The use of UAVs by the CIA happened as a result of the 11 September terrorist attacks, in which 2,996 people died, and remains classified top secret.
The CIA's UAV program was commissioned as a result of the 11 September terrorist attacks and the increasing emphasis on operations for intelligence gathering in 2004. 2,996
(2,977 victims + 19 Al-Qaeda terrorists) The CIA's program is covert and remains classified top secret even though it has been widely discussed in the public domain for years. 
