As part of U.K. Special Forces Special Air Service (SAS) are British Army personnel who have undergone extensive selection, training, and are most commonly used in operations deep in denied territory.
Their lineage goes back to an organization formed during the North African campaign of the Second World War, under David Stirling. The name refers to attacking German airfields, which they did using ground vehicles; they were not a paratroop formation.
They have long been based at Hereford, although they are reported to have moved the headquarters to Credenhill. 22 Special Air Service Regiment (SAS) is the active army component, and 21 and 23 SAS Regiments in the Territorial reserves; "L" detachment is made up of Territorials on active duty with 22 SAS.
A SAS regiment has a headquarters and four "Sabre squadrons" of approximately sixty men each; the squadrons are further divided into 4 troops. While the troops are cross-trained, there are four specializations within a squadron:
SAS was the model for U.S. Delta Force; COL Charlie Beckwith and others served exchange tours at Hereford.