List of British deception formations in World War II

During the Second World War, the British Army made extensive use of fictional formations as part of various military deception efforts to inflate their order of battle. The use of such formations was pioneered by Lieutenant-Colonel Dudley Clarke, based within the Mediterranean and Middle East theatre, and later joined by colleagues located in the UK. The initial efforts were small and created a fictional brigade with no long-term goal. As the war progressed, the deception efforts escalated into elaborate plans that included entire notional armies. In total, 36 notional divisions were created although they were not all employed at the same time. Some of these were based on real units that had previously been disbanded.

Clarke's initial order-of-battle deception created the 1st Special Air Service Brigade. This notional formation was aimed to take advantage of Axis fears of British paratrooper forces being based in Egypt, from where they could potentially land behind the front line. It was followed by two separate efforts that created fictitious divisions to hide various weakness of the British forces in the theatre. In 1942, these efforts grew into Operation Cascade, which again sought to hide the weakness of British forces and deter potential Axis aggression.

In 1943, planning began for the Allied reconquest of German-occupied Western Europe. A major deception effort, Operation Bodyguard, was implemented and included forces based within the UK and the Mediterranean. Allied staff based in the UK worked on Operation Fortitude, which aimed to create new fake formations and an entire notional order of battle. The goal of these efforts was to lead the German military into believing substantial forces could attack Norway, and that Normandy landings were a ruse to hide the real attack that would be launched elsewhere by notional forces based in the UK. Within the Mediterranean theatre, Operation Zeppelin was Fortitude's counterpart. It aimed to elaborate on the work undertaken by Operation Cascade and use the notional formations to feign the threat of attacks throughout the Mediterranean area. The fake order of battle was also used to conceal troop movements from the Mediterranean to the UK. While fake divisions were created to supplement Allied forces in British India and Burma, there was no theatre-wide deception effort.

These various deception operations undertook administrative and physical efforts to fool Axis forces into believing these formations existed. This included fake insignia and documents, inflatable tanks, wireless communications, and the deliberate leaking of information, especially via double agents. Within Europe, these efforts convinced the German military that the Allied powers had more divisions than they did. However, similar efforts in Asia were met with mixed success.