BAE Systems plc is a British multinational defence, security and aerospace company headquartered in London in the United Kingdom and with operations worldwide. It is among the world's largest defence contractors; it ranked as the second-largest based on applicable 2012 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. The company was formed on 30 November 1999 by the £7.7 billion merger of two British companies; Marconi Electronic Systems (MES) – the defence electronics and naval shipbuilding subsidiary of the General Electric Company plc (GEC) – and British Aerospace (BAe) – an aircraft, munitions and naval systems manufacturer.
BAE Systems 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 world's first commercial jet airliner; 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, pioneer of the triple-expansion engine and 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 Systems 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 and is a constituent of the FTSE 100 Index.