NH715)

The US Navy heavy cruiser USS Chicago (CA-29) underway off New York City, during the 31 May 1934 fleet review.

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-shipsuicide weapon during the final years of the war. 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. Only two months later the Japanese Navy issued specifications to Mitsubishi. The specifications, unprecedented at the time, called for a twin-engine, land-based, attack bomber with a top speed of 398 kilometres per hour (247 mph), a cruising altitude of 3,000 metres (9,800 ft), and a range of 4,722 kilometres (2,934 mi) unloaded (without bombs and torpedoes), and a range of 3,700 kilometres (2,300 mi) when carrying an 800 kilograms (1,800 lb) torpedo or the same weight in bombs.

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 armourplating to save weight and extend range. This consequently made both the G4M and the Zero, in which Mitsubishi used the same design features, vulnerable to machine gun and cannon fire. Consequently, this led to Allied fighter pilots giving it derisive nicknames such as "the flying lighter", "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. Due to deficiencies of the G3M in warding off concentrated fighter attacks Honjo incorporated 7.7 mm (0.30 in) guns in the nose, on the top and both sides of the fuselage. A 20 mm (0.79 in) cannon was added in the tail.

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 tailt urret was a much heavier armament than was commonly carried by bombers of either side, making aerial attacks from the rear quite dangerous for 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.

The first G4M prototype left Mitsubishi's Nagoya plant in September 1939 disassembled and loaded in five ox-drawn farm carts to Kagamigahara airfield 48 kilometres (30 mi) to the north. On 23 October 1939, test pilot Katsuzo Shima flew the G4M prototype. Despite successful tests the Navy shelved the bomber for the more heavily armed G6M1 variant in hopes it could be used as a heavy escort fighter for other bombers. Failing these expectations the G4M1 was ordered into production.

The first production G4M was completed in April 1941 and was not discontinued until the end of the war.

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

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 at 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 thewar 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 longrange, the drawbacks of no self-sealing fuel tanks and armor not presenting themselves as problems at this point.

The G4M's most notable use as a torpedo bomber was in the sinking of HMS Prince of Wales and HMS 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. HMS Prince of Wales and HMS 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 10 metres (30 ft), 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 the American ships were well-defended by carrier-based F4F fighters and very heavy anti-aircraft fire. 18 of the G4M1s were shot down while 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.

(National Diet Library Photo)

Portrait of Yamamoto Isoroku (1884 – 1943) during his time as Commander-in-Chief of the Combined Fleet of the Imperial Japanese Navy.

Probably the best-known incident involving a G4M in the war came during the top secret mission to intercept the aircraft carrying Japanese Admiral Isoroku Yamamoto, resulting in Yamamoto's death.

(USAAF Photo)

Lockheed P-38G Lightnings were the aircraft chosen to carry out the mission.

On 18 April 1943, sixteen P-38G 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.

The G4M Model 11 was replaced by the Models 22, 22a/b, 24a/b, 25, 26, and 27from June 1943 onward, giving service in New Guinea, the Solomons, and theSouth Pacific area, in defense of the Marianas and finally in Okinawa. OtherG4Ms received field modifications, resulting in the Model 24j. This model carriedthe Yokosuka MXY7 Ohka Model 11 suicide flying bomb, beginning on 21 March1945, with disastrous results due to heavy Allied fighter opposition.

After the loss of Okinawa, G4Ms constituted the main weapon of the land-basedJapanese 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 thelatest version G4M3 Models 34 and 36, though these arrived too late to affectthe course of the war.

From November 1944 to January 1945, G4Ms were one of the main types of aircraftused in the Japanese air attacks on the Mariana Islands, and plans to useconverted G4Ms to land commandos on the islands were developed in mid-1945 andcancelled 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 thefirst surrender delegations on the first leg of their flight to Manila. TheG4Ms were painted white with green crosses, and were escorted by American P-38fighters.

The G4M's intended successor was the Yokosuka P1Y Ginga, although because ofproduction problems, the changeover was only begun by the time the war ended.(Wikipedia)

 (USN Photo)

IJNAF aviators flying Mitsubishi G4M codenamed "Betty" bombers pressing home a torpedo attack against American ships off Guadalcanal with heavy losses, on 8 August 1942.

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(IJAAF Photos)

Mitsubishi G4M.

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 (IJNAF Photos)

Mitsubishi G4M codenamed Betty in IJNAF service

Mitsubishi G4M bombers at Yokosuka Naval Air Depot, 1945 after occupation by US Navy.  (USN Photos)

Mitsubishi G4M2, code-named Betty, in surrender colours, white with green crosses.  (USAAF Photos)

Mitsubishi G4M Navy Type 1 Land-based Attack Aircraft, USAAF FE-2205, being prepared for flight testing.  (USAAF Photo)

Mitsubishi G4M2 Navy Type 1 Land-based Attack Aircraft, TAIC-SWPA, later USAAF FE-2205.  Some parts survive in the NASM.  (USAAF Photo)

There are no flyable or intact Mistubishi G4Ms left.  Several wrecks remain scattered in southeast Asia and on Pacific islands, although only one complete aircraft is known to be on display, a G4M1 Model 11, built in Nagoya Works No. 3 on 16 April 1942, tail number 370.  This aircraft, which had likely crash landed before mid-1944, was recovered from Babo Airfield, Indonesia, in 1991.  The wreck is on display in a diorama at the Planes of Fame Air Museum.  Several other locations display pieces of the G4M.

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