Unmanned aerial vehicles (UAVs), otherwise known as drones, are remotely-controlled aircraft which may be armed with missiles and bombs for attack missions. Since the World Trade Center attacks of Sep. 11, 2001 and the subsequent "War on Terror," the United States has used thousands of drones to kill suspected terrorists in Pakistan, Afghanistan, Yemen, Somalia, and other countries.
Proponents say that drones have decimated terrorist networks abroad via precise strikes with minimal civilian casualties. They contend that drones are relatively inexpensive weapons, are used under proper government oversight, and that their use helps prevent "boots on the ground" combat and makes America safer.
Opponents say that drone strikes create more terrorists than they kill. They contend that drone strikes kill large numbers of civilians, violate international law, lack sufficient congressional oversight, violate the sovereignty of other nations, and make the horrors of war appear as innocuous as a video game.
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The "Intrepid," a hydrogen gas balloon built for use by the Union Army Balloon Corps for aerial reconnaissance and guiding artillery fire during the American Civil War. Source: Library of Congress, "Prof. Thaddeus S. Lowe Replenishing Balloon INTREPID from Balloon CONSTITUTION," loc.gov, May 1862
The first recorded use of attack drones occurred on July 15, 1849 when the Habsburg Austrian Empire launched 200 pilotless balloons armed with bombs against the revolution-minded citizens of Venice.  Reconnaissance balloons were flown in the US Civil War by Union and Confederate forces in order to provide intelligence information ahead of a battle and to direct ground artillery fire during battle.  In 1944 Japan released 9,000 bomb-laden balloons across the Pacific, intending to cause forest fires and panic in the western United States. 
The modern electronically-controlled military drone traces its origins to the 1930s when the British Royal Navy developed the Queen Bee, a radio-controlled drone used for aerial target practice by British pilots.  Technology developed by the US Navy during World War I was used to propel and stabilize drones on intelligence-gathering missions in Europe during World War II and over Vietnam, China, and North Korea during the Vietnam War. 
What Is a Drone?
Today, companies have developed dozens of drone models ranging in size from large, solar-powered, fixed-wing aircraft to small helicopter-like devices designed to mimic hummingbirds, all with a wide range of prices and capabilities.  The two most widely-used attack drones are the MQ-1 Predator (which the US military ceased purchasing in Feb. 2011) and the upgraded MQ-9 Reaper, both developed by military contractor General Atomics Aeronautical Systems.  The Predator and Reaper are prized for their ability to hover thousands of feet above a target for hours and relay high-resolution live surveillance.  The Predator was first deployed by NATO convoys as a surveillance and intelligence gathering tool for spotting Serbian artillery during the Bosnian war in 1995, while the Reaper was first deployed in 2007 during the Iraq and Afghanistan wars. 
The Reaper is powered by a 900 horsepower turboprop engine with a maximum speed of about 276 miles per hour. It has a wingspan of 66 feet, is 36 feet long, 12.5 feet high, carries a maximum payload of 3,850 pounds, and can be armed with a variety of weaponry, including up to 14 missiles or a combination of four missiles and two laser-guided bombs.  This drone has a range of 3,682 miles, an operational altitude of 50,000 ft, and a maximum flight time of 27 hours, making it especially useful for long-term operations.  The Reaper carries approximately 15 times the amount of ordnance payload of the Predator, and cruises at nearly three times the speed. 
CIA and JSOC Drone Operation
Drones used for strike operations abroad are flown by both civilians – intelligence officers and private contractors – in the Central Intelligence Agency (CIA) and experienced Air Force pilots under the military's Joint Special Operations Command (JSOC).  The CIA operates on its own in Pakistan, where approximately 80% of US drone strikes have been carried out.  JSOC currently has responsibility for drones in Afghanistan and Somalia, and co-responsibility with the CIA for drones in Yemen. 
One set of operators works abroad handling takeoffs and landings near hidden airfields in countries such as Afghanistan, Pakistan, Niger, Ethiopia, Qatar, Saudi Arabia, United Arab Emirates, and Djibouti.  Once the drones are aloft, controls are electronically "slewed over" to a set of "reachback operators" in the United States. Using joysticks that resemble video-game controls, the reachback operators sit next to intelligence officers and watch a live video feed from the drone’s camera on large flat-screen monitors. They can turn the drone, zoom in on the landscape below, and decide whether to lock onto a target.
A stream of additional "signal intelligence," sent by the National Security Agency, provides electronic means of corroborating that a target has been correctly identified. Final approval for strikes with missiles or laser-guided bombs is delegated to CIA and JSOC officials.  Drone pilots are eligible for the same combat-related medals from the Department of Defense as manned aircraft pilots. 
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Ground-based cockpit for manning the controls of a Reaper drone. Source: Defense Department via the Associated Press, "Flashy Drone Strikes Raise Status of Remote Pilots," bostonglobe.com, Aug. 12, 2012
By 2015, the Pentagon projects that JSOC will need more than 2,000 drone pilots for combat air patrols operating 24 hours a day worldwide.  The Air Force is already training more drone pilots – 350 in 2012 – than fighter and bomber pilots combined. 
Cost of Drones
The Pentagon operates some 7,000 drones while the CIA operates around 30,  and each drone costs anywhere from $5 million for a Predator to $14.4 million for a Reaper.  The Department of Defense's fiscal year 2012 budget estimates included nearly $5 billion for drone research, development,  and procurement (around 1% of the overall DoD budget),  with additional funding that is classified.
The cost per flight hour varies by type of drone, but Predator and Reaper drones cost approximately $3,700 to $4,800 per flight hour.  The entire US drone program took 14 years to reach one million flight hours on June 22, 2011,  and on Oct. 22, 2013, less than two and a half years later, the Air Force's fleets of Predators and Reapers reached two million flight hours. 
The Unmanned Systems Caucus, co-chaired by Congressman Howard P. "Buck" McKeon (R-CA) and Henry Cuellar (D-TX), promotes the use of drone technologies in the US House of Representatives. The 58-member caucus includes eight Congressmen who also sit on the House Committee on Appropriations, and from 2011 to 2012 members received a total of $2.3 million in contributions from political action committees affiliated with drone manufacturers. 
The War on Terror, High Value Targets, and Signature Strikes
On Sep. 7, 2000, the CIA lobbied for Predator drones to be weaponized with air-to-ground missiles for future use as a battlefield weapon after spotting Osama bin Laden in Afghanistan, who was then wanted for his role in financing and organizing terrorist attacks against American embassies in Tanzania and Kenya in 1998. 
After the World Trade Center was attacked on Sep. 11, 2001, the Bush administration immediately authorized the armed Predator program and the first drones arrived in Afghanistan on Oct. 7, 2001.  President Bush signed a Memorandum of Notification creating a secret list of "High Value Targets" that the CIA was authorized to kill anywhere in the world without further presidential approval.  The administration’s first known Predator strike occurred on Feb. 4, 2002 in Afghanistan, when a CIA Predator drone fired on a group they believed included Osama bin Laden.  The targets, all killed, were civilians gathering scrap metal.  The first known successful targeted killing occurred outside of a declared war zone, killing suspected USS Cole bombing mastermind Qaed Salim Sinan al-Harethi in Yemen on Nov. 4, 2002. 
Since 9/11, over 95% of all non-battlefield targeted killings have been conducted by drones.  The CIA under the Bush Administration mostly engaged in "personality" strikes targeting known terrorists whose identities had been firmly established through intelligence, including visual surveillance and electronic and human intelligence.  In 2008, the CIA began a policy of "signature strikes" against targets outside of named kill lists, targeting individuals based on their "pattern of life" or their suspicious daily behavior.  In Pakistan in 2009 and 2010, as many as half of the 170 strikes were classified as signature strikes. Obama ordered around 280 drone strikes in Pakistan in his first presidential term alone, nearly seven times as many as in George W. Bush's second term. 
The United States operates drones with the tacit consent of the leaders of Pakistan, Yemen, Somalia, and Afghanistan.  The parliaments and governing bodies of these countries, however, often issue public statements blasting the attacks,  and public sentiment is strongly anti-drone. 
Number of Strikes and Casualties
Different sources – both private and governmental – report different numbers for the number of strikes and combatant and civilian deaths. According to counts from the New America Foundation, Long War Journal, and The Bureau of Investigative Journalism, around 3,500 militants in Pakistan, Afghanistan, Yemen, and Somalia have died in drone attacks.  A meta-study of drone strikes concluded 8 to 17% of all people killed in drone strikes are civilians. 
Since 2002, the United States has conducted a covert program to target and kill al Qaeda members based in Yemen. The first and only US drone strike of the Bush Administration in Yemen launched in 2002, and the strikes resumed in 2009 during President Barack Obama’s first term after a seven year hiatus. Between 2002 and Dec. 12, 2013, an estimated 57-82 drone strikes in Yemen resulted in the deaths of 268 to 790 "enemy," "extremist," or "militant" deaths, as well as 27-84 civilian deaths. 2012 was considered the deadliest year (approximately 42 airstrikes and 238 casualties). In 2013, the number of strikes and civilian deaths fell to 25 and 114 respectively following public awareness and outcry over the attacks. 
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The number of US drone strikes in Pakistan from 2004 - 2013. Source: Bill Roggio and Alexander Mayer, "Charting the Data for US Airstrikes in Pakistan, 2004 - 2013," longwarjournal.org, Nov. 29, 2013
Since 2004, the United States has conducted a covert program to target and kill al Qaeda and Taliban commanders based in Pakistan's northwest tribal regions. 96% of these strikes have taken place in the two regions of North and South Waziristan on the border with Afghanistan. Between 2004 and Nov. 29, 2013, an estimated 326-380 drone strikes in Pakistan resulted in 1,620-2,783 "enemy," "extremist," or "militant" deaths, as well as 156-951 civilian deaths. Pakistan told the United Nations in Oct. 2013 that at least 400 civilians have died from the attacks. 2010 was the deadliest year in Pakistan in both number of strikes and deaths. Both have declined sharply since. 
The United States has conducted three to nine drone strikes against al Shabaab Islamic militants in Somalia between 2007 and Oct. 31, 2013, resulting in seven to 27 deaths, up to 16 of whom were civilians. 
Public Outcry and Reform
In a Freedom of Information Act request filed on Jan. 13, 2010, the American Civil Liberties Union (ACLU) asked the government to disclose the legal and factual basis for its use of drones to conduct targeted killings abroad.  In particular, they sought to find out when, where, and against whom drone strikes can be authorized, and how the United States ensures compliance with international laws relating to extrajudicial killings.  A federal appeals court judge ruled on Mar. 15, 2013 that the CIA can no longer assert the "fiction" that it can’t reveal if it has a drone program,  but the CIA has refused to release information for "national security" purposes. 
In Sep. 2011, President Obama authorized the targeted killing of Anwar al-Awlaki, an American citizen tied to terrorist attacks.  The Awlaki strike also killed another American, Samir Khan, who officials say was not intentionally targeted. A subsequent strike killed Mr. Awlaki’s 16-year-old American son, a death that officials say was an accident. A leaked white paper from the Department of Justice outlining the legal rationale for killing Americans affiliated with terrorist groups abroad claimed that an "individual’s [American] citizenship would not immunize him from a lethal operation." 
Obama officially acknowledged drone strikes in Pakistan for the first time in a Jan. 2012 Google+ Hangout.  He openly referenced drone strikes in Yemen and Somalia for the first time in a June 2012 letter to Congress. 
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Protesters burn an effigy of a US drone in Sanaa, Yemen on Apr. 12, 2013. Source: Khaled Abdullah, "US Drone Strikes Leave Yemenis Frustrated, Hopeless," al-monitor.com, Sep. 30, 2013
Under the stewardship of John O. Brennan, the president’s counter-terrorism adviser from Jan. 20, 2009 to Mar. 8, 2013, officials spent months discussing how to be more transparent about a program that was still officially secret and how to define its limits.  Members of the Senate Intelligence Committee questioned Brennan on the use of drones for targeted killing during his confirmation hearing to become head of the CIA on Feb. 7, 2013, acknowledging "widespread debate" about the program.  On Apr. 23, 2013, the Senate Judiciary Committee held a hearing on drone strikes, and heard from a range of witnesses on the constitutional and counter-terrorism implications of targeted killings. 
On May 23, 2013, President Obama made a speech at National Defense University outlining his justification for the drone program and promising more transparency and tighter policies toward targeted killings.  Obama stated in the speech that the United States would only take military action against a "continuing and imminent threat to the American people." The day before the speech, Obama issued "Presidential Policy Guidance" establishing five criteria that must be met before lethal action may be taken against a foreign target: "1) Near certainty that the terrorist target is present; 2) Near certainty that non-combatants will not be injured or killed; 3) An assessment that capture is not feasible at the time of the operation; 4) An assessment that the relevant governmental authorities in the country where action is contemplated cannot or will not effectively address the threat to U.S. persons; and 5) An assessment that no other reasonable alternatives exist to effectively address the threat to US persons." 
On Apr. 23, 2015, the US government disclosed that two civilian aid workers being held hostage by al Qaeda in Pakistan were killed by a US drone strike back in January 2015. The incident renewed the debate over the CIA's control over the drone program in Pakistan and US drone policy in general. The Obama administration and Senate leaders, including Sen. John McCain (R-AZ), expressed interest in transferring military drone control to the Department of Defense.
On Oct. 15, 2015, a collection of classified documents about the US drone program was released by an anonymous whistleblower and included revelations that as many as 90 percent of US drone killings in a five-month period were not the intended targets; that there is a clear chain of command in determining targets and authorizing strikes; and that unintended deaths from strikes were classified as "enemies killed in action" regardless of whether the casualties were civilians or combatants.