Nambu pistol

 were a series of semi-automatic pistols produced by the Japanese company Koishikawa Arsenal, later known as the Tokyo Artillery Arsenal. The series had five variants, the Type A Model 1902 (also called the Grandpa Nambu), the Type A Model 1902 Modified (also known as the Papa Nambu), the Type B (also known as the Baby Nambu), the Type 14 (南部十四年式自動拳銃) and the Type 94. The Nambu pistols were designed to replace Japan's earlier service pistol, the Type 26 Revolver.
The pistols were designed by Kijiro Nambu and saw extensive service in the Empire of Japan during the Second Sino-Japanese War and Pacific War. The most common variant, the Type 14, was used mostly by officers, who had to pay for their pistols themselves. 
Towards the end of the war, the production quality began to decline in order to speed up manufacture. Nambu pistols were noted for their lack of reliability and stopping power compared to other handguns being fielded by other nations at the same time, such as the M1911 and Walther P38.
History.
Prior to the design of the Nambu, the only pistol in Japanese service was the Type 26 Revolver, which served with distinction during the First Sino-Japanese War (1894-1895). However, in the 1890s, semi-automatic pistol designs began to emerge, among them, the Mauser C96, which was influential in the production of the Nambu, as it uses the same locking mechanism as the C96, and the Nambu was designed shortly after a Japanese commission reported on European military developments.
The first Nambu, the Type A, was completed in 1902. This version was never adopted, but some were sold to China and Siam. The Type B was adopted by the Imperial Japanese Navy and Royal Thai Army during the 1920s, and the later Type 14 was adopted in 1926 (Taishō 14) as the service pistol of the Imperial Japanese Army until its surrender in 1945. Nambu pistols were symbols of prestige, often carried in fanciful holsters, and were used more as a means of ornament and status rather than actual combative purposes. Japan produced about 400,000 Nambu pistols over the course of the war, whereas in this same time period the United States had made over a million M1911 pistols. 
Alongside other Japanese weapons, such as guntōs and Arisaka rifles, many American servicemen took Nambu pistols home with them as war trophies. Production of Nambu pistols ceased after the end of the war, when the Japan Self-Defense Forces replaced it with the SIG Sauer P220.
Design.
The Nambu pistol is a recoil operated, locked breech, semi-automatic pistol. The Type A and 14 Nambus have a magazine capacity of 8 rounds, whereas the Type B had 7. A common flaw in the series was that the gun's safety catch and its magazine release did not enable the magazine to slide out of the gun once it was completely empty, forcing the operator to work against the weight of the recoil spring and leaf spring, making reloading needlessly difficult. In response to this issue, the magazine catch was removed from the Type 14. Another issue with the safety was that it was located just above the trigger guard, meaning that it could not be activated with the same hand that was holding the pistol.
The grip on the Nambu is slanted, which made feeding the magazine a needlessly delicate procedure. The magazine spring is only about 60% effective, and the bullets moving against the walls of the magazine causes frictional loss, weakening the spring further. Furthermore, the size of the bullets had to be exact; soft point and cast lead bullets would fail to chamber properly.
The Nambu pistol uses the 8×22mm Nambu cartridge, which made it substantially weaker than other handguns. The 8mm round's muzzle energy was less than half that of the 9×19mm Parabellum (used in the Walther P38), and the 7.62×25mm Tokarev (used in the TT-33). 
Type A.
The first type of Nambu that was produced was the Type A. Type A Nambus produced from 1903-1906 had differences from those produced after 1906, and, among collectors, the original Nambus are commonly referred to as Grandpa Nambus. The 'Grandpa' Type A was produced until around serial number 2400. Production of the Type A Nambu ceased as of 1923, as the Type 14 was both cheaper, and more effective. The Nambu Type A somewhat resembles the Luger pistol in appearance, but this is superficial.
A later version of the Type A Nambu, the Type A Modified, also known as the Papa Nambu, was produced until around serial number 7000. The trigger guard of the 'Grandpa' Nambu was enlarged in later models. The Type A originally had a provision that allowed for the installation of a stock, as seen on the Mauser C96. However, there are no known instances of a Nambu pistol being fitted with a stock.
Type B.
Due to failings with the Type A Nambu, an improvement, the Type B, was devised. Both the pistol itself, and the round it fired, was smaller than the other Nambu pistols, leading to the name 'Baby Nambu'. Type B Nambus were produced at the Tokyo Artillery Arsenal. The first 450 models had the bottom part of the magazine made of wood, and only one diameter firing pin, but later Type Bs made the magazine aluminium, and incorporated a multiple diameter firing pin. The Type B Nambu was never adopted officially by any Japanese armed forces. As was customary in the Imperial Japanese Army, officers paid for pistols with their own salaries, but the Type B Nambu was unable to achieve market success as they were twice the price of comparable imported pistols, such as the FN M1900. A Type B Nambu sold for 180 yen, making it cost roughly the same as a Captain's entire monthly salary.
After the 1923 Great Kantō earthquake, Koishikawa arsenal stopped producing new parts for Type B Nambus, but continued to assemble ones with pre-existing parts until 1929.
Type 14.
The Type 14 Nambu, which gets its namesake from the year it was produced - the 14th year of the Taishō era, or 1926. It was designed to help lower the manufacturing cost of the Nambus, and like the Type A, fired the 8×22mm Nambu. From 1927, it was a standard issue sidearm for officers. It is believed that around 400,000 Type 14 Nambus were produced, but the exact number is unknown, as Japanese soldiers considered their weapons property of the emperor, and many chose to destroy their pistols or throw them into the ocean, to avoid them falling into enemy hands. 
Later production models have a larger trigger guard, following complaints by soldiers stationed in Manchukuo that it was difficult to fire the trigger while wearing gloves. Some of these models also have a knurled steel cocking knob instead of the standard "slotted" cocking knob. After 1940, an auxiliary magazine spring was added to assist in reloading. A redesigned cocking knob was implemented in 1944 in order to simplify production. The Type 14 also lacks the grip safety used on the previous models.
Pre-1937 Type 14s are well made, with a noticeable decline in quality to meet the production demands of wartime. However, later Type 14s remained mostly functional despite the decreased quality. The holsters for the pistols also had to be changed to accommodate wartime. A lack of available raw materials resulted in a move from holsters made of leather, to rubberized canvas.
Legacy.
In 1949, William B. Ruger took design elements of the Nambu in his own design, which would become the Ruger Standard. This was the first weapon designed by Sturm, Ruger & Co. The Ruger Standard would become the most successful .22LR pistol ever produced, and as of 2016, Ruger's company produced more firearms than any other American company, and was worth over $600 million.
Because of their rarity and historical significance, Nambu pistols would become sought after by gun collectors, with models selling anywhere from $800 to $1,500.