The SAS or Special Air Service is an elite unit of the British Army. It was formed as a regiment in 1941 as a regiment. In 1950 it became a corps. 

The SAS has been elevated in popular culture to an almost mythical elite unit. They became internationally renowned during Margaret Thatcher’s term as Prime Ministers after the televised rescue of hostages held during the 1980 Iranian Embassy terrorist siege.

The SAS is based in Hereford and specialises in hostage rescue, counter-terrorism, covert reconnaissance and direct action. 

The unit is formed of the 22nd Special Air Service Regiment, the reserve units 21 Special Air Service Regiment and the 23rd Special Air Service Regiment. The Royal Navy has a similar unit called the SBS or Special Boat Service which deals with maritime counter-terrorism. 

The SAS is classified top secret and it is difficult to give much information about them as it is all highly classified.