This was a British disinformation effort to persuade the Italians that the British had deployed airborne forces to North Africa (1941).
The unit at the heart of this deception was the fictitious 1st Special Air Service Brigade. This first saw the light of day in Cairo during 1941 as part of a deception effort by Lieutenant Colonel Dudley W. Clarke designed to exploit the know Italian concerns of airborne attacks on their positions in North Africa. Clarke used a number of means, including documents, photographs, news reports and even fake SAS soldiers, to disseminate false information about this supposed unit. Indeed, he even named his Cairo-based deception department 'A' Force to strengthen the supposed evidence of the brigade’s existence.
In the summer of 1941, when he was advocating his idea for a dedicated airborne commando unit (later the Special Air Service), Lieutenant Colonel David Stirling obtained Clarke’s support partly by promising to use the SAS name. From late 1942, Clarke used the 1st SAS in 'Cascade', his major order of battle deception, as an element of the equally fictitious 4th Airborne Division. Between that time and the end of the war it was used to mislead Axis commanders about the strength of Allied forces in North Africa, and as part of several specific tactical deceptions.
The origins of the 'Abeam' effort lay in the British recovery, late in 1940, of the diary of an Italian officer during an operation at Sidi Barrani. The diary referred to fears of British paratroopers being landed in the Italians' rear areas. At this time the British had no airborne troops in North Africa and Clarke, heading the military deception in the theatre, decided that there could be a major advantage in playing on these fears by creating a fictional airborne unit.
Clarke began 'Abeam' in January 1941 by creating a paper trail for the 1st SAS Brigade, which was, so it was made to see, located in Transjordan while training for special missions. Clarke established the unit’s existence using documentary and physical subterfuge. Photographs of parachutists were printed in local papers, documents were planted where they would be found by the Italians, Allied airmen were warned to watch out for and avoid gliders, of which a number were mocked up to support the story), and a section of desert was cordoned off for 'training'. To aid the rumours, two soldiers were dressed in 1st SAS uniforms and wandered around the Allied-held cities of Cairo, Port Said, and Alexandria, where they were briefed to hint at missions in Crete or Libya.
By March, Clarke’s deception operations had grown and it was decided to create a formal department to plan and implement these. He chose the name Advanced Headquarters 'A' Force, with the capital letter supposedly referring to airborne, in the hope that it would help support the existence of paratroopers in the area and also to conceal the true purpose of his department).
Clarke continued actively promoting the existence of 1st SAS until around June 1941, and it appears that Axis commanders accepted the brigade as real. Clarke had created the unit with no specific aims, although it did mean that the enemy command had to factor the existence of airborne troops into any battle plan. However, 'Abeam' and the 1st SAS represented his first attempt at inflating the apparent strength of Allied forces, a tactic he would use significantly over the rest of the war. The brigade occasionally featured in Clarke’s tactical deceptions including a March 1941 threat to Axis supply lines near Tripoli.
In 1941/42 the 1st SAS was a primary element of Clarke’s overall scheme to deceive the Axis forces in North Africa and the Mediterranean about the strength of Allied forces in the region. Early in 1942 this extemporised effort was formalised as 'Cascade', which was an entirely fictitious order of battle of many formations and units. By a time late in 1942 the Allies had begun to train a number of real airborne units in the North African theatre, and Clarke crafted the 4th Airborne Division out of several units, both real and fictional, including the 1st SAS. 'Cascade' was designed to mislead the Axis forces that paratroopers, most of whom were still under training, in fact posed a realistic and indeed short-term threat. Use of the 4th Airborne Division’s supposed existence was made in a number of specific operational deceptions over the next few years (including 'Zeppelin' and 'Barclay'), most often to create the fictional threat of airborne landings as distractions from real Allied operations.