Its traditional building forms made a significant contribution to the vernacular revival architecture associated with the Arts and Crafts Movement, and would exert a lasting influence. The prominence of Surrey peaked in the 1890s, when it was the focus for globally important developments in domestic architecture, in particular the early work of Edwin Lutyens, who grew up in the county and was greatly influenced by its traditional styles and materials. The late 19th and early 20th centuries saw the demise of Surrey's long-standing industries manufacturing paper and gunpowder. Most of the county's paper mills closed in the years after 1870, and the last survivor shut in 1928. Gunpowder production fell victim to the First World War, which brought about a huge expansion of the British munitions industry, followed by sharp contraction and consolidation when the war ended, leading to the closure of the Surrey powder mills. New industrial developments included the establishment of the vehicle manufacturers Dennis Brothers in Guildford in 1895. Beginning as a maker of bicycles and then of cars, the firm soon shifted into the production of commercial and utility vehicles, becoming internationally important as a manufacturer of fire engines and buses. Though much reduced in size and despite multiple changes of ownership, this business continues to operate in Guildford. Kingston and nearby Ham became a centre of aircraft manufacturing, with the establishment in 1912 of the Sopwith Aviation Company and in 1920 of its successor H.G. Hawker Engineering, which later became Hawker Aviation and then Hawker Siddeley. During the Second World War a section of the GHQ Stop Line, a system of pillboxes, gun emplacements, anti-tank obstacles and other fortifications, was constructed along the North Downs. This line, running from Somerset to Yorkshire, was intended as the principal fixed defence of London and the industrial core of England against the threat of invasion. German invasion plans envisaged that the main thrust of their advance inland would cross the North Downs at the gap in the ridge formed by the Wey valley, thus colliding with the defence line around Guildford. Between the wars Croydon Airport, opened in 1920, served as the main airport for London, but it was superseded after the Second World War by Heathrow, and closed in 1959. Gatwick Airport, where commercial flights began in 1933, expanded greatly in the 1950s and 1960s, but the area occupied by the airport was transferred from Surrey to