A monitoring aircraft is an aircraft which is used for monitoring. They are operated in roles such as intelligence gathering, battlefield surveillance, airspace surveillance, reconnaissance, observation (e.g. spotting artillery), border patrol, and fishery protection by military forces and other government agencies. This article focuses not on traffic monitoring, law enforcement and similar activities but on aircraft used in those roles. Surveillance aircraft do not usually carry any armaments, or limited defensive weapons. These do not always require high-performance capability or stealth features, and civilian aircraft may be modified as well.