Editor's note: This story was initially published in mid-April 2013 and has been updated.
Washington (CNN) -- On the eve of a speech by President Barack Obama about his administration's counterterrorism policy, Attorney General Eric Holder acknowledged for the first time Wednesday that U.S. drone strikes have killed four Americans overseas since 2009.
Here's a look at drones by the numbers:
1917: The year the U.S. military first began researching and using unmanned aerial vehicles (UAV).
1990: The year the Federal Aviation Administration first approved the use of unmanned aircraft in national airspace.
9.31 per 100,000: Combined total of accidents per flying hour of unmanned aerial vehicles in the U.S. Air Force fleet, made by Northrup Grumman Corp. and General Atomics Aeronautical Systems Inc., according to a June 2012 analysis by Bloomberg.
20.4: Percentage of the global UAS (unmanned aerial systems) market held by General Atomics Aeronautical Systems Inc., the largest of any American company.
18.9: Percentage of the global UAS market held by Northrup Grumman Corp., second largest American company.
41: Percentage of the total of Department of Defense aircraft that are unmanned, as of 2010.
355: Total number of known U.S. military drone strikes in Pakistan from 2004 to 2013, according to the New America Foundation.
120: Total number of known U.S. military drone strikes in Yemen between 2002 and 2013, according to the New America Foundation.
5: Members of the class of 2011 at the University of North Dakota who were the first in the United States to receive degrees in unmanned aircraft systems operations.
$26.16 billion: Amount of funding for UAS requested for Fiscal Year 2013 in the president's budget.
$6.6 billion: Worldwide spending on unmanned aerial systems research and development and procurement in 2013, according to research estimates by the Teal Group.
$11.4 billion: Estimated spending on UAS research, development and procurement in 2022.
6: Proposed FAA test sites for unmanned aircraft systems (UAS) research and test sites around the country.
24: States reportedly competing for contracts to build a test site.
327: Drone permits (called "certificates or authorization of waiver") active in the United States as of February 2013.
1014: Permits issued since 2009.
Nearly 13 hours: Sen. Rand Paul's filibuster in March of John Brennan's nomination as CIA director over U.S. drone policy.