The Imperial Japanese Navy purchased a Douglas DC-4E through Nippon Koku K.K. (Japan Air Lines), after had been rejected by airlines in the United States. Once it arrived in Japan in 1939 it was given to Nakajima to dismantle and study to develop the Experimental 13-Shi Attack Bomber Shinzan (mountain recess).
It was found that the G5N didn't perform very well which was most likely caused by the inexperience of the designer which lead to an overweight aircraft.
The G5N1 had four engines, which was a first for the Imperial Japanese Navy.
A first for Japanese aircraft the G5N1 had tricycle landing gear.