CIA documents reveal spy plane testing at Area 51

"High-altitude testing of the U-2 soon led to an unexpected side effect -- a tremendous increase in reports of unidentified flying objects (UFOs)," the report states, saying that more than a half of UFO reports during the 1950s and 1960s could be attributed directly to military test flights.

The report also details some of the extreme steps the government took to maintain secrecy at the facility.

"As the deliveries of U-2 airframes to the testing site increased, a major logistic problem arose: how to transfer Lockheed employees from Burbank [Calif.] to Area 51 without arousing a great deal of curiosity," the documents say.

"The project staff decided that the simplest approach would be to fly the essential personnel to the site on Monday morning and return them to Burbank on Friday evening."

The request for information about the compound was submitted in 2005 by Jeffrey T. Richelson, a senior fellow at the National Security Archives.

The researcher told the Las Vegas Sun that the release "marks an end of official secrecy about the facts of Area 51."

"It opens up the possibility that future accounts of this and other aerial projects will be less redacted, more fully explained in terms of their presence in Area 51," he said.