Somerset is a county in the south west of England. It is a rural county and transport infrastructure has been significant in industrial development. There is some heavy industry particularly related to the defence technologies and the county has several centres for stone quarrying, although the coalfield is now closed. Agriculture and textile production continue to provide employment along with tourism. Industry Somerset has few industrial centres. Bridgwater was developed during the Industrial Revolution as the West Country's leading port. The River Parrett was navigable by large ships as far as Bridgwater. By then loading the cargoes onto smaller boats at Langport Quay, next to the Bridgwater Bridge, they could be carried further up river to Langport. The Parrett is now only navigable as far as Dunball Wharf; and the wharf is still in use today to unload marine gravels and sands. Bridgwater, in the 19th and 20th centuries, was a centre for the manufacture of bricks and clay roof tiles, Bath bricks and later cellophane, but those industries have now closed. With its good links to the motorway system, Bridgwater has developed as a distribution hub for companies such as Argos, Toolstation and Gerber Juice. The Somerset Levels has historically been a large producer of peat, but ecological concerns have led to the search for alternative materials for applications, such as potting of plants. AgustaWestland manufacture helicopters in Yeovil. Helicopters were also built at Weston-super-Mare; it is now the home of a helicopter museum - The Helicopter Museum. Normalair Garratt, who built aircraft oxygen systems, are also based in the town; the company is now part of Honeywell Aerospace. Many towns have encouraged small-scale light industries, such as Crewkerne's Ariel Motor Company, one of the UK's smallest car manufacturers. Defence industries Somerset was, and is, an important supplier of equipment and technology to support the defence of United Kingdom. A Royal Ordnance Factory, ROF Bridgwater was built at the start of the Second World War, between the villages of Puriton and Woolavington, to manufacture explosives; and in 2007 is still operating, at a much reduced output, as part of BAE Systems Land Systems and is due to close completely in 2008. Templecombe has Thales Underwater Systems; and Taunton presently has the United Kingdom Hydrographic Office and Avimo, which became part of Thales Optics. It has been announced twice, in 2006 and 2007, that manufacturing is to end at Thales