SAS is an acronym for the Special Air Service Regiment of the British Army. Established during World War II, it served as the model for many of the world's current special forces units. It is an elite unit comprised of a select few, excelling at covert reconnaissance and sabotage in enemy territory. Its motto is "Who Dares, Wins".

The Boss, who is regarded as the mother of all special forces units, once served in the SAS, as did Major Zero, the commander of FOX. It was this prior relationship that led Major Zero to recruit her for the Virtuous Mission. Other former members of the SAS include McDonell Miller, FOXHOUND's survival expert, and Liquid Snake, who took part in the Gulf War in his teens.