Despite its strategic industries (rail and aero-engine), Derby suffered comparatively little damage in both world wars (contrast Bristol and Filton). This may in part have been due to the jamming of the German radio-beam navigations systems (X-Verfahren and Knickebein), camouflage and decoy techniques ('Starfish sites') were built, mainly south of the town, e.g. out in fields near Foremark.