The unit was founded during 1959, as an additional regiment of the Territorial Army of the United Kingdom, and was created from the former Reserve Reconnaissance Unit, this unit having originated from an organisation known as Military Intelligence 9. The initial headquarters location was London, the headquarters were moved during 1959, to Thorpe Street, Birmingham, during 1966, to Kingstanding, Birmingham, within a Territorial Army centre. The regiment's first commander was H. S. Gillies, at the time a Lieutenant Colonel. Anthony Hunter-Choat OBE was the commanding officer of the regiment from 1977 to 1983. Sebastian Morley, at that time a Major, was for a period commander of D squadron until his resignation sometime during 2008. During 1963, members of the regiment were deployed to Borneo to support Malaysian and British Commonwealth forces, in combating guerrillas crossing from Indonesia to the federation of Malaysia. By January 1991, 15 volunteers from 21 and 23 SAS joined more than 300 regular SAS soldiers participating in the Gulf War. During mid-October 2001, members of 21 SAS and 23 SAS were deployed to Afghanistan as reinforcements of two squadrons of 22 SAS, for Operation Determine, during the 2001 coalition invasion of Afghanistan to topple the Taliban regime and destroy and dismantle al-Qaeda in the aftermath of the September 11 attacks. Following the invasion, members of the 23 remained in the country to provide close protection to individuals of the Secret Intelligence Service. During June 2008, three soldiers from 23 were killed by the explosion of a landmine their vehicle had triggered, while they were within Helmand province. The reservists were involved in the training the Afghan National Police, during the War in Afghanistan , there were also elements of the Regiment performing tier 1 operational duties during this period, within Iraq. Post Afghanistan, a report found that the SAS lacked a clearly defined role. An inquest into the deaths of three reservists during a test march in 2013, heard that: 6 months' preparation is needed before undertaking "Test Week"; it is possible for "direct civilian entry" students to attempt to join one of two SAS Reserve regiments; and approximately 10% of candidates who took part in the march had had no previous military experience before opting to attempt to join the regiment. An Army review found that though reservists 23 SAS had well-defined jobs during the Cold War, since then "the requirement for them appears to be less clear and more difficult to articulate" and that reservists "were not trained and conditioned to the right level; neither did they have the experience to face the rigours of the test march". During 1 September 2014, 23 SAS was placed alongside 21 SAS under the command of 1st Intelligence Surveillance and Reconnaissance Brigade which provides combat specialist support to the British Army's Reaction and Adaptable Forces. As of 2020 both 23 SAS and 21 SAS are no longer under 1st Intelligence Surveillance and Reconnaissance Brigade and instead an integrated part of United Kingdom Special Forces.
