In Another Job for Biggles, El Moab was a farm in the Danakil desert where Nicolo Ambrimos grew hemp for hashish, and later, gurra, a potent narcotic plant which had been transplanted from Wadi al Arwat. Near El Moab was Aerodrome 137, an abandoned landing ground used by the R.A.F. during the war which Biggles used as a rendezvous. Biggles and Ginger were, for a time, kept prisoners at El Moab when they were captured by Ambrimos' men. They were later rescued by Bertie and Zahar.
El Moab was set in a wadi. A dam built across the a gorge at one end of the wadi ttrapped rain water and created a large lake which was used to irrigate the crops. From this dam a small stream flowed through the farm. Hashish and gurra was grown in El Moab. Most of the narcotics produced travelled by camel to the coast to be smuggled out by dhows but some were flown out in a De Havilland Gipsy Moth operated by Ambrimos.
El Moab was largely destroyed when Bertie, acting on the orders of Biggles, blew the dam up with dynamite. The resulting flood waters swept through the farm, eliminating the crops. Many of the hashish growing gang drowned, including, it was believed, Ambrimos himself.
While the text drops tantalising hints about the location of El Moab, these are far from clear and somewhat contradictory. Zahar tells Biggles that El Moab is about two day's march (about forty miles) inland from the Red Sea coastal port of Mersa Mekel (a fictional location). Biggles speculates that this might put the place in Ethiopia, which is plausible. Later Biggles tells his Ginger and Bertie that El Moab might be in Ethiopia or Sudan, he was not sure which. It is extremely unlikely that El Moab could be in Sudan. The Sudan Red Sea Coast is too far to the north of Aden and that region does not share a border with Ethiopia within forty miles. What Biggles probably meant was Eritrea--this was formerly an Italian colony and came under British administration after World War 2 until Eritrea became independent in 1952.
Within the Southern Red Sea region of Eritrea, El Moab is unlikely to lie to the south near the Djibouti border. In flying to El Moab, Biggles chose not to cross the Red Sea at the nearest point, which would have been at Djibouti. Instead he flew northwest along the coast of Yemen for a while to avoid observation by Ambrimos' spies. Near to the Djibouti border is the Ertitrea port of Assab, which was quite developed even in Biggles' time. If El Moab had been inland anywhere near there, Biggles and Zahar could hardly have failed to notice it or use it as a navigation landmark. Instead, they searched for Mersa Mekel, which was described as a only a few shacks, mostly in ruins. This must lie further to the north.