The Mitsubishi G4M or 一式陸攻 Ichishiki rikujō kōgeki ki, Isshikirikkō ("Type 1 land-based attack aircraft") was the main twin-engine, land-based bomber used by the Imperial Japanese Navy Air Service in World War II. The Allies gave the G4M the identification name of Betty.
The G4M was designed for long range and high-speed at the time of its introduction. Consequently, weight saving measures were incorporated into the design, such as dispensing withself sealing fuel tanks, which caused Allied fighter pilots to give it the derisive nicknames "one-shot lighter", "flying Zippo" and "flying cigar". Similarly, pilots of the Imperial Japanese Navy called the G4M the "Type One Lighter" and "Hamaki" ("Cigar"). This was due to the fact that on many occasions, it was used for low-altitude torpedo attacks where its performance advantages were negated. The "Betty"'s relatively-large size made it a large target to shoot at, and the simplified approach path on a torpedo run to attack a ship, meant for a generally easy interception.
When used for medium- to high-altitude bombing against stationary 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 be gone before many fighters could intercept them. The 20 mm cannon in the tail turret was much heavier armament than commonly installed in bombers, making dead astern attacks very dangerous. Sometimes, assuming they did not catch fire in the first place, G4Ms also proved to be able to remain airborne despite being badly shot up. For example, after 751 Kokutai's attack during the Battle of Rennell Island, three out of four survivors (of 11 aircraft that went to attack) returned flying on one engine only. Near the end of the war, the "Betty" was used as a common kamikaze-carrying and launching platform, and was the usual aircraft for carrying the Ohka kamikaze rocket aircraft.
The G4M was similar in performance and missions to other contemporary twin-engine bombers such as the German Junkers Ju 88 and Heinkel He 111, and the American B-25 Mitchell, and B-26 Marauder. These were all commonly used in the anti-shipping role. The G4M Model 11 was prominent in attacks on Allied shipping in the 1941 to early 1944 time-frame, but beyond that time, it was increasingly the easy prey of the ever-improving enemy fighters.
As torpedo bombers, the G4M's most notable use was in the sinking of Prince of Wales and Repulse off the coast of Malaya on 10 December 1941. They carried out the attacks alongside the older Japanese bombers, the Mitsubishi G3M "Nells" who were doing high-level bombing runs. The battleship Prince of Wales and battlecruiser Repulse were the first two capital ships ever to be sunk exclusively by air attack during a war, while at sea. Those bomber crews were a handful of selected Imperial Japanese Naval Air Force (IJNAF) aviators in prewar Japan, who had skills not only in torpedo-attacking at less than 9 m (30 ft) high but also in being able to navigate long-range flight over the ocean to spot a pinpoint target moving fast on the sea. The same squadrons in Kanoya Air Group (751 Ku), Genzan Air Group (753 Ku) and Mihoro Air Group (701 Ku), which sunk the British capital battle ships, later staged an extended series of attacks against American ships and land targets in Battle of Guadalcanal in the Solomon Islands, late 1942.