'Harley Street' was a British one of a series of a tactical reconnaissance deceptions in Belgium by Lieutenant Colonel David Strangeways’s R' Force designed to capture intelligence and at the same time confuse the Germans about the main axes along which the formations of General Sir Bernard Montgomery’s 21^st Army Group were likely to advance (October 1944).

Other components of this undertaking included 'Housekeeper' (ii), 'Inclination', 'Infatuation', 'Mainstay' and 'Warhorse'.

'R' Force was a British deception force comprising armoured vehicles, field engineers and a wireless unit. During 'Fortitude', in the period leading to 'Overlord', it attempted to exaggerate the strength of Allied forces in the UK and to deceive German intelligence about Allied intentions, and later it performed a similar role during the fighting of 1944/45 in North-Western Europe.

Strangeways, the 'R' Force' commander, had served in the North African campaign with Brigadier Dudley W. Clarke’s 'A' Force, a special unit that used radio nets to disseminate false information, and decoy tanks and other vehicles to divert Axis forces away from the areas of Allied attack. In the last days of the campaign, Strangeways used a combination of bluff, boldness and speed to seize the German headquarters in Tunis before the Germans could destroy their secret documents.

In 1943, after Montgomery took command of 21^st Army Group, he requested that Strangeways take charge of another deception force organised along the lines of 'A' Force for service in the Allied invasion of France. Strangeways chose the name 'R' Force in the hope that if the Germans discovered it, they might assume that the R stood for reconnaissance, and the force could indeed operate in this capacity as it was equipped with three companies of light scout cars and a support company. These were equipped with special speakers so they could emulate the sounds of tanks in battle. 'R' Force also assumed command of a number of Royal Engineer camouflage units, and its strength and capability were further boosted by the addition of personnel from Colonel John Turner’s 'Turner’s Department', which been engaged in the construction of decoy airfields and other military sites. No. 5 Wireless Group was formed in January 1944 to provide 'R' Force with a communications deception capability. Equipped with special radios and recording devices, it could simulate the radio traffic of a corps. The strength of 'R' Force eventually pealed at more than 1,200 personnel.

Following the 'Overlord' landings of June 1944 in Normandy, 'R' Force moved to the continent, where it operated under the control of the 21^st Army Group. It was one of the first units to enter Rouen and Brussels, and later undertook a deception campaign for the crossing of the Rhine river.