BAE Systems plc is a British multinational defence, security, and aerospace company. Its headquarters are in London and Farnborough in the United Kingdom with operations worldwide. The company is the largest defence contractor in Europe and among the world's largest defence companies; it was ranked as the third-largest based on applicable 2017 revenues. Its largest operations are in the United Kingdom and United States, where its BAE Systems Inc. subsidiary is one of the six largest suppliers to the US Department of Defense. Other major markets include Australia, India, and Saudi Arabia, which account for about 20% of BAE's overall sales. It is the biggest manufacturer in Britain. The company was formed on 30 November 1999 by the £7.7 billion purchase and merger of Marconi Electronic Systems—the defence electronics and naval shipbuilding subsidiary of the General Electric Company plc—by British Aerospace, an aircraft, munitions and naval systems manufacturer. ,BAE is the successor to various aircraft, shipbuilding, armoured vehicle, armaments and defence electronics companies, including The Marconi Company, the first commercial company devoted to the development and use of radio; A.V. Roe and Company, one of the world's first aircraft companies; de Havilland, manufacturer of the Comet, the world's first commercial jet airliner; Hawker Siddley, manufacturer of the Harrier, the world's first VTOL attack aircraft; British Aircraft Corporation, co-manufacturer of the Concorde supersonic transport; Supermarine, manufacturer of the Spitfire; Yarrow Shipbuilders, builder of the Royal Navy's first destroyers; Fairfield Shipbuilding and Engineering Company, builder of the world's first battlecruiser; and Vickers Shipbuilding and Engineering, builder of the Royal Navy's first submarines. ,Since its formation it has made a number of acquisitions, most notably of United Defense and Armor Holdings of the United States, and sold its shares in Airbus, Astrium, AMS and Atlas Elektronik. BAE is involved in several major defence projects, including the Lockheed Martin F-35 Lightning II, the Eurofighter Typhoon, the Astute-class submarine and the Queen Elizabeth-class aircraft carriers. BAE Systems is listed on the London Stock Exchange's FTSE 100 Index.