Mitsubishi G4M


The G4M- Allied reporting-name "Betty" - was the main heavy bomber of the Japanese Navy during World War II. It was remarkable for its long range, but this was achieved by depriving the aircraft of armour while providing it with huge fuel tanks in the wings. Since the tanks were not self-sealing the Betty was extremely vulnerable, tending to go up in flames whenever hit. This led to its receiving the derisive nicknames "the One-Shot Lighter" and " the Flying Cigar." Despite its range and speed, it was therefore - not surprisingly - unpopular with its crews.

The G4M's single outstanding success was achieved at the start of the Pacific War when, on 10 December 1941, only three days after Pearl Harbor, G3M Nell's and G4Ms of the 22nd Air Flotilla sank two British capital ships - the new battleship Prince of Wales and the old battlecruiser Repulse off the coast of Malaya. This action - sometimes known as "The Battle of the Gulf of Siam" - is more often referred to as "The Destruction of Force Z."


The first attacks on Allied forces to be made following the Guadalcanal landings were carried out by G4Ms flying from Rabaul. An attack on the US transports by 26 Betties was to demonstrate to Allies and Japanese alike the vulnerability of the G4M to anti-aircraft fire. At least 17 Betties were shot down. One aircraft damaged by gunfire made a suicide crash on the transport George F. Elliott. The resulting fire destroyed the ship - this was the only damage inflicted by Japanese air attacks in reaction to the Allied landings.


G4Ms operated throughout the six months of fighting on Guadalcanal, suffering heavy losses. By early 1943 the Japanese Navy had developed new techniques for night torpedo attack. These were put into effect on the night of 29/30 January 1943 in the Battle of Rennell Island, in which Betties torpedoed and sank the heavy cruiser Chicago. G4Ms repeatedly harassed US task groups in night attacks from this time until almost the end of the war, occasionally inflicting heavy damage - for example in February 1944 when a Betty torpedoed the Essex Class carrier Intrepid after Task Force 58's raid on the Japanese base of Truk in the Caroline Islands.


The G4M had been designed to meet a very demanding Navy specification of 1938. Mitsubishi repeatedly advised the Navy that a four-engined design would be preferable, but the Navy insisted on the restriction to two engines. The G4M1 flew its first missions in China in May 1941. Engine-power and fuel capacity were increased with the G4M2, the version produced in the greatest numbers. In the G4M3 the balance of the design was dramatically changed, with full protection being provided and fuel capacity being drastically reduced.


In 1945 specially-modified G4Ms were employed to carry the Ohka rocket-propelled piloted bomb. This development was in general a disastrous failure, since the modified G4Ms when carrying the Okha were hopelessly vulnerable to fighter attack - although if the G4M succeeded in launching the Okha within range of allied ships the weapon then often proved devastating.


Total production of the G4M was 2,479 - a remarkably high figure for a Japanese medium or heavy bomber.




Type: Land-based naval torpedo-aircraft and bomber.

Dimensions: Span 81' 8"; length 65' 6"; height 16' 1"



(G4M1) 14,860 lb empty, 20,944 lb loaded

(G4M2) 17,623 lb empty, 27, 550 lb loaded

(G4M3) 18,500 lb empty, 27,550 lb loaded



(G4M1) Two 1,530 hp Mitsubishi Kasei-11 14-cylinder two-row radials

(Subsequent versions) Two Kasei-22 rated at 1,850 hp with water/methanol injection


Performance -

(G4M1) Maximum speed 265 mph; initial climb 1,800 feet per minute; service ceiling approx 30,000 feet.

(G4M2) Maximum speed 271 mph; initial climb 1,380 feet per minute; service ceiling approx 30,000 feet.

(G4M3) Maximum speed 283 mph; initial climb 1,380 feet per minute; service ceiling approx 30,000 feet.


Range: (G4M1) 3,130 miles (G4M2) 2,980 miles (G4M3) 2,262 miles.


Armament (typical) -

3 x 7.7 mm manually-aimed machine guns in nose, dorsal and ventral positions

1 x 20 mm manually-aimed cannon in tail.

Internal bomb load of 2,205 lb, or one 17.7-inch torpedo



Source for the above data was Bill Gunston's "Combat Aircraft of World War II" The profile drawing of the G4M is reproduced with thanks from "Jane's War at Sea 1897 - 1997 Centennial Edition"

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