The LRDG was a reconnaissance and raiding unit of the British Army, founded in Egypt in June 1940. Because its members were experts in desert navigation, they were sometimes assigned to guide other units – including the Special Air Service – across the desert.
The SAS was formed in July 1941 and originally called "L" Detachment, Special Air Service Brigade. The "L" designation was a ploy, intended to deceive the Axis into thinking there were several such units. According to Wikipedia, "Its first mission, in November 1941, ... was a disaster; 22 men, a third of the unit, were killed or captured. Its second mission was a major success. Transported by the Long Range Desert Group, it attacked three airfields in Libya, destroying 60 aircraft with the loss of 2 men and 3 Willys MB. In September 1942, it was renamed 1st SAS, consisting at that time of four British squadrons, one Free French, one Greek, and the Folboat Section." (The Folboat Section would evolve into the Special Boat Service, or SBS – the SAS's sister force in the Royal Navy.)
The LRDG was disbanded at the end of World War II. According to Wikipedia, "The only comparable British Army units today are the Mobility troops of the Special Air Service." So the LRDG was a forerunner of the SAS, in the sense that it carried out similar operations; but it would not be correct to infer that the SAS had evolved directly from the LRDG.
A bit of a pointless question really (IMHO): slightly misleading – and in any case, what else could the answer be? It just smacks, to me, of someone trying to show off how much they know about military history.
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