In the $600 billion annual Defense Department budgets, the $22 million spent on the Advanced Aerospace Threat Identification Program was almost impossible to find. Which was how the Pentagon wanted it. For years, the program investigated reports of unidentified flying objects. It was run by a military intelligence official, Luis Elizondo, on the fifth floor of the Pentagon's C Ring. The Defense Department has never before acknowledged the existence of the program, which it says it shut down in 2012. But its backers say that, while the Pentagon ended funding for the effort at that time, the program remains in existence. The shadowy program ... was largely funded at the request of Harry Reid, the Nevada Democrat who ... has long had an interest in space phenomena. Most of the money went to an aerospace research company run by a billionaire entrepreneur ... Robert Bigelow. The program produced documents that describe sightings of aircraft that seemed to move at very high velocities with no visible signs of propulsion, or that hovered with no apparent means of lift. Officials with the program have also studied videos of encounters between unknown objects and American military aircraft. Two other former senators and top members of a defense spending subcommittee - Ted Stevens, an Alaska Republican, and Daniel K. Inouye, a Hawaii Democrat - also supported the program. None of the three senators wanted a public debate ... about the funding for the program, Mr. Reid said. This was so-called black money," he said.