But key questions -- including how targets are chosen and an official civilian death count -- remain unanswered.
At least 2,400 people have been killed by U.S. drone strikes since President Obama took office five years ago this week.
More than a tenth of the deaths -- at least 273 -- belong not to suspected terrorists, but civilians, according to data tracked by The Bureau of Investigative Journalism. More than 390 drone strikes, in total, have been used against Pakistan, Yemen, and Somalia.
The administration's use of drone strikes has become a familiar, nearly constant point of contention with some allies in the Middle East, particularly Pakistan. A key supply route between Afghanistan and Pakistan continues to be blocked off as Pakistanis protest the U.S.'s use of drones. The country's prime minister told Defense Secretary Chuck Hagel last month that its "counter-productive" to U.S.-Pakistani counterterrorism measures.
If the Torkham border crossing isn't reopened, the Defense Department could be forced to pay up to $1 billion more to move military equipment out of Afghanistan.
But the administration has scaled back its use of drones in recent years. Pakistan was the target of 28 drones strikes in 2013, down from a high of 117 in 2010, according to the Long War Journal. The president launched his first strike against Pakistan on Jan. 23, 2009 -- his third day in office.
And though the administration has struck Yemen three times so far this year, drone strikes were down in 2013 at 26, from a 2012 high of 41.
There is some discrepancy on the total number of U.S. strikes and how many people have been killed by them. Almost 2,700 people have been killed by drone strikes in Yemen and Pakistan since 2009, according to the Long War Journal, with 205 of those deaths belonging to civilians. The organization doesn't track annual drone strikes in Somalia -- where the Obama administration has targeted al-Shabaab militants.
The imprecision on exactly how many drones strikes the United States has used, or how many people have been killed, underscores the lack of transparency surrounding the U.S. drone campaign.
And though the president pledged last year to be more transparent about his administration's use of drones, as ProPublica notes key questions still remain including how many civilians the administration believes it has killed, how it makes it targets, or the specific legal reasoning it uses for the strikes.
And a move to transfer oversight of the U.S. drone program from the CIA to the Pentagon was recently blocked by Congress under the omnibus bill. Such a move could have shed more light on some of the missing holes in the public's knowledge of drones, but members of Congress have voiced hesitation on the Defense Department's ability to effectively and accurately manage the program.
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