The M.P.18,I (Maschinenpistole 1918) was a German submachine gun designed by Hugo Schmeisser and produced by Theodor Bergmann Abteilung Waffenbau Suhl from 1918 to 1920. Originally conceived as a portable machine gun for trench raids during World War I, the M.P.18,I influenced countless subsequent designs and is now widely considered to be one of the first practical submachine guns in history.
Hugo Schmeisser, then an employee of Theodor Bergmann's factory in Suhl, began working on the M.P.18,I in 1917. The project was initiated in response to a commission from the German Army, who requested a light, automatic, pistol-calibre weapon for trench combat. Bergmann's design was tested but no action was taken until early 1918, when it was finally accepted into service. Production at the Bergmann factory began immediately and the weapon was designated the M.P.18,I.
Issue of the M.P.18,I was reserved for Sturmtruppen; shock troopers who participated in assaults on enemy trenches. The first M.P.18,Is reached the German lines by the Summer of 1918 and only six were issued per company, despite initial plans to issue it to all COs and NCOs. It first saw action during the latter stages of the so-called "Kaiserschlacht" offensive of 1918, and saw little combat usage afterward. Despite this, it still managed to build up a positive reputation with German troops.
Contrary to popular belief, the contemporary reaction to the weapon from the Allied forces was largely apathetic. The British tested captured examples in September 1918 and found little to recommend in the weapon, believing the 9×19mm cartridge to be underpowered and that the weapon could be effectively countered by the use of body armor. An inquiry into whether British troops should be issued with a similar weapon was met with a negative response.
By the end of the war, about 35,000 M.P.18,Is had been produced in total. Restrictions imposed by the Treaty of Versailles led to the German Army drastically downsizing its arsenal of machine guns, and consequently most M.P.18,Is were taken out of service and issued to German police forces and Freikorps militias. The police issued one M.P.18,I per twenty officers. During the turbulent internal conflicts in post-war Germany, the M.P.18,I saw further combat use by the aforementioned factions.
The M.P.18,I was blocked from domestic production after World War I, due to the terms laid out in the Treaty of Versailles, which severely limited Germany's capacity to manufacture and export military armaments. Thus, production of the gun at the Bergmann factory ended in early 1919, and Theodore Bergmann sold the patent rights to SIG in Switzerland, who made modifications to the design, notably replacing the distinctive drum magazine with a straight box magazine. The Swiss version of the gun was known as the SIG M1920 and it was exported internationally, enjoying relative success.
The C.G. Haenel company of Suhl also converted standard M.P.18,I submachine guns to feed from straight box magazines during the interwar period. These guns were converted specifically for domestic German police use and were not exported. Although very similar to the SIG version, the Haenel M.P.18,I conversions retained the fixed rear sight rather than the adjustable tangent sight of the SIG M1920, and also featured a magazine release button on a diagonal section over the top of the magazine housing.
In 1923, Finnish-contract SIG M1920 submachine guns were studied in Estonia, who produced a copy at a state arsenal in Tallinn. This gun, the Tallinn Model 1923, was not made in great numbers. Another copy of the SIG M1920 was produced in China during the Chinese Civil War, and was known as the Tsing Tao after its place of manufacture. This version used a vertically-loading magazine.
Ten years after the introduction of the original M.P.18,I, Hugo Schmeisser himself designed an improved model known as the M.P.28,II, which was also based on the SIG version. The M.P.28,II was initially produced in Belgium to work around the restrictions on Germany's arms industry, but when the Nazis came to power in 1933, the Treaty of Versailles was ignored and production of the gun was allowed to take place domestically at the C.G. Haenel plant in Suhl. The M.P.28,II was widely exported before World War II and was in limited issue with German troops during the war.
The M.P.18,I was a basic blowback-operated submachine gun that fired from an open bolt, housed inside a tubular receiver fitted to a short wooden stock. The bolt rode on a guide rod enveloped by the return spring. It had no fire selector and could fire in full-automatic only. The magazine was a 32-round "snail" magazine, also known in German as a Trommelmagazin, which consisted of a straight stick with a small spring-loaded round drum fixed to the end. This magazine fed into the left side of the receiver, whilst the cocking handle was located on the right side. The M.P.18,I could also accept 8-round Luger magazines, although these were rarely issued with the gun.
The design pattern of the M.P.18,I served as the basis for many subsequent submachine guns that appeared after World War I, as the relative simplicity of the gun ensured that it functioned reliably. The only aspect of the M.P.18,I that proved unsuccessful was the magazine design, which was made obsolete by the development of more basic box magazines.