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An unmanned aerial vehicle (UAV) is an aircraft with no onboard pilot. UAVs can be remote controlled aircraft (e.g. flown by a pilot at a ground control station) or can fly autonomously based on pre-programmed flight plans or more complex dynamic automation systems. UAVs are currently used for a number of missions, including reconnaissance and attack roles. For the purposes of this article, and to distinguish UAVs from missiles, a UAV is defined as being capable of controlled, sustained level flight and powered by a jet or reciprocating engine. 

In addition, a cruise missile can be considered to be a UAV, but is treated separately on the basis that the vehicle is the weapon. The acronym UAV has been expanded in some cases to UAVS (Unmanned Aircraft Vehicle System). The FAA has adopted the acronym UAS (Unmanned Aircraft System) to reflect the fact that these complex systems include ground stations and other elements besides the actual air vehicles.


The earliest such aircraft, the Hewitt-Sperry Automatic Airplane was developed during and after World War I, and a number of advances were made with the technology rush that accompanied the Second World War; these were used both to train anti-aircraft gunners and to fly attack missions. Nevertheless, they were little more than full-sized remote controlled airplanes until the Vietnam era. Lately, with the maturing and miniaturization of applicable technologies, interest in such craft has grown within the higher echelons of the US military, as they offer the possibility of cheaper, more capable fighting machines that can be used without risk to aircrews.

Initial generations have primarily been surveillance aircraft, but some have already been fitted with weaponry (such as the MQ-1 Predator, which utilizes AGM-114 Hellfire air-to-ground missiles). The military envisions that more and more roles will be performed by unmanned aircraft, initially bombing and ground attack, with air-to-air combat expected to be the last domain of the fighter pilot for now. A weaponized UAV is known as an Unmanned Combat Air Vehicle, or UCAV for short.

UAVs typically fall into one of five categories (although multi-role airframe platforms are becoming more prevalent):

  • Target and decoy - providing ground and aerial gunnery a target that simulates an enemy aircraft or missile
  • Reconnaissance - providing battlefield intelligence
  • Combat - providing attack capability for high-risk missions (see Unmanned Combat Air Vehicle)
  • Research and development - used to further develop UAV technologies to be integrated into field deployed UAV aircraft
  • Civil and Commercial UAVs - UAVs specifically designed for civil and commercial applications.


The modern concept of UAVs is to have the various aircraft systems work together in a coordinated effort to support the warfighters on the ground. The integration scheme is described in terms of a "Tier" system, and is used by military planners to designate the various individual aircraft elements in an overall usage plan for integrated operations. The Tiers do not refer to specific models of aircraft, but rather roles for which various models and their manufacturers competed. The U.S. Air Force and the U.S. Marine Corps each has its own tier system, and the two systems are themselves not integrated.


  • Tier I: Low altitude, long endurance. Role filled by the Gnat 750.
  • Tier II: Medium altitude, long endurance (MALE). Role currently filled by the MQ-1 Predator and MQ-9 Reaper.
  • Tier II+: High altitude, long endurance conventional UAV (or HALE UAV). Altitude: 60,000 to 65,000 feet, less than 300 knots airspeed, 3,000 nautical mile radius, 24 hour time-on-station capability. Complementary to the Tier III- aircraft. Role currently filled by the RQ-4 Global Hawk.
  • Tier III-: High altitude, long endurance low-observable UAV. Same parameters as, and complementary to, the Tier II+ aircraft. The RQ-3 Dark Star was originally intended to fulfill this role before it was terminated.


  • Tier I: Role currently filled by the Dragon Eye
  • Tier II: Role currently filled by the Scan Eagle and, to some extent, the RQ-2 Pioneer
  • Tier III: Role currently filled by the Pioneer, although USMC planners do not view this aircraft as meeting future Tier III requirements.
Some early UAVs are called drones because they are no more sophisticated than a simple radio controlled aircraft being controlled by a human pilot (sometimes called the operator) at all times. More sophisticated versions may have built-in control and/or guidance systems to perform low level human pilot duties such as speed and flight path stabilization, and simple pre-scripted navigation functions such as waypoint following.
From this perspective, most early UAVs are not autonomous at all. In fact, the field of air vehicle autonomy is a recently emerging field, whose economics is largely driven by the military to develop battle ready technology for the warfighter. Compared to the manufacturing of UAV flight hardware, the market for autonomy technology is fairly immature and undeveloped. Because of this, autonomy has been and may continue to be the bottleneck for future UAV developments, and the overall value and rate of expansion of the future UAV market could be largely driven by advances to be made in the field of autonomy.

Autonomy technology that will become important to future UAV development fall under the following categories:
  • Sensor fusion: Combining information from different sensors for use on board the vehicle
  • Communications: Handling communication and coordination between multiple agents in the presence of incomplete and imperfect information
  • Motion planning (also called Path planning): Determining an optimal path for vehicle to go while meeting certain objectives and constraints, such as obstacles
  • Trajectory Generation: Determining an optimal control maneuver to take to follow a given path or to go from one location to another
  • Task Allocation and Scheduling: Determining the optimal distribution of tasks amongst a group of agents, with time and equipment constraints
  • Cooperative Tactics: Formulating an optimal sequence and spatial distribution of activities between agents in order to maximize chance of success in any given mission scenario

Autonomy is commonly defined as the ability to make decisions without human intervention. To that end, the goal of autonomy is to teach machines to be "smart" and act more like humans. The keen observer may associate this with the development in the field of artificial intelligence made popular in the 1980s and 1990s such as expert systems, neural networks, machine learning, natural language processing, and vision. However, the mode of technological development in the field of autonomy has mostly followed a bottom-up approach, and recent advances have been largely driven by the practitioners in the field of control science, not computer science. Similarly, autonomy has been and probably will continue to be considered an extension of the controls field. In the foreseeable future, however, the two fields will merge to a much greater degree, and practitioners and researchers from both disciplines will work together to spawn rapid technological development in the area.

To some extent, the ultimate goal in the development of autonomy technology is to replace the human pilot. It remains to be seen whether future developments of autonomy technology, the perception of the technology, and most importantly, the political climate surrounding the use of such technology, will limit the development and utility of autonomy for UAV applications.

Under the NATO standardization policy 4586 all NATO UAVs will have to be flown using the Tactical Control System (TCS) a system developed by the software company Raytheon.

Because UAVs are not burdened with the physiological limitations of human pilots, they can be designed for maximized on-station times. The maximum flight duration of unmanned aerial vehicles varies widely. Internal combustion engine aircraft endurance depends strongly on the percentage of fuel burned as a fraction of total weight (the Breguet endurance equation), and so is largely independent of aircraft size. Solar electric UAVs hold the potential for unlimited flight, a concept championed by the Helios Prototype, which unfortunately was destroyed in a 2003 crash.