UAS, or unmanned aircraft system, is the official U.S. Department of Defense term for an unmanned aerial vehicle. Coined by the Navy to reflect the fact that these complex systems include ground stations and other elements besides the actual aircraft, the term was first officially used in the DoD 2005 Unmanned Aircraft System Roadmap 2005–2030. Many people have mistakenly used the term Unmanned Aerial System, or Unmanned Air Vehicle System, as these designations were in provisional use at one time or another.

Military role of unmanned aircraft systems is growing at unprecedented rates. In 2005, tactical- and theater-level unmanned aircraft alone had flown over 100,000 flight hours in support of Operation Enduring Freedom and Operation Iraqi Freedom, in which they are organized under Task Force Liberty in Afghanistan and Task Force ODIN in Iraq. Rapid advances in technology are enabling more and more capability to be placed on smaller airframes which is spurring a large increase in the number of Small Unmanned Aircraft Systems (SUAS) being deployed on the battlefield. The use of SUAS in combat is so new that no formal DoD wide reporting procedures have been established to track SUAS flight hours. As the capabilities grow for all types of UAS, nations continue to subsidize their research and development leading to further advances enabling them to perform a multitude of missions. UAS no longer only perform intelligence, surveillance, and reconnaissance missions. Their roles have expanded to areas including electronic attack, strike missions, suppression and destruction of enemy air defense, network node or communications relay, combat search and rescue, and derivations of these themes.

When the Obama administration announced in December 2009 the deployment of 30,000 new troops in Afghanistan, there was already an increase of attacks by pilot-less Predator drones against Taliban and Al Qaeda militants in Afghanistan and Pakistan's tribal areas, of which one probably killed a key member of Al Qaeda. However, neither Osama bin Laden nor Ayman al-Zawahiri was the likely target, according to reports. According to a report of the New America Foundation, armed drone strikes had dramatically increased under President Obama – even before his deployment decision. There were 43 such attacks between January and October 2009. The report draws on what it deems to be "credible" local and national media stories about the attacks. That compared with a total of 34 in all of 2008, President Bush’s last full year in office. Since 2006, drone-launched missiles allegedly had killed between 750 and 1,000 people in Pakistan, according to the report. Of these, about 20 people were said to be leaders of Al Qaeda, Taliban, and associated groups.