At the start of the Second World War, and during its early stages, it was the ideas and initiatives of these amateur soldiers which led to the creation of at least two units within the Special Forces and gave a particular elan to others.

Luckily the modern SAS looks safe from this danger; it is constantly experimenting with innovative techniques, many of which stem from its Territorial regiments, drawn as they are from every walk of civilian life.

The role of the SAS in the defence of West Germany was kept top secret but by the 1960s, the KGB and East German intelligence were well aware of what was being planned and even tried, unsuccessfully, to penetrate the unit.

[11] Peter de la Billiere, who later commanded 22 SAS and then became Director Special Forces, served as the adjutant of 21 for part of this period.

[18][19] On 1 September 2014, 21 and 23 SAS were moved from United Kingdom Special Forces and placed under the command of 1st Intelligence, Surveillance and Reconnaissance Brigade.