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.

Lieutenant-Colonel Dudley Clarke, who had previously been engaged in various intelligence work and had helped form the Commandos, was assigned to Middle East Command on 19 December 1940. His role was the Personal Intelligence Officer (Special Duties) to Middle East Command's commander-in-chief, General Archibald Wavell. After assisting with Operation Camilla, the deception plan for the reoccupation of British Somaliland, Clarke undertook his first effort to create an entirely fictitious formation.

Operation Abeam was the codename given for the creation of the fictional 1st Special Air Service Brigade. This brigade was placed to notionally support Wavell's attack against Italian forces in the Western Desert campaign, by playing on the Italian concern of potential British airborne forces being in the theatre and that they could be used to land behind the frontline. This was followed by a scaled-up version, in efforts to fool Italian intelligence into believing that a notional 10th Armoured Division was arriving piecemeal in Egypt, where British forces were based. The plan aimed to cover the lack of British armoured forces actually located there.

The first use of deception formations within combat plans came shortly thereafter, in March 1941, when Wavell planned to seize the island of Rhodes. A deception plan was formed to suggest the real target was Scarpanto and that the 1st Special Air Service Brigade would raid Rhodes to distract Axis forces. Due to German reinforcements arriving in Africa, to bolster the Italians, the attack did not occur. On 28 March, Clarke's team became known as Advanced Headquarters 'A' Force, with the 'A' purposely left ambiguous.

Abeam and the 10th Armoured Division had been intended only for short-term use, the first long-term plan was formed in June. Cyprus was potentially at risk of invasion, following the German occupation of Crete. The Cyprus Defense Plan aimed to deter any attack and to buy time to allow actual reinforcements to arrive to bolster the 4,000-man garrison. The deception plan claimed that the garrison was at least 20,000 strong, based around the fictitious 7th Infantry Division (Cyprus). The plan evolved to include additional units, a changing order of battle for the 7th Division, and a notional corps headquarters. These successes prompted the creation of the London Controlling Section, a similar unit to 'A' Force but based in the UK.