In a stay-behind operation, a country places secret operatives or organisations in its own territory, for use in the event that an enemy may overrun that territory. If this occurs, the operatives would then form the basis of a resistance movement, or would act as spies from behind enemy lines. Small-scale operations may cover only small areas, but larger stay-behind operations envisage reacting to the conquest of entire countries. The United Kingdom's Territorial Army regiments of SAS and Honourable Artillery Company provided such stay-behind parties in the UK's sector of West Germany.