Major John Woodhouse introduced SAS Selection in 1952. Before that, troopers had earned their credentials in the field.

SAS Selection and Training is the most demanding military training course in the British Army and is also said to be the most demanding in the world: it  has a pass rate of 2-10%. It is a six month test of strength, endurance, and resolve over the Brecon Beacons and Elan Valley in Wales, and in the jungle of Brunei. The Namib Desert is also used as a desert training ground in some circumstances.

SAS selection is held twice a year regardless of weather conditions. Any candidate must be a male and have been a regular soldier in a British Army or RAF Regiment for at least three years, or a member of 21 SAS or 23 SAS (which can be joined directly from civilian life) for at least 18 months. All soldiers who apply should have at least 39 months of military service remaining. A candidate who fails any stage of the selection is 'Returned to Unit' (RTU'd). Candidates are allowed two attempts at passing selection, after which they may never reapply for special forces.

Like other sections of the British armed forces, the SAS accepts members from the Commonwealth, with representation from Fiji, the former Rhodesia, New Zealand and Australia. The Parachute Regiment, Foot Guards and Household Cavalry also provide more recruits than any other regiments. A high number of SAS officers have also been educated at Eton College, probably because of the Guards regiment connection.

Special Forces Briefing Course (3 Days)

This is the first part of selection. It is a joint service three day course to show potential SAS and SBS recruits what is required of them during selection and their career in the Special Forces. Class room lectures and PT, physical training, are frequently done by the recruits. This course must be passed just to get into the real selection phase.

Fitness and Navigation (4 weeks)

The first part of selection is held in the Brecon Beacons and Elan Valley. The weather there can be unpredictable and soldiers have died during selection, due to hypothermia or exposure. The course starts with the Standard Battle Fitness Test, a 2.5km run in under 13 minutes, and then the same distance run alone in under 11½ minutes.

The first week mostly consists of runs in the area, up and down hills with a small bergen. Lessons in navigation and map reading are also included. Navigation runs in small groups in woodland areas and night marches follow shortly. The load in the bergen gets heavier and an SA80 rifle with no slings or straps has to be carried. Soldiers have to keep the rifle in their hands as they climb up the slopes and jog down again.

In the third week navigation is solo from a grid reference to other points on the map. At each rendezvous (RV), the soldiers have to indicate where they are before the next grid reference is given. The soldiers are not told how long the run is and where they will end up. In the last week, there is a race against the clock every day, with each task more punishing as the distances and load of the bergen increase. The "Long Drag" is the last ultimate test - about 60km over the mountains in under 20 hours.

Initial Continuation Training (4 weeks)

This consists of detailed and realistic training in weapons handling, demolitions and small patrol tactics. Those who are not already parachute qualified are also trained in this skill. On completion of SAS parachute training, soldiers are awarded SAS wings, worn at the top of the right sleeve.

Jungle Training (6 weeks)

Soldiers are divided into patrols of four and are watched over day and night by Directing Staff (DS). Soldiers must stand to for one hour at dawn and one hour at dusk every day without fail and must also keep their machete with them at all timesfor safety. After lessons in navigation, boat handling, and jungle and contact drills there is a final test, where all things that have been learned must be demonstrated correctlyto the DS.

Combat Survival (4 weeks)

There is another month of training in survival skills, living off the land and using escape and evasion (E & E) tactics. There are lessons and lectures in interrogation techniques from people who have been Prisoners of War (POWs). The last few days is the E & E stage. In groups the soldiers are dressed in WW2 greatcoats to slow them down, and have to evade capture from the Hunter Force, which is usually comprised of Parachute Regiment or Gurkha soldiers. When captured, every soldier has to withstand tactical questioning (TQ) given by the JSIW (joint services interrogation wing). The soldiers are blindfolded, put in stress positions, subjected to white noise, dehydrated and given no food. The soldiers are only allowed to respond to questions with:

-        Name

-        Rank

-        Number

-        Date of birth

-        "I'm sorry I cannot answer that question ma'am/sir"

In practice, soldiers are also allowed to tell their captors their blood type and previous medical history. Hoever, if they break or disclose any extra information during TQ then they are RTU'd.