[3] A small number of the earlier version were converted into using folding stock, sometimes referred to by the Allies as the Type 100 navy, which was made for parachutists.

Although around 6,000 models of the SIG Bergmann 1920 (a licensed version of the German MP 18) and a few Solothurn S1-100s were purchased from Switzerland and Austria in the 1920s and 1930s, and were used in the invasion of China in 1937,[1] mass production of a native submachine gun did not begin until 1944.

The new simpler design was based on the imported European "Bergmann type" submachine guns, which had been used effectively in both Battles of Shanghai by Japanese marines.

A portion of the weapons for cavalry units were mounted with a bipod and a sight up to 1,500 meters to assess it capabilities in comparison with the bulky Type 11 light machine gun.

However, no major order was made for the new weapon as the interest of the army had turned to the new 7.7 mm Type 99 light machine gun.

Under a low-priority military contract the Type 100 began to be deployed in August 1942, with numbers not exceeding 1,000 units, of which around 200 were converted to folding stock models for use by army paratroopers.

[8] In connection with the lower quality "substitute standard" variants of other Japanese weapons to increase speed and reduce cost of manufacture, a number of changes were made to simplify the Type 100.

The 1944 variant was slightly longer, with simple iron sights and a greatly simplified muzzle brake consisting of two ports drilled in the barrel.