Northrop Grumman defends its high place in the defense sector. As one of the world's top military contractors (behind Lockheed Martin and Boeing), the company operates through four business sectors: Aerospace Systems (aircraft, spacecraft, laser systems, electronic subsystems); Electronic Systems (radar, sensors, chemical detection, countermeasure systems); Information Systems (C4ISR, or command, control, communications, computers, intelligence, surveillance, reconnaissance); and Technical Services (systems support, training and simulation). The US government represents most of Northrop Grumman's sales.