Purpose of the SAS mod is to give a completely new look at SWAT 4 fixing, where possible, the main game bugs and introducing new features. The SAS mod improves SWAT 4 gameplay looking at weapons, equipments and tactics of the real 22nd SAS Regiment.
The ARWEN 37 is a non-lethal launcher which fires 37 mm non-lethal rounds (foam or wooden or tear gas payload) designed for riot control. It has a 5-round rotary drum magazine. "ARWEN" is an acronym for "Anti Riot Weapon ENfield".
It was designed in 1977 by the British Royal Small Arms Factory (RSAF) Enfield, then part of the Royal Ordnance Factories. It came out of a British Military request for a multi-shot riot control weapon. Three prototypes were designed and tested: one semi-automatic, one rotary-drum, and one pump-action. At the end of testing the rotary-drum model was put into production. The case has a rebated rim, so although the projectiles are comparable with other 37mm riot control weapons, the loaded rounds are quite different.
As of 2001, all ARWEN trademarks and patents are owned by Police Ordnance Company Inc. The weapon is manufactured under license in Canada.
Quote from Wikipedia.org