The 1902 “Grandpa” Nambu is one of the first wave of successful military automatic pistols, developed by Kijiro Nambu and his team over the course of 5 years, from 1897 to 1902. It was the first automatic pistol to be used by the Japanese military, although it was a private-purchase sidearm for officers and not formally purchased or issued by the military. It took several design cues from the C96 Mauser, in the form of a pivoting locking block and a bottlenecked cartridge.

The Grandpa was only made from 1902 until 1906, with less than 2400 examples produced in total - many of which were sold to Thailand. In 1906 a series of improvements were made to the gun, including increasing the size of the trigger and trigger guard, a swiveling lanyard ring, a slightly larger grip, new magazine, and deletion of the shoulder stock slot that had been standard on all previous Nambu pistols. The formal Japanese designation (Type A) did not change as a result, but in American collector parlance the new model became the “Papa” Nambu.