The Nambu Automatic Pistol Type B, or “Baby Nambu” as it is known in US collecting circles, is a scaled-down companion to the 1902 “Grandpa” Nambu pistol. It was intended as a private purchase option for officers who needed to carry a sidearm, but did not want or need a full size service pistol. It was chambered for the 7mm Nambu cartridge (roughly on par with .25ACP).
Despite its small size and light cartridge, the Baby Nambu copied the complete locking system of the larger Nambu, resulting in a quite expensive pistol. As a result, demand was slim, and only 6500 were manufactured between 1903 and 1929, when production ended. Most of these were made by the Tokyo Army Arsenal, although production did move to the TG&E company in about 1923 (presumably after the great Tokyo earthquake).