Businesses in the defence sector supply equipment, technology and services used by the armed forces and other government organisations. Their work can cover land, sea and air systems, including vehicles, ships, aircraft, communications equipment, sensors, protective clothing and specialist components. Some firms design and manufacture complete systems, while others provide parts, software, research or engineering expertise. Customers may also use defence businesses for equipment maintenance, upgrades, testing, technical documentation and lifecycle support. Other services can include cyber security, intelligence analysis, logistics, training, simulation and facilities management. Many suppliers work as contractors or subcontractors on projects that involve security, safety and strict technical requirements. The category may include both specialist defence companies and businesses whose wider work includes supplying products or services for military use.