Introduced in 2004, the Brugger & Thomet MP9 became a further development of the Steyr TMP ("Tactical Machine Pistol") originally designed by Austrian-based Steyr Mannlicher and itself introduced in 1992. Manufacturing rights to the Austrian weapon sold to Brugger & Thomet AG of Switzerland and slight variations were added to make for a more modern, marketable product. Key changes included the introduction of a section of Picatinny rail over the receiver (supporting tactical accessories like optics and aimers), a revised trigger safety, and a new hinged, side-folding strut-style shoulder stock.
From this design came a semi-automatic civilian market-minded form in the "TP9".
At its core, the MP9 makes use of a blowback, rotating bolt firing action utilizing a short recoil approach. The cartridge of choice remains the German 9x19mm Parabellum pistol cartridge which the MP9 can be fed from a 15-, 20-, 25- or 30-round detachable box magazine. Rate-of-fire is listed at 900 rounds-per-minute rate-of-fire in the MP9 and TP9 systems while another variant - the MP9-N - fires up to 1,100 rounds-per-minute. Muzzle velocity is 1,315 feet per second with an effective range out to 328 feet meters.
Its lightweight body and compact dimensions have made it a popular weapon among police and special force units as well as some global armies. Operators (as of 2015) include Bulgaria, India, Indonesia, Macau, Portugal, Switzerland, and Thailand. For India, the gun stocks the inventories of Mumbai Police and the Indian Army. Portugal issues the weapon as a sidearm for the Army. Both Swiss police forces and the Army use the MP9.