British hid tanks as trucks and faked dummies to fool Rommel

Before the Second Battle of El Alamein in 1942, the Allies needed Rommel's forces to be wrong about both when and where Montgomery's attack would come. Simple concealment — hiding real tanks and matériel from German aerial reconnaissance — has an inherent flaw: German reconnaissance had already mapped where Allied armor was massed, so if that armor simply vanished from photographs, the sudden absence would itself read as a signal that an attack was imminent from that sector, defeating the concealment's purpose.

The Middle East Command Camouflage Directorate under Geoffrey Barkas, working to a deception plan devised by Dudley Clarke, solved this with a double substitution rather than simple concealment. Real tanks in the north, where the actual attack would come, were disguised as ordinary supply trucks — visually present, but registering as harmless logistics rather than armor. Simultaneously, dummy tanks were erected in the positions the real tanks had just vacated, so aerial reconnaissance kept counting the same number of 'tanks' in the same places, even though the real armor had moved.

Disguised real tanks as trucks and put dummy tanks in their old positions, so the aerial picture stayed identical to the enemy's baseline and gave no anomaly to notice.

German reconnaissance had mapped Allied armor, so a sudden gap would signal an attack.

Disguising real tanks as trucks removed them from the tracked 'armor' category.

Dummy tanks in vacated positions kept the count and location of 'tanks' unchanged.

No anomaly in the aerial picture meant no reason for German analysts to investigate.

When hiding a change from someone with a baseline, fill the gap with a decoy so the picture stays consistent.

After the battle, captured German general Wilhelm Ritter von Thoma told Montgomery he had believed the Allies possessed at least one more armored division than they actually had and expected the main attack to fall in the south, while Rommel's deputy Georg Stumme believed the offensive would not begin for several weeks — the deception achieved surprise on both dimensions it targeted, and Winston Churchill publicly credited the camouflage operation when announcing the El Alamein victory in the House of Commons.