The Japanese used two kinds of imported Sub Machine Guns which were called as "Bergmann Sub Machine Gun" in Japan. One is the SIG M1920 imported from Switzerland and another is the MP34/I imported from Germany. SIG M1920 is the licenced copy of MP18/I.
Bergmann Sub Machine Gun was mainly used by SNLF in the Chinese-Japanese War. Especially, the SNLF soldiers equippied with a Bergmann SMG were very effective in the battle of the Shanghai Incident. This success made the IJA develop a Japanese SMG.
Type 100 SMG was developed by IJA, based on Bergmann Sub Machine Gun. It is an air cooled, blowback operationed, full-automatic machine pistol. It used 8mm Numbu bullet, common to Numbu pistols. A bayonet can be attached at the barrel. The right photo shows a airborne model of Type 100. It can be folded at the bottom of the stock.
Type 100 was deployed into paratroops. Paratroopers in Palembang, Leyte and Okinawa were equipped with Type 100.
An improved model of Type 100 was developed in 1944. The improved model was simplified and its rate of fire was increased to 800 rounds. The left photo shows an improved model. It is said that 7,000 to 8,000 of the improved model Type 100 were produced, but they were reserved for the battle of Japan proper.