The submachine gun was developed during World War I (1914–1918). At its zenith during World War II (1939–1945), millions of SMGs were made. After the war, new SMG designs appeared frequently. However, by the 1980s, SMG usage decreased. Today, submachine guns have been largely replaced by assault rifles, which have a greater effective range and are capable of penetrating the helmets and body armor used by modern infantry. However, submachine guns are still used by military special forces and police SWAT teams for close quarters battle (CQB) because they are "a pistol-caliber weapon that's easy to control, and less likely to over-penetrate the target."
During World War I, the Austrians introduced the world's first machine pistol the Steyr Repetierpistole M1912/P16. The Germans also experimented with machine pistols by converting pistols such as the Mauser C96 and Luger P-08 from semiautomatic to fully automatic operation and adding detachable stocks. Carbine-type automatic weapons firing pistol rounds were developed during the latter stages of World War I by Italy, Germany and the United States. Their improved firepower and portability offered an advantage in trench warfare.
In 1915, the Italians introduced the Villar-Perosa aircraft machine gun. It fired pistol-caliber 9mm Glisenti ammunition, but was not a true submachine gun, as it was originally designed as a mounted weapon. This odd design was then modified into the Beretta OVP carbine-type submachine gun, which then evolved into the 9×19mm Parabellum Beretta Model 1918 after the end of World War I. Both the Beretta OVP and the Model 1918 had a traditional wooden stock, a 25-round top-fed box magazine, and had a cyclic rate of fire of 900 rounds per minute.
The Germans initially used heavier versions of the P08 pistol equipped with a detachable stock, larger-capacity snail-drum magazine and a longer barrel. By 1918, Bergmann Waffenfabrik had developed the 9 mm Parabellum MP 18, the first practical submachine gun. This weapon used the same 32-round snail-drum magazine as the Luger P-08. The MP 18 was used in significant numbers by German stormtroopers employing infiltration tactics, achieving some notable successes in the final year of the war. However, these were not enough to prevent Germany's collapse in November 1918. After World War I, the MP 18 would evolve into the MP28/II SMG, which incorporated a simple 32-round box magazine, a semi & full auto selector, and other minor improvements.
The .45 ACP Thompson submachine gun had been in development at approximately the same time as the Bergmann and the Beretta. However, the war ended before prototypes could be shipped to Europe. Although it had missed its chance to be the first purpose-designed submachine gun to enter service, it became the basis for later weapons and had the longest active service life of the three.
In the interwar period the "Tommy Gun" or "Chicago Typewriter" became notorious in the U.S. as a gangster's weapon; the image of pinstripe-suited James Cagney types wielding drum-magazine Thompsons caused some military planners to shun the weapon. However, the FBI and other U.S. police forces themselves showed no reluctance to use and prominently display these weapons. Eventually, the submachine gun was gradually accepted by many military organizations, especially as World War II loomed, with many countries developing their own designs.
The Italians were among the first to develop submachine guns during World War I. However, they were slow to produce them during World War II. The 9 mm Parabellum Beretta Model 1938 was not available in large numbers until 1943. The 38 was made in a successive series of improved and simplified models all sharing the same basic layout. The Beretta has two triggers, the front for semi-auto and rear for full-auto. Most models use standard wooden stocks, although some models were fitted with an MP 40-style under-folding stock and are commonly mistaken for the German SMG. The 38 series was extremely robust and proved very popular with both Axis forces and Allied troops (who used captured Berettas). It is considered the most successful and effective Italian small arm of World War II. The 38 series is the longest serving of the world's SMGs, as later models can still be seen in the hands of Italian military and police forces.