To add to what the others have said about the Special Air Service, it was put together by Major David Sterling as a unit to operate behind enemy lines for extended periods, obeserve enemy strength and activity, and to conduct interdiction and limited harrassment on a "hit-and-run" basis. The name Special Air Service was indeed selected as a ruse, but it stuck. Major Stirling designed the unit cap badge, a Fairbairn dagger with the motto "Who Dares, Wins".
Early operations were conducted on poorly-equipped vehicles that were on hand, then the SAS procured some 3/4 Ton and 1.5 Ton Chevrolet commercial trucks of pre-war design that they extensively modified, cutting away the doors and cab roof, most of the vertical grille in front of the radiator, etc. They also fitted cargo beds to which were fastened sections of perforated metal airstrip decking which they used to help get unstuck from soft sand. Low pressure wide unidirectional tires were fitted on special rims to reduce the specific pressure on the sand. Some vehicles were fitted with .30 M1919 and .50 caliber M2 Browning machine guns on flexible mounts. Supplies were typically carried for missions lasting betw. three days to two weeks and even longer.
Personnel volunteered from much of the Empire -- there were British, Australian, Canadian, and New Zeeland soldiers under Sterling's command, so many that specific SAS units (Squadrons) were formed almost entirely with personnel from a specific country.
The Bantam/Willys/Ford Jeep came a bit later in SAS operations in the North African campaign, and again the grillwork was cut away, extra fuel tanks fitted, MGs on flexible mounts, etc. Jeep-embarked patrols would operate singly on occasion, but with groups of two to four vehicles being more common. In fact, the North African exploits of the SAS were the inspiration for the '60s TV series "Rat Patrol" that each week were a PITA to German character actor and all-around bad guy Eric Braeden.
Today, the SAS (tan berets with Who Dares Wins dagger badge) are one of the elite British forces, together with the Royal Marines' Special Boat Service (SBS) and Mountain and Arctic Warfare Cadre (M&AW)units and certain independent units of the Parachute Batallion (Paras).
BRS