As the Panzers of Rommel's Afrika Korps swept the British back into Egypt in 1941, a young commando lieutenant, David Stirling, persuaded his superiors to allow him to set up a special deep-penetration unit which could cause havoc behind enemy lines. Its first mission was a disaster but soon Stirling and the mavericks he had gathered proved that they had a valuable covert role to play.

After its initial and near-fatal problems the SAS changed its tactics - using its own heavily-armed jeeps to strike deep behind enemy lines attacking German and Italian airfields and supply lines. By the time the fighting in North Africa ended, the exploits of the unit were fast becoming legend - but it had lost its founder and was again struggling to survive.

As the Allies landed on D-Day to begin the liberation of Europe, the SAS used the skills it had honed in the desert in this new theatre of war. On the night before the landings, teams were parachuted in to create havoc and distract the German defenders. Then the armed jeeps ranged deep behind the enemy's lines attacking reinforcements and communications.

As the Allies broke out of their Normandy beachhead and swept towards the German border, the SAS continued its deep penetration role. But the regiment was also called on for other vital tasks - tracking down Hitler's mobile and elusive V-2 rocket launchers, and then hunting the Nazi war criminals that had killed members of the SAS in cold blood.

After World War II the SAS was disbanded, but it was soon realised that its special skills would be needed in the volatile post-war situation. The regiment was clandestinely rebuilt and undertook a variety of secret missions. Then in 1981 it hit the headlines when terrorists holding hostages in the Iranian Embassy were swiftly and successfully eliminated and their captives freed.

When the British Task Force sailed to take back the Falkand Islands from Argentine occupation, two squadrons of the SAS went with it. Over the next few weeks they were involved in a variety of surveillance missions, and a vital and brilliantly executed raid on an Argentine airstrip on Pebble Island which effectively eliminated all enemy air power on the Falklands.

In the Gulf wars of 1992 and 2003, the SAS returned to its roots as deep penetration teams fanned out into the Iraqi desert. Their missions ranged from disrupting supply lines and communications and raiding airfields, to the vital task of tracking down Saddam Hussein's Scud missile launchers which were being used to deadly effect and threatening to destroy the coalition against him.