In most instances, military officials convened an accident investigation board to determine the cause. In 18 cases, the drone crashes were so sensitive that the military classified the names of the countries where they occurred and details of what happened.
Two hundred and twenty-four drones crashed in Class B accidents that, under current standards, cost between $500,000 and $2 million. Officials withheld basic details about those mishaps, such as the dates and locations, on the grounds that the lesser damage totals did not warrant a public investigation.
The military documents do not include information about drones operated covertly by the CIA. The spy agency has its own fleet of about 30 armed Predator and Reaper drones overseas, all flown remotely by Air Force pilots assigned to the CIA.
The CIA also flies highly advanced RQ-170 Sentinel surveillance drones, including one that U.S. officials have acknowledged went down in Iran in December 2011.