Operation Sentinel (1942) was a deception plan used to try and mislead Rommel in believing that Egypt was more strongly defended than it really was during his advance into Egypt after the battle of Gazala.
After the battle of Gazala (26 May-14 June 1942) the Eighth Army was forced to retreat back into Egypt, closely followed pursued by Rommel's forces. The retreat was eventually stopped at the First battle of El Alamein (1-27 July 1942), where a combination of General Auchinleck's skilful handling of his forces and Axis exhaustion saw Rommel's advance finally come to a end. Both sides then settled down to wait for reinforcements. Auchinleck expected Rommel to attack as soon as his army had recovered from the advance into Egypt, and wanted to delay him as long as possible. One of the methods he chose was deception. His Director of Camouflage, Major Geoffrey Barkas, had already developed a collection of dummy tanks, trucks and guns, and he was now ordered to rush them west into the area between El Alamein and the Nile Delta.
Within three weeks Barkas had created dummy installations large enough to simulate two full motorised divisions. At its centre were a series of false camps, which included active kitchens and incinerators, to provide signs of activity, dummy trucks, guns and even dummy drivers. A handful of real troops were used to move around the camps, creating new tire tracks and other signs of life. Amongst the dummies in use was a field gun kit, small enough for an entire battery to be carried in a single lorry. The impact of Sentinel is hard to judge, but Rommel didn't launch his next offensive until 31 August (battle of Alam Halfa), by which time the first Allied reinforcements were reaching the front.
Operation Sentinel took place alongside Operation Cascade, a more intelligence led operation that created a whole series of dummy units
After Auchinleck had been replaced by the team of General Alexander and General Montgomery Operation Sentinel was followed by Operation Bertram and Operation Treatment, a pair of linked operations designed to convince Rommel that any offensive in the Western Desert wouldn't start in November, and that it would hit the southern part of the German line, and not the northern end, where Montgomery actually intended to attack. Operation Cascade also continued under Montgomery, and these deception operations probably played a significant part in the Allied victory. The Germans were certainly caught out by the timing of the Allied attack, and kept half of their armour in the south for the first few days of the battle.