MItsubishi G4M, part one

 

The G4M was designed as a long range and high speed bomber at the time it was introduced. In order to meet the ambitious specifications issued by the Imperial Japanese Navy (IJN) which called for a bomber capable of achieving a top speed of 398 km per hour (247.306 mph), a service ceiling of 3.000 m (9.800 ft), a range of 4.722 km (2.934 milles) unloaded and 3.700 km (2.300 milles) when loaded with 800 kg (1.800 lb) of payload, Mitsubishi's team, lead by Kiro Honjo, did not incorporate self-sealing fuel tanks and armour plating in order to save weight to achieve a longer range. This decision made both the A6M Zero and the G4M vulnerable to machine gun and anti-air fire. 

Japanese pilots nicknamed the G4M as "Hamaki" (cigar) because of its shape and Allied pilots nicknamed it as "the flying lighter", "the flying zippo" or "the one-shot lighter" because of its easiness to ignite when hit in the wing fuel tanks. 

Given some defensive deficiencies observed on the previous model, the G3M, the first production variant, the G4M1 included a single 7.7 mm (0.303 in) Type 92 machine gun in the nose. This first variant carried also a dorsal Type 92 machine plus two additional ones located in lateral beams. The tail was guarded by a single 20 mm Type 99 cannon placed inside a cupola. The whole machine was powered by two Mitsubishi Mk4A Kasei 11 radial engines which delivered 1.530 hp of power and had a payload of up to 1.000 kg (2.204 pounds) of bombs or a single 858 kg (1891.57 pounds) aerial torpedo.

In retrospective, the G4M was, in terms of performance, similar to other contemporary medium bombers such as the German Heinkel He.111, the North American B-25 Mitchell or the Vickers Wellington. Just like these bombers, the G4M was extensively in anti-shipping strikes from 1941 until 1944 when it became a rather easy prey for Allied fighters.

It was used for the first time in combat on 13th September 1940 in mainland China, in a bombing raid against the city of Hankow. Twenty-seven G4M of the 1st Rengo Kokutai departed from Taipei, Omura and Jeju escorted by 12 A6M Zero fighters. Similar bombing operations took place in May 1941. In December 1941 one hundred and seven G4Ms departed from Taipei, Formosa, crossed the Luzon strait and bombed the Philippines, opening the Japanese invasions in the South-Western Pacific Theatre. 

During the first year of combat, the G4M was a success. They bombed Clark Field, the main US Army Air Base in the Philippines on 8th December 1941 and was instrumental at the aerial raid that sank both HMS Prince of Wales (53) and HMS Repulse (34) Battleship and Battlecruiser respectively. Two days later, they took part in the bombing of Katherine, in Australia, being that the deepest inland attack on Australian territory during the whole war at over 200 milles (322 km). The G4M took advantage of the Allied weak fighter opposition during the earliest stages of the War in the Pacific, and attacked targets ranging from the Aleutian Islands to Australia, thanks to its long range. The flaw of not having self-sealing fuel tanks wasn't an inconvenience at this early point of the theatre.

Sources:

1. https://en.wikipedia.org/wiki/Mitsubishi_G4M

2. https://www.valka.cz/topic/view/1284

3. Bunrin Do - Famous Airplanes Of The World 59 - Mitsubishi G4M Betty (translated as much as we could)