The LUSA submachine gun line emerged during the early 1980s though never found widespread use with its compact, repeat-fire services. It instead became the weapon-of-choice for some special forces groups, security firms, and private protection services who required a product of this type. The weapon was of a sound design, incorporating proven concepts seen in contemporary guns of the period and was chambered for the readily available 9x19mm Parabellum German pistol cartridge. Its dimensions were handy with a stock-extended length of 23 inches, a collapsed length of 17.8 inches, and a barrel measuring just 6.3 inches long.
Development of the LUSA as an indigenous Portuguese firearm was aided by the fact that Portugal began local, license production of West German Heckler & Koch firearms in the early 1980s. This meant that the required machinery and production process for the weapons could now be reviewed by Portuguese engineers and reconstituted for indigenous design purposes. A compact submachine gun form was then devised and this became the LUSA - named after the ancient Roman territory of "Lusitania" falling within modern Portuguese borders. Manufacture of the weapon came from INDEP (Industrias Nacionas de Defesa, EP) beginning in 1983.
On the whole, the weapon was of a practical arrangement though utilizing a noticeably deep "double-cylinder" receiver. Other facets were conventional such as the angled pistol grip with trigger unit and forward-set magazine well. The short barrel allowed for minimal protrusion at front and iron sights were fitted at front and rear over the receiver in the usual way. The tubular stock was collapsible with aided in compactness and concealability. The magazine well accepted 10-, 18, or 28-round straight, detachable box magazines and also doubled as a forward grip. Internally, the magazines featured a double-stacked cartridge arrangement compressed by a spring for cheap mechanical functionality when feeding the weapon. Overall weight was 6.17lbs and rate-of-fire was 900 rounds per minute. The weapon eventually supported laser aimers and a suppressor for precision and clandestine work respectively. This would appeal to more discerning customers such as special forces operatives.
Upon closer observation, the trigger unit and pistol grip largely resembled that of the German HK MP5 submachine gun line. A fire selector lever allowed for the usual selection choices for this class of gun and, again, mimicked the large, visually-oriented levers encountered with HK firearms. The deep "double-cylinder" receiver was brought about because of the bolt and barrel taking situated in the lower section leaving the mass of the bolt overhang and return spring to be fitted overhead. The sliding stock then slid into the valley created by the over-and-under cylinders.
The weapon was adopted in limited fashion through a first-production model as the "LUSA A1". Two sub-variants of this mark were then made, one with a nut-secured barrel and the other with a fixed barrel shrouded by a perforated barrel jacket to help with cooling and, indirectly, with accuracy by producing a heavier frontend. The "LUSA A2" then appeared in 1991 and retained the same form and function as the A1 but introduced an improved construction process that, in turn, begat a weapon that was both lighter of of more compact dimensions than the original. In 2004, INDEP sold its LUSA equipment to buyers in the United States who went on to form LUSA USA. The weapon was then remarketed and resold under the new brand across the American civilian, police, and military markets as well as for foreign delivery. It also saw several well-accepted chamberings introduced.