This, the first production version, was powered by two 910 hp Mitsubishi Kinsei 3 radial engines, and had a defensive armament of three 7.7 mm (0.30 caliber) machine-guns, in two dorsal and one ventral turrets, all turrets being retractable. Only 34 of this version were produced before 1,075 hp Kinsei radials became available. These resulted in the G3M2 Model 21, which as well as the more powerful engines had increased fuel capacity.
The new aircraft soon demonstrated their capabilities on 14 August 1937 when a force of G3M2s based on Taipei in Formosa attacked targets in China 1,250 miles away - the first transoceanic air attack in history.
The Model 21 was succeeded by the G3M2 Model 22 in which the defensive armament was increased to one 20mm cannon and four 7.7 mm machine-guns. The crew was increased from five to seven, including two additional gunners to man the enhanced armament. The Model 23 featured Kinsei 51 engines and further increased fuel capacity.
In all 1,048 G3Ms were built (636 by Mitsubishi and 412 by Nakajima), many of which were converted for use as transports. In the Pacific War the allies designated the bomber versions 'Nells' and the transports 'Tinas'.
The G3M remained in service throughout the war , although by 1943 the majority were being employed in second-line duties. It was succeeded by the Mitsubishi G4M - allied codename 'Betty'. Mitsubishi G3Mss and G4Ms achieved their most spectacular operational success on 10 December 1941, when off the coast of Malaya they sank - with torpedoes - the British battleship 'Prince of Wales' and battlecruiser 'Repulse'.