In order to maintain the speed and high-altitude performance of the G3M with a heavy payload, it lacked any form of defensive armour or self-sealing fuel tanks.

[1][2][3] The G3M has its origins in a specification submitted to the Mitsubishi company from the Imperial Japanese Navy requesting a bomber aircraft with a range unprecedented[citation needed] at the time.

The speed requirement submitted by the naval department was again also unprecedented[citation needed], not only in Japanese but also in international bomber aviation, where in relation to the envisaged Japanese battlegrounds of China and the Pacific, the bomber would need to not only cover long distances, but necessarily have exceptional speed to strike distant targets with a minimum attack time.

Thus the G3M was an embodiment of Japanese military aircraft design in the brief period leading to the Pacific War, with powerful offensive armament (in this case in the form of bombs and torpedoes) and range and speed emphasised over protection and defensive capabilities.

The lightweight structure and complete lack of defensive machine guns and the additional crew necessary to operate them (features in the early prototype design) were considered essential to maintain the speed and high-altitude performance of the G3M with a heavy payload.

The G3M flew for first time in 1935, taking off from a Nagasaki airfield belonging to Mitsubishi Heavy Industries and landing at Haneda Airport on the outskirts of Tokyo.

Wake Island was similarly bombed by G3Ms from the Chitose Kōkūtai on the first day of the war, with both civilian and US Navy infrastructure being heavily damaged on the ground.

Nells from the Genzan Kōkūtai provided important support during the attack on HMS Prince of Wales and Repulse (Force Z) near the Malayan coast.

From 1943 until the end of the war, the majority of G3Ms served as glider tugs, aircrew and paratroop trainers, and transports for high-ranking officers and VIPs between the home islands, occupied territories, and combat fronts.