I think that this is one of the better Explanations. Grumpy
Submachine gun- Wiki
A submachine gun (SMG) is a magazine-fed, fully automatic carbine designed to fire pistol cartridges. The term “submachine gun” was coined by John T. Thompson, the inventor of the Thompson submachine gun.
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.”
History in the 20th Century
World War I
In the early 20th century, experimental machine pistols were made by converting pistols such as the Luger P-08 and Mauser C96 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.
By 1918, Bergmann Waffenfabrik had developed the MP 18, the first practical submachine gun. This weapon fired the 9×19mm Parabellum round and used the same 32-round snail-drum magazine as the Luger P-08. The MP 18 was used in significant numbers by
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 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 Thompson’s 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.
World War II
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 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.
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.
However, the MP38 production was still just starting and only a few thousand were in service at the time. It proved to be far more practical and effective in close quarters combat than the standard-issue German Kar 98K bolt-action rifle.
The MP40 was lighter than the MP38. It also used more stamped parts, making it faster and cheaper to produce.
During the Winter War, the badly outnumbered Finnish used the Suomi KP/-31 in large numbers against the Russians with devastating effect. Finnish ski troops became known for appearing out of the woods on one side of a road, raking Soviet columns with SMG fire and disappearing back into the woods on the other side.
During the Continuation War, the Finnish Sissi patrols would often equip every soldier with KP/-31s. The Suomi fired 9 mm Parabellum ammo from a 71-round drum magazine (although often loaded with 74 rounds).
The PPSh’s 71-round drum magazine is a copy of the Suomi’s. Later in the war they developed the even more readily mass-produced PPS submachine gun.
The USSR would go on to make over 6 million PPSh-41s and 2 million PPSs by the end of World War II. Thus, the Soviet Union could field huge numbers of submachine guns against the Wehrmacht, with whole infantry battalions being armed with little else.
Even in the hands of conscripted soldiers with minimal training, the volume of fire produced by massed submachine guns could be overwhelming.
In 1941, Britain adopted the 9 mm Parabellum Lanchester submachine gun. Following the Dunkirk evacuation, and with no time for the usual research and development for a new weapon, it was decided to make a direct copy of the German MP 28.
However this gun, the Lanchester, proved to be difficult and expensive to manufacture. Shortly thereafter, the much simpler, cheaper and faster to make STEN submachine gun was developed.
Over 4 million STEN Guns were made during World War II. The STEN gun was so cheap and easy to make that Germany started manufacturing their own copy (the MP 3008) towards the end of World War II.
After the war, the British replaced the STEN with the Sterling submachine gun. Britain also used many M1928 Thompson submachine guns during World War II.
The United States and its allies used the Thompson submachine gun, especially the simplified M1. However, the Thompson was still expensive and slow to produce. Therefore, the U.S. developed the M3 submachine gun or “Grease Gun” in 1942, followed by the improved M3A1 in 1944.
While the M3 was no more effective than the Tommy Gun, it was made primarily of stamped parts and welded together, and so, it could be produced much faster and at fraction of the cost of a Thompson.
It could be configured to fire either .45 ACP or 9mm Luger ammunition. The M3A1 was among the longest serving submachine guns designs, being produced into the 1960s and serving in US forces into the 1980s.
After World War II
After World War II, “new submachine gun designs appeared almost every week to replace the admittedly rough and ready designs which had appeared during the war.
Some (the better ones) survived, most rarely got past the glossy brochure stage.” Most of these survivors were cheaper, easier and faster to make than their predecessors. As such, they were widely distributed.
In 1945, Sweden introduced the 9mm Parabellum Carl Gustav M/45 with a design borrowing from and improving on many design elements of earlier submachine-gun designs.
It has a tubular stamped steel receiver with a side folding stock. The M/45 was widely exported, and especially popular with CIA operatives and U.S. Special Forces during the Vietnam War.
In U.S. service it was known as the “Swedish-K”. In 1966, the Swedish government blocked the sale of firearms to the United States because it opposed the Vietnam War.
In 1946, Denmark introduced the Madsen M-46, and in 1950, an improved model the Madsen M-50. These 9mm Parabellum stamped steel SMGs featured a unique clamshell type design, a side folding stock and a grip-safety on the magazine housing.
The Madsen was widely exported and especially popular in Latin America, with variants made by several countries.
In 1948, Czechoslovakia introduced the Sa vz. 23 series. This 9mm Parabellum SMG introduced several innovations: a progressive trigger for selecting between semi-automatic and full auto fire, a telescoping bolt that extends forward wrapping around the barrel and a vertical handgrip housing the magazine and trigger mechanism.
In 1949, France introduced the MAT-49 to replace the hodgepodge of French, American, British, German and Italian SMGs in French service after World War II.
The 9mm Parabellum MAT-49 is an inexpensive stamped steel SMG with a telescoping wire stock, a pronounced folding magazine housing and a grip safety.
This “wildebeest like design” proved to be an extremely reliable and effective SMG, and was used by the French well into the 1980s. It was also widely exported to Africa, Asia and the Middle East.
The Uzi was one of the first weapons to use a telescoping bolt design with the magazine housed in the pistol grip for a shorter weapon.
It is a small, compact, very well made SMG and among the first to use telescoping bolt design. The M12 was designed for mass production and was made largely of stamped steel and welded together.
It is identified by its tubular shape receiver, double pistol grips, a side folding stock and the magazine housed in front of the trigger guard. The M12 uses the same magazines as the Model 38 series.
This makes the MP5 more accurate than open-bolt SMGs, such as the UZI. The MP5 is also one of the most widely used submachine guns in the world, having been adopted by 40 nations and numerous military, law enforcement, intelligence, and security organizations.
While these SMGs received enormous publicity, and were prominently displayed in films and television, they were not widely adopted by military or police forces.
By the 1980s, the demand for new submachine guns was very low and could be easily met by existing makers with existing designs.
However, several manufacturers began designing Submachine guns based on their existing assault rifle patterns. These new SMGs offered a high degree of parts commonality with parent weapons, thereby easing logistical concerns.
The magazine well is modified using a special adapter to allow the use of smaller 9mm magazines. The magazines themselves are a copy of the Israeli UZI SMG magazine, modified to fit the Colt and lock the bolt back after the last shot. The Colt is widely used by U.S. police forces and the USMC.
In 1998, H&K introduced the last widely distributed SMG, the UMP “Universal Machine Pistol”. The UMP is a 9mm, .40 S&W, or .45 ACP, closed-bolt blowback-operated SMG, based on the H&K G36 assault rifle.
It features a predominantly polymer construction and was designed to be a lighter and cheaper alternative to the MP5. The UMP has a side-folding stock and is available with four different trigger group configurations. It was also designed to use a wide range of Picatinny rail mounted accessories 
In the 2010s, assault rifles have replaced submachine guns in most roles. Factors such as the increasing use of body armor and logistical concerns have combined to limit the appeal of submachine guns.
However, SMGs are still used by police (especially SWAT teams) for dealing with heavily armed suspects and military special forces units for close quarters combat, due to their reduced size, recoil and muzzle blast.
Submachine guns also lend themselves to the use of suppressors, particularly when loaded with subsonic ammunition. Variants of the Sterling and Heckler & Koch MP5 have been manufactured with integral suppressors.
Personal defense weapons
Developed during the late 1980s, the personal defense weapon (PDW) is touted as a further evolution of the submachine gun.
The PDW was created in response to a NATO request for a replacement for 9×19mm Parabellum submachine guns. The PDW is a compact automatic weapon that can defeat enemy body armor and which can be used conveniently by non-combatant and support troops, and as a close quarters battle weapon for special forces and counter-terrorist groups.
Introduced in 1991, the FN P90 features a bullpup design with a futuristic appearance. It has a 50-round magazine housed horizontally above the barrel, an integrated reflex sight and fully ambidextrous controls.
A simple blowback automatic weapon, it was designed to fire the FN 5.7×28mm cartridge which can penetrate soft body armor. The P90 was designed to have a length no greater than a man’s shoulder width, to allow it to be easily carried and maneuvered in tight spaces, such as the inside of an armored vehicle.
Introduced in 2001, the Heckler & Koch MP7 is a direct rival to the FN P90. It is a more conventional-looking design. The MP7 uses a short-stroke piston gas system as used on H&K’s G36 and HK416 assault rifles, in place of a blowback system traditionally seen on submachine guns.
The MP7 uses 20-, 30- and 40-round magazines and fires 4.6×30mm ammunition which can penetrate soft body armor. Due to the heavy use of polymers in its construction, the MP7 is much lighter than older SMG designs, being only 1.2 kg (2.65 lb) with 20-round empty magazine.
Other sources refer to SMGs as “machine pistols” because they fire pistol-caliber ammunition, for example, the MP-40 and MP5, where “MP” stands for Maschinenpistole (“Submachine gun” in German, but cognate with the English term “Machine pistol”).
Firearms like the FN P90 and H&K MP7 are also referred to as Personal Defense Weapons because the small-caliber, high-velocity ammunition is claimed to offer superior performance to conventional pistol ammunition.
- Assault rifle
- Firearm action
- List of submachine guns
- Machine gun
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- Overview of gun laws by nation
- Personal defense weapon
- Semi-automatic pistol
- Sputter Gun
- Submachine gun competition
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