PDW

A personal defense weapon (PDW) is a class of compact magazine-fed, self-loading, firearm – essentially a hybrid between a submachine gun and a carbine, retaining the compact size and ammunition capacity of the former while adding the stopping power, accuracy and penetration of the latter. Most PDWs fire a small-caliber, high-velocity bottleneck cartridge, resembling a small or short rifle round. This gives the PDW better range, accuracy and armor-penetrating capability than submachine guns, which fire pistol-caliber cartridges.

The name describes the type's original role: as a compact but powerful defensive weapon that can be carried by troops behind the front line such as military engineers, drivers, artillery crews or signallers. These soldiers may be at risk of encountering the enemy, but rarely enough that a long-barrel weapon would be an unnecessary burden during their normal duties. Because of their light weight and controllability, they have also been used by special forces and by heavily-armed police.

In the 19th and early 20th centuries, shortened versions of the infantry rifle were issued as 'carbines' for cavalry troops and gun crews. This designation was dropped as infantry rifle designs were shortened, such as in the Short Magazine Lee–Enfield rifle. Thereafter, pistols were typically issued as a self-defense weapons. However, they were not effective in most combat situations. As a result, during the First World War, the Mauser C96 and artillery versions of the Luger pistol were issued with attachable shoulder stock holsters, which allowed for greater control and accuracy.

During World War I, the United States secretly developed the Pedersen device attachment for the M1903 Springfield rifle that allowed it to fire a .30 caliber (7.62 mm) pistol type cartridge in semi-automatic mode. This attachment was developed to allow an infantryman to convert "his rifle to a form of submachine gun or automatic rifle" in approximately 15 seconds.

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