Despite being an extremely fragile aircraft, the Mitsubishi G4M 'Betty' became the most widely used and produced Japanese naval bomber of the war. As a tradeoff to its impressive range and bomb load, the G4M lacked all sorts of standard protective measures for the crew and the fuel tanks which were commonplace in other contemporary designs. In fact, large areas of the wings were used (un-protected) for fuel storage and US fighter pilots soon discovered that it took little to bring down a G4M something which resulted in the unflattering nickname of "Flying Lighter". 'Bettys' were used successfully in the attacks on the HMS Prince Of Wales and HMS Repulse in 1941 and also were the aircraft that were carrying Admiral Yamamoto and his staff when they were intercepted and shot down by P-38s on 18 April 1943. Throughout the rest of the war, G4Ms saw widespread service including as carriers for Japan's suicide missile (the MXY-7 Okha) and were used to ferry the Japanese surrender delegation to Io Shima on 19 August 1945, their final memorable wartime action.

The G4M prototype first flew on 23 October 1939 and eventually entered service as the G4M1 which saw action against China and the Allies during the opening stages of the war. Improvements in armament, engine and fuel capacity as well as redesigned features led to the G4M2, the main variant from 1943 onwards which was constantly upgraded as the need arose. Finally, the G4M3 introduced better crew protection but was built in modest numbers. Interestingly, a heavy escort fighter known as the G6M1 was developed from the prototype and preceded the initial G4M production units, however, most of these were eventually converted to trainers (G6M1-K) or paratroop transports (G6M-L2).