The Mitsubishi G4M (Allied reporting name: Betty) was a Japanese twin-engined medium bomber used during World War II.
The first production model of the G4M series was the G4M1 Model 11. It was powered by two Mitsubishi Kasei 11 engines which gave it a top speed of 426 km/h. The G4M could carry up to 1,000 kilograms of bombs, one Type 91 torpedo, or an Ohka kamikaze aircraft. It was also armed with one Type 99 cannon and four Type 92 machine guns. Unfortunately, the aircraft had very little armor and no self-sealing fuel tanks, which made them easy to shoot down and earned them the nickname "flying cigarette lighter" from American pilots.[N 1]
The total length of the G4M1 was approximately twenty meters with a total weight of 6,800 kilograms unloaded. The operational range of the G4M meanwhile was excellent for the long range distances of the Pacific, at around 5,000 kilometers, with an additional 500 kilometers should the aircraft be flown as a transport without bombs loaded. Service ceiling of the aircraft maxed out at around 8,800 meters. To operate the aircraft, the G4M required a crew of seven men, thus casualties mounted quickly with the loss of so many aircraft due to poor armor.
The first variant of the G4M series was the G4M1 Model 11 which had the main distinction of featuring more powerful engines. However, this model as well as the original G4M1 Model 11 had undergone several improvements throughout their service lengths such as redesigned parts, added armor, etc., though none of the changes warranted the redesignation of the machine. Following came the G4M2 Model 22 which would feature a larger array of improvements. The G4M2 Model 22 for example hadimproved upon the base with addition of Kasei 21 engines with four propellers as well as the increase in size of the bomb bay. Its first subvariant meanwhile, the G4M2 ko sported a new 20mm Type 99 mounted in the dorsal gunner position for better defensive capabilities as well as a new radar system. The Otsu version simply had the upgraded Type 99 Mark 2 instead. The G4M2 Model 24 had once again, improved Kasei 24 engines with its ko and otsu subvariants being the same as those for the G4M2 Model 22. The main difference in subvariant though came with the hei model which introduced an additional Type 2 Machine Gun (13mm). Other subvariants of the G4M2 included those created to carry the Ohka flying bomb (G4M2 Model 24 tei).
The final variants of the series besides some transport modifications or trainer aircraft were the G4M3 Model 34, G4M3 Otsu, and G4M3 Hei. The G4M3 had introduced new Mitsubishi Kasei 25 engines and sported increased armor protection for crew and vital components. The however added further self-sealing fuel tanks, more armor plating, a redesigned tail turret, and had cut down the overall length of the aircraft by one meter.
These three examples only arrived by 1944 however so they did not reach the same combat potential they may have should they have arrived earlier such as in the 1942-1943 early island hopping campaign in the South Pacific. Still, the G4M3 and Model 34 were far more effective in combat than their predecessor, yet quickly fell prey to the also more advanced Allied fighters. Furthermore, only a mere 60 of these G4M3 types had been produced by the end of the war. One other variant of the series which did not carry on the bomber trend of the series was the G6M1, although only 30 had been built by the end of the war. This rare aircraft was a heavy fighter conversion, with 20mms and one 30mm autocannon replacing most if not all the 7.7mm machine guns on the aircraft.
Design work for the G4M was started in 1937 by Kiro Honjo and his design team, who had initially suggested a four engine aircraft to meet the J.N.A.F. requirement for a land bomber to replace the Mitsubishi G3M. This suggestion was rejected, and the G4M was completed as a twin engine aircraft in September 1939, making it's first flight on October 23, 1939. The "Betty" was entered service in 1941, with 2,446 being built until the war ended.
In the early conflicts that the aircraft had fought in, it served exceedingly well, it was very much a capable medium bomber for the time. However, its days of air superiority would not last as even as Allied aircraft technology advanced, the G4M design did not and the truly armored models of the G4M were simply not made nor introduced fast or early enough to keep the design in working order. Thus, the G4M became more ineffective the longer it remained in active service until the introduction of the G4M3, which even then, was still susceptible to Allied fire.
- The type's own crews referred to the G4M as the 'Type 1 Lighter'. The more tolerant dubbed the aircraft Hamaki (Flying Cigar).
- Green, William. Famous Bombers of the Second World War. Purnell Book Services. (1975), Page 118
- Lüdeke, Alexander. Weapons of World War II. Parragon Publishing (2007), Page 227
- Green, William. Famous Bombers of the Second World War. Purnell Book Services. (1975), Page 119