The SAS is facing a recruitment crisis because soldiers do not have time to train for demanding selection tests, the head of the infantry has warned.
The Special Air Service (SAS) has a history of tackling perilous engagements, their most famous being carried out in the full glare of television cameras in 1980, when they stormed the Iranian embassy in London, where armed men from the Arabic-speaking province of Khuzestan had killed a hostage.
The SAS freed the remaining hostages and killed five of the six gunmen, although their spectacular success - shown live on television after the BBC broke into coverage of the snooker - gave them much unwanted publicity.
The SAS and its motto, Who Dares Wins, was born early in World War II, when a British army officer, David Stirling, came up with the idea of a highly trained special force which might wreak havoc on enemy supply lines, bases and morale.
He joined forces with an Australian, Jock Lewes, an officer in the Welsh Guards who had a talent for improvisation.
Parachutes were the obvious way of getting troops behind enemy lines, but an early practice jump using a scrounged parachute and an unsuitable aircraft put Stirling in hospital for two months.
He used the time to flesh out his plan, and on leaving hospital, he slipped past the guard at High Command headquarters, and managed to convince the top brass that his idea was both necessary and feasible.
The SAS was initially created as a desert raiding force to weaken Rommel's North African logistics network as well as hinder aircraft operations.
Their first successful raid was in December, 1941, when two groups destroyed 61 aircraft at two airfields.
There were to be many more SAS operations in the war against Hitler and later, the SAS saw action in several counter-insurgency operations, in Oman, Aden, Malaya and Borneo.
They were also deployed in Northern Ireland, where they carried out several deadly ambushes against IRA men. They have subsequently been accused of "breaking the rules of war" by relatives of some of those killed, who claimed the SAS shot dead survivors instead of taking them prisoner.
In 1988 the SAS shot dead three members of an IRA "active service unit" in Gibraltar in what was to become a highly controversial incident.
The government attempted to prevent an ITV documentary, Death On The Rock, being broadcast. The programme alleged no warning was given by the SAS team and no attempt made to detain the IRA gang.
The SAS also saw intensive action in the Falklands.
Bravo Two Zero
During the Gulf War, SAS teams penetrated deep within Iraq to search for mobile Scud missile launchers.
But the experiences of one eight-man team illustrated how the courage and reputation of the elite force could not guarantee success.
After being dropped far behind Iraqi lines, three men were killed and four captured, although they are said to have first killed 250 Iraqis.
A book taking its title from the team's call sign, Bravo Two Zero, made a fortune for its author Andy McNab, a pseudonym of the group's leader.
It has sold 1.5 million copies, been translated into 16 languages, and spawned dozens more books about the SAS, to the consternation of those whose lives could depend on the secrecy of its methods.
The men of the SAS have known hardship before they ever join. The selection process is, as one might expect, gruelling. Probably the most testing element is the Long Drag.
It is a 40-mile trek over the Brecon Beacons, carrying a 55-pound backpack, that does not include the required food and water. Only about one in every 12 soldiers passes the course.
The SAS cap badge depicts not a winged dagger, as was thought, but King Arthur's sword, Excalibur, surrounded by flames.
British special forces were deployed in Afghanistan after the attacks on the Twin Towers and the Pentagon on 11 September 2001.
There they ended up fighting men who the SAS had helped to train.
According to one former SAS man, Mujahideen fighters loyal to Osama Bin Laden were trained by the SAS in the 1980s as part of the West's efforts to bolster resistance to Soviet forces.
The British are said to have taught the Afghans how to use deadly Stinger missiles, capable of bringing down helicopter gunships.
SAS troops are thought to have helped guide precision air strikes and attacked al-Qaeda camps in Afghanistan. A special SAS unit was engaged in mountain training in Pakistan for several years.
The SAS are also believed to have been involved in Iraq following the invasion in 2003.
They had kept a lower profile in recent years.
But in March 2011 the SAS suffered one of the most embarrassing incidents in their history.
Six SAS men and two Foreign Office officials were dropped by helicopter in Libya after the uprising against Colonel Gaddafi.
They were apparently under orders to contact the rebel leadership but they were disarmed and detained for two days by rebels in eastern Libya and then unceremoniously kicked out of the country.
The incident was a huge embarrassment for the Foreign Office and, although the full story has not yet come out, it put a considerable dent in the SAS's reputation.