Mitsubishi G4M - Design and Development

Design and Development

The G4M was designed for a long range and high speed at the time of its introduction. Consequently, several weight-saving measures were incorporated into the design, such as dispensing with self-sealing fuel tanks, which caused Allied fighter pilots to give it derisive nicknames such as "the one-shot lighter", "the flying Zippo" and "the flying cigar" because of their tendency to explode or catch on fire from any slight damage to the fuel tank wings after being hit by aerial machine gun fire or ground antiaircraft fire. Similarly, pilots of the Imperial Japanese Navy despairingly called the G4M "Betty" the "Type One Lighter", "The Flying Lighter" or even the "Hamaki" ("Cigar"). This was partially due to the fact that on many occasions, the G4M was used for low-altitude torpedo attacks on shipping in which their performance advantages were negated, and the G4M was frequently shot down by antiaircraft artillery fire, and even by small arms. The "Betty"'s relatively large size made it an easy gunnery target, and the predictable approach path required for a torpedo run made for a generally easy interception by Allied fighter aircraft.

When used for medium to high-altitude bombing against stationary land targets like a supply depots, seaports, or airfields, "ease of interception" was another matter entirely. Using its long range and high speed, the G4M could appear from any direction, and then it could be gone before many fighters intercepted them. 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. Sometimes, assuming they did not catch fire in the first place after being hit in the wings by flak from the ground or machine gun bullets from enemy fighters, G4Ms also proved to be able to remain airborne despite being badly shot up. For example, after the attack of the 751 Kokutai attack on the USS Chicago during the Battle of Rennell Island, three out of four survivors (out of 11 aircraft committed to the attack) returned flying on only one engine.

Towards the end of World War II (1945), the "Betty" bomber was commonly used for carrying and launching kamikaze aircraft, and was the usual aircraft for carrying the Ohka kamikaze manned rocket-powered bombs.