Since 1917, United States military services have researched and employed unmanned aerial vehicles (UAVs). Over that time, they have been called drones, robot planes, pilotless aircraft, RPVs (remotely piloted vehicles), RPAs (remotely piloted aircraft) and other terms describing aircraft that fly under control with no person aboard. They are most often called UAVs, and when combined with ground control stations and data links, form UAS, or unmanned aerial systems. The Department of Defense (DOD) defines UAVs as powered, aerial vehicles that do not carry a human operator, use aerodynamic forces to provide vehicle lift, can fly autonomously or be piloted remotely, can be expendable or recoverable, and can carry a lethal or nonlethal payload. Ballistic or semi-ballistic vehicles, cruise missiles, and artillery projectiles are not considered UAVs by the DOD definition. UAVs are either described as a single air vehicle (with associated surveillance sensors), or a UAV system (UAS), which usually consists of three to six air vehicles, a ground control station, and support equipment. Although only recently procured in significant numbers by the United States, UAS were first tested during World War I, although not used in combat by the United States during that war. Indeed, it was not until the Vietnam War that the United States employed UAS such as the AQM-34 Firebee in a combat role. The Firebee exemplifies the versatility of UAS—initially flown in the 1950s as an aerial gunnery target and then in the 1960s as an intelligence-collection drone, it was modified to deliver payloads and flew its first flight test as an armed UAV in 2002. The military use of UAS in conflicts such as Kosovo (1999), Iraq (since 2003), and Afghanistan (since 2001) has illustrated the advantages and disadvantages of unmanned aircraft. UAS regularly make national headlines as they perform tasks historically performed by manned aircraft. UAS are thought to offer two main advantages over manned aircraft: they eliminate the risk to a pilot's life, and their aeronautical capabilities, such as endurance, are not bound by human limitations. UAS also protect the lives of pilots by performing those dull, dirty, or dangerous missions that do not require a pilot in the cockpit. UAS may also be cheaper to procure and operate than manned aircraft. However, the lower procurement cost of UAS can be weighed against their greater proclivity to crash, while the minimized risk to onboard crew can be weighed against the complications and hazards inherent in flying unmanned vehicles in airspace shared with manned assets. UAS use has increased for a number of reasons. Advanced navigation and communications technologies were not available just a few years ago, and increases in military communications satellite bandwidth have made remote operation of UAS more practical. The nature of the Iraq and Afghanistan wars has also increased the demand for UAS, as identification of and strikes against targets hiding among civilian populations required persistent surveillance and prompt strike capability, to minimize collateral damage. Further, UAS provide an asymmetrical—and comparatively invulnerable—technical advantage in these conflicts. For many years, the Israeli Air Force led the world in developing UAS and tactics. U.S. observers noticed Israel's successful use of UAS during operations in Lebanon in 1982, encouraging then-Navy Secretary John Lehman to acquire a UAS capability for the Navy. Interest also grew in other parts of the Pentagon, and the Reagan Administration's FY1987 budget requested notably higher levels of UAS funding. This marked the transition of UAS in the United States from experimental projects to acquisition programs. Initial U.S. capabilities came from platforms acquired from Israel. One such UAS, Pioneer, emerged as a useful source of intelligence at the tactical level during Operation Desert Storm, when Pioneer was used by Navy battleships to locate Iraqi targets for its 16-inch guns. Gulf War experience demonstrated the potential value of UAS, and the Air Force's Predator was placed on a fast track, quickly adding new capabilities. Debuting in the Balkans conflict, the Predator performed surveillance missions such as monitoring area roads for weapons movements and conducting battle damage assessment. Operations in Iraq and Afghanistan have featured the Air Force's Global Hawk, as well as adding a new mission that allows the Predator to live up to its name—armed reconnaissance. Reflecting a growing awareness and support for UAS, Congress has increased investment in unmanned aerial vehicles annually. The FY2001 investment in UAS was approximately $667 million. For FY2012, DOD has asked for $3.9 billion in procurement and development funding with much more planned for the outyears. DOD's inventory of unmanned aircraft increased from 167 to nearly 7,500 from 2002 to 2010. DOD's UAS research and development (R&D) funding has also grown, for a variety of reasons: UAS are considered a growth industry, many UAS are relatively inexpensive to produce, and new technology in miniaturization has helped accelerate the development of many UAS types. Congress has approached UAS development with strong encouragement tempered with concern. Notably, in 2000, Congress set the goal of making "one-third of the aircraft in the operational deep strike force aircraft fleet" unmanned. Congress has also directed the formation of joint program offices to ensure commonality among the services' UAS programs. Following expressed concern that DOD's "growing enthusiasm may well lead to a situation in which there is no clear path toward the future of UAS," Congress also required DOD to submit a UAS roadmap. In some instances, Congress has chastened DOD for what it saw as a leisurely rate of UAS acquisition and encouraged it to speed up this pace, or speed up the incorporation of certain capabilities. For example, in 1996, the House Armed Services Committee (HASC) supported legislation directing DOD to weaponize both the Predator and Hunter, but DOD opposed the initiative. Although this report focuses on the military uses of UAS, Congress's interest in UAS extends beyond the defense committees, as UAS capabilities have also led to their use in missions outside the military. The Department of Homeland Security operates UAS to help patrol U.S. borders, and Congress has questioned the efficacy of such operations. Further, the use of UAS in a variety of roles, but particularly as platforms for delivering lethal force, raises a number of legal issues of interest to Congress. In today's military, unmanned systems are highly desired by combatant commanders for their versatility and persistence. By performing tasks such as surveillance; signals intelligence (SIGINT); precision target designation; mine detection; and chemical, biological, radiological, nuclear (CBRN) reconnaissance, unmanned systems have made key contributions to the Global War on Terror. To be sure, manned systems could accomplish many if not all of the same goals. But "unmanned systems reduce the risk to our warfighters by providing a sophisticated stand-off capability that supports intelligence, command and control, targeting, and weapons delivery. These systems also improve situational awareness and reduce many of the emotional hazards inherent in air and ground combat, thus decreasing the likelihood of causing civilian noncombatant casualties." "UAVs have gained favor as ways to reduce risk to combat troops, the cost of hardware and the reaction time in a surgical strike" and "to conduct missions in areas that are difficult to access or otherwise considered too high-risk for manned aircraft or personnel on the ground." As a result, "The number of platforms in this category—R/MQ-4 Global Hawk-class, MQ-9 Reaper, and MQ-1 Predator-class unmanned aircraft systems (UAS)—will grow from approximately 340 in FY 2012 to approximately 650 in FY 2021." Some in the military also tout UAS's reduced cost of acquisition and operation when compared to manned platforms. However, the Congressional Budget Office cautions that savings cannot be taken for granted: Unmanned aircraft systems are usually less expensive than manned aircraft. Initial concepts envisioned very low-cost, essentially expendable aircraft. As of 2011, however, whether substantially lower costs will be realized is unclear. Although a pilot may not be on board, the advanced sensors carried by unmanned aircraft systems are very expensive and cannot be viewed as expendable.... Moreover, excessively high losses of aircraft can negate cost advantages by requiring the services to purchase large numbers of replacement aircraft. Intelligence gathering is UAS' traditional mission. In the 1960s, autonomous drones were used for reconnaissance in the Vietnam War and on strategic reconnaissance missions over denied areas. Early modern controllable UAS were used to loft cameras to allow units in the field to observe opposing forces beyond direct line of sight. Subsequently, longer-endurance systems introduced the ability to maintain surveillance on distant and moving targets. The first UAS were essentially unpiloted bombs, designed to fly in a particular direction until the fuel ran out, at which point the entire aircraft would plunge to the ground. Today, some UAS carry precision-guided weapons to attack ground targets, and more are being weaponized, although this is still adding strike capability to systems originally designed for reconnaissance. A separate class of UAS is being designed from the ground up to carry out combat missions. Called unmanned combat air vehicles, or UCAVs, these systems feature greater payload, speed, and stealth than current UAS. The Navy is investigating how UAS could deliver cargo to ships at sea, and the Marine Corps has awarded contracts to two firms to demonstrate how UAS might resupply units in Afghanistan. Early research is underway to develop the capability for an unmanned system to locate and possibly evacuate personnel behind enemy lines.