According to MW Cooper, DELTA, or DELTA FORCE, is the designation for the specific arm of the NRO which is especially trained and tasked with security of UFO related projects. Most sources agree that Delta force, e.g. is the unit that provides security at Area 51 and other high security complexes.
Information that was leaked from the Pentagon and published on the Serpo site (www.serpo.org) in August 2006 claims there is a PROJECT DELTA. It allegedly is a highly classified project to develop methods to extract specific material from alien spacecraft. This project is attempting to take materials from known alien artefacts and determine the exact make up of these materials. It would have been launched, or rather first tested, in 2002.
Note that 'Delta Force' also is the popular name for the 1st Special Forces Operational Detachment-Delta, which is one of the United States' counter-terrorism and Special Mission Units. Created in 1977 by Colonel Charles "Charlie" Beckwith, Delta Force is headquartered at Fort Bragg, North Carolina. Its primary tasks are counter-terrorism, direct action, and national intervention operations, although it is an extremely versatile group capable of conducting many types of covert missions, including, but not limited to, hostage rescues and raids.