 The London Defence Scheme was announced in Parliament in March 1889 by the Secretary of State for War, Edward Stanhope, by which time the 13 sites for the Mobilisation Centres had already been purchased at a cost of £25,000.The London Mobilisation Centres were built along a 70-mile (113-kilometre) stretch of the North Downs from Guildford to the Darenth valley and across the River Thames in Essex.Thirteen sites were chosen, at Pewley Hill, Henley Grove, Denbies, Box Hill, Betchworth, Reigate, East Merstham, Fosterdown, Woldingham, Betsom's Hill, Halstead, Farningham and (to the north east of London) North Weald.