The sub-machine gun (SMG) is a pistol calibre, fully automatic weapon used for close quarter combat. It has several names:

• USA - sub-machine gun
• UK - machine carbine (later - sub-machine gun)
• Germany - Maschinenpistole (machine pistol)
• Russia - pistolet pulemyot (pistol machine gun)
• France - mitraillette (mini machine gun)
• Italy - moschetto auto (machine carbine)

The calibre is commonly 9mm Parabellum or similar. The effective range is 30m and rates of fire range from single shot to 1000rpm (rounds per minute) although the effective rate of fire is about 120rpm due to magazine changes and hot barrels. The standard method of operation is blowback or spent case projection, which uses Newton's Third Law of Motion - for every action, there is an equal and opposite reaction.

Operation

A heavy block is forced forwards by spring pressure, strips a round from the magazine, loads it into the breech then fires it. The charge expands in all directions but cannot expand sideways due to the case and the breech wall. The bullet takes the forward pressure and the base of the case the rearward. The block effectively stops the case moving backwards by weight and forward motion.

The bullet is the lighter load and moves off down the barrel. By the time it leaves the barrel, enough momentum will have built up to force the case and block backwards. This extracts and ejects the case and continues until the spring is compressed and halts the motion to the rear. If nothing stops the block, the cycle starts again. This is only safe and effective with a pistol round.

Most SMGs that use this method are inherently dangerous. The short length makes them easy to turn and point, possibly including friendly troops as well as the enemy. A gun could fire when dropped or through poor manufacture. Most users were well aware of this - as was anyone nearby!

Beginnings

The idea of a light automatic firearm was developed towards the end of the First World War and the weapon was first used by the German Army in the Spring Offensive of 1918. This was the MP 18 I which used the Lüger pistol 'snail' magazine. The first sub-machine guns were over-engineered and heavy, but stable, firing platforms. A classic example was the Thompson SMG of 1928 - wooden stocked and machined from solid steel stock weighing in at 12-16lb (6-8kg) depending on the magazine capacity. Its 45-calibre round (.45 ACP) was hard to control but very effective.

Arming Millions

The sub-machine gun's finest hour was the Second World War. The low pressures and forces involved in firing a pistol round meant that it could be made lighter by using thinner metal, without the supportive stock of a rifle. Usually only the barrel and block were made of machined metal, the rest being pressed steel sheet, tube and poor quality wood or plastic. This was cheap and easy to produce at a time when quantity outweighed quality and although the range was poor, the rapidity of fire won the day at close range. At first, such guns resembled rifles but later versions had folding stocks and pistol grips, the most famous being the German MP38 and MP40 (aka Schmeisser).

Most of these were cheap-and-nasty weapons of war. The British Sten gun based on the German 9mm Parabellum round, was made of 47 parts, mainly cheap tubing and steel sheet with an 8 inch (20cm) barrel and weighed 7lb (3.5kg) in fighting trim. It was vaguely rifle-stocked (no pistol grip) but later versions had wooden butts and pistol grips. It was claimed to have cost 5 shillings (25p) to produce in 1944. Anyone who has seen or used it will probably agree that was all it was worth. Around 4 million were produced and issued to the army and Resistance fighters across Europe. It jammed, went off at any time, but it did its job.

It was useful as a clandestine weapon as it broke down into small, easily concealed pieces. These did not resemble any weapon system the Germans used or knew and were often passed over in searches. Apparently, the Germans did not believe such a badly finished poor quality piece would qualify as an issue weapon. However, it was such an innovative design, that the Germans eventually copied it!

The Russians took SMGs to heart and produced millions. Whole divisions were armed with them. This was the PPSh (Pistolet Pulemyot Shpagina), known to the US Army in Korea as the Burp Gun from its distinctive sound. It was equipped with either a 32-round box magazine (rarely) or a 71-round drum magazine. The Germans loved it too and used it whenever they could.

Post-war, a major design change took place: most of the block now surrounded the barrel. Putting the magazine in the pistol grip like an automatic pistol shortened a short weapon even more. The first weapon to incorporate this change was the Israeli Uzi - the basic idea has been copied many times. The Ingram SMG went a step further and replaced the solid block with a pressed steel block, adding weight to it to reduce the rate of fire.

Beginning of the End

The development of the intermediate round - something between a rifle and pistol round - by the Germans spelled the beginning of the end for the military SMG. The first assault rifle was the MP44, renamed Sturmgewehr (assault rifle) in 1945. It had all the features of the SMG, but had better range (up to 300m) and better stopping power.

What with the vast quantities of SMGs produced before 1945, it took some time to replace all the SMGs, but there are few left now. The sub-machine gun still has uses in military, internal security and police work. The Heckler-Koch 9mm MP5 (or HK 54), for example, is used by many police and special service units worldwide and has a good reputation for safety. Despite this, the bulk of the world's armies now use assault rifles.