Almost everything about the U.S. military's Area 51 flight test facility, also known as Groom Lake, is shrouded in secrecy and mystery. This even extends to the base's small and unique fleet of HH-60U rescue helicopters, sometimes called Ghost Hawks, which at least help provide security, local search and rescue, and other types of utility support in and around the base.
The Air Force is understood to have a total of four HH-60Us, one of which is seen at the top of this story and all of which are modified examples of the U.S. Army's HH-60M Black Hawk medical evacuation (MEDEVAC), or "Dustoff," helicopter. Area 51 watchers have determined that the U models are likely assigned to a unit colloquially know as the "Ghost Squadron." This helicopter unit is one of a number of secretive elements associated with Detachment 3, Air Force Flight Test Center, which appears to be one of the main Air Force entities at Groom Lake. Detachment 3 also reportedly oversees operations involving other more traditional aircraft and so-called "Foreign Materiel Exploitation," or FME, examining non-American aircraft and systems at the secretive base, along with its other top-secret flight test duties.