The first domestic design for a submachine gun appeared in Imperial Japan in around 1934, when the famous small arms designer Gen. Kijiro Nambu introduced a weapon of his own design. It was based on the already established Bergmann / Schmeisser pattern, but with one important change in design which was well ahead of its time. General Nambu decided to place a high-capacity curved box magazine inside the pistol grip of the weapon, making it noticeably shorter than contemporary rivals while maintaining similar barrel length. This gun, known as the Nambu Type I (some sources also designate is as Type II, first model or Type II A), was tested by the Imperial Japanese Army in 1936-37 but was rejected as unreliable. Apparently, small numbers of these submachine guns were manufactured by Nambu factory and used by Japanese Marine units in China in around 1937. During late 1930s Nambu also tried to offer his submachine gun for export sales, but without any success as the gun was chambered for the marginally powerful 8x22 pistol ammunition used only in Japan.
Nambu submachine gun was of simple blowback design, firing from open bolt. It was fitted with pneumatic rate-reducing buffer at the rear of the tubular receiver. Severely curved box magazine was inserted into the hollow pistol grip, which was necessarily canted forward, possibly resulting in awkward handling of the gun. Bottom of each magazine was fitted with small folding spade to be used as a support against the ground, when firing from prone position. Nambu submachine gun was fitted with fixed wooden shoulder stock and adjustable rear sight.