Outer London Defence Ring

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The Outer London Defence Ring was a defensive ring built around London early in the Second World War to stop a German invasion. It was part of a wider system called Stop Lines. In June 1940, under General Edmund Ironside, rings of anti-tank defences and pillboxes were built around London: the London Inner Keep, London Stop Line Inner (Line C), London Stop Line Central (Line B), and London Stop Line Outer (Line A). The Outer Ring was the strongest because it could be built in open countryside. Work was halted a few weeks later when Ironside’s successor, General Alan Brooke, favored mobile warfare over static defence. The ring used a mix of natural rivers and artificial ditches up to 20 feet wide and 12 feet deep to encircle London. North of the city, the line followed a route similar to the modern M25, from Watford along the River Colne through Potters Bar, Cuffley, Nazeing, then south through Epping Forest, Loughton and Chigwell. Many pillboxes and anti-tank traps can still be seen, though in many places the ditch is now hidden by the M25 or by suburbs.