In 1964–1966, the designers of the German arms manufacturer Heckler & Koch in Oberndorf am Neckar developed the 9 mm Luger submachine gun based on the G3 assault rifle system, which, unlike most weapons of this category, fired from the front position of the semi-locked breech. The weapon was designated MP5 (Maschinenpistole 5) and became the basis for a large range of variants, differing in design but also in calibre. The MP5 series of submachine guns became widely used due to their operational reliability and accuracy and are still considered the gold standard for judging other weapons in this category. The armed forces, police departments and special units of more than 40 countries have incorporated them into their armament. In 1974, Heckler & Koch introduced a variant with an integrated silencer, designated MP5 SD, where the additional letters stood for silencer in German (Schalldämpfer). The MP5 series submachine guns are still used by special units of the Czech Armed Forces and the Czech Police, including the MP5 SD versions.