Introduced into service in 1918 by the German Army during World War I, the MP 18 was intended for use by the Sturmtruppen, assault groups specialized in trench combat, as a short-range offensive weapon that would provide individual soldiers with increased firepower over a pistol.

Although MP 18 production ended after World War I, it was highly influential on subsequent small arms design; it formed the basis of most submachine guns manufactured between 1920 and 1960.

[3] What became known as the "submachine gun" had its genesis in the early 20th century and developed around the concepts of fire and movement and infiltration tactics, specifically for the task of clearing trenches of enemy soldiers, an environment within which engagements were unlikely to occur beyond a range of a few feet.

[4] The MP 18 is often credited as the very first submachine gun, as some sources discount the Villar Perosa, on account that it was originally fielded as a light support weapon on a mount.

[5] In October 1915 the Austro-Hungarian Standschützen-Battalionen trialed a submachine gun chambered in the 8x18mm Roth cartridge, known as the Maschinengewehr Hellriegel.

In late 1916, the Military Aviation Corps of the Italian Army created the first official demand for a submachine gun when they requested the development of a single-barreled Villar Perosa with a detachable stock, which was made in early 1917 and later adopted as the Carabinetta Automatica OVP, with 500 being issued to observation crews.

Contrary to popular belief, there is no concrete evidence that the Bergmann MP 18/I reached the front lines in early 1918 or that submachine guns were employed by German Sturmtruppen during the Spring Offensive.

The brigade received 216 MP 18/1 submachine guns for field trials in July 1918 – after the Spring Offensive ended.

Canadian troops from the 13th Battalion of the 5th Regiment Royal Highlanders of Canada were photographed with a captured MP 18/I on 11 August.

All MP 18s that were captured were low serial numbers, typically in the hundreds, a reasonable estimate is that around 4,000 guns saw combat.

A clause that appears in some copies reads "Automatic rifles and carbines are to be counted as light machine guns".

The government's implementation of the Treaty of Versailles in 1924 approved the distribution of maschinenpistole by the Ordnungspolizei (uniformed police, though probably meaning the SiPo), provided that they were not issued at a rate any higher than one gun for every twenty men.

[5] During the failed 1924 Estonian coup d'état attempt, the MP 18 was used to defend the Tallinn barracks from Communist militants; some of whom were armed with Thompson submachine guns.

It was merely a cheap and economical way for the German police to update their existing stocks of submachine guns to feed from the new Schmeisser box magazine without having to purchase entirely new orders of MP 28,IIs.

[5] Old stocks of MP 18/I submachine guns were distributed as foreign aid to allies of the Third Reich in neighboring countries.

[5] The MP 18 remained in limited service with the German armed forces during the Second World War, specifically with the Sicherheitsdienst, later eastern foreign divisions of the Waffen SS and also with Kriegsmarine coastal artillery units.

China produced many copies of the SIG Bergmann at various factories, including the arsenals at Tsing Tao, Dagu, and Hanyang.

The production was decentralized, and each factory's version exhibited differences from one another; the guns produced at Tsing Tao and Dagu had a bottom-mounted magazine.

The guns were sold under the name "Daniels Rapid-Fire Carbine" and were bought by members of the Northside Gang and the Chicago Outfit.

[2] Between 1927 and 1930 Estonia produced the Arsenal M23 submachine gun; a weapon based on the SIG Bergmann that used the 9mm Browning Long cartridge.

Some of these early guns were "sanitized", with no markings on the magazine housing except for a serial number, and occasionally they were fitted with a bayonet mount that screwed onto the ventilation holes of the barrel jacket.

Later, the marking "ANCIENS ETABLISSMENTS PIEPER S.A. HERSTAL" was added, in addition to proofing stamps by Woit Nicolas Cominoto.

[5] By 1933, with the Nazis gaining power and the Inter-Allied Commission of Control no longer enforcing the Versailles restrictions, Haenel was free to openly manufacture the MP Schmeisser.

It is easy to identify the Bergmann MP 32/34/35 or its final version 35/1 since the cocking lever works exactly like a rifle bolt.

In 1940, with a pressing need for individual automatic weapons, the British copied the MP 28 and developed the Lanchester submachine gun for the Royal Navy.

The British Sten used the side-mounted magazine configuration and a simplified version of the open-bolt firing operating system of the MP 28.

Soldiers liked to leave the bolt of their firearm in this closed or forward position, so dirt and debris would not enter the barrel and chamber.

This "bolt-closure" practice acted as a dust cover for the weapon's chamber, preventing a malfunction from occurring because of the presence of debris, but making accidental discharge more likely.

Later submachine gun designs like the Sten and the MP 40 were modified to allow the cocking handle to be pushed inwards to lock the closed bolt to the tubular receiver casing.

Its successor, the MP 28/2, received a modified mechanism with a selector for single shot or fully automatic fire.