The U.S. government spent quite a bit of money and time investigating UFO reports from the 1940s through the 1990s, and they're finally okay with admitting this. Recently the CIA decided to embrace this history and pointedly opened their declassified investigation files to the public with a blog post offering a "peek into our 'X-Files.'"
The fascinating collection of files is huge, so the CIA decided to peg their reveal to the revival of the X-Files with a list of documents organized by which X-Files lead character would find them the most interesting:
Top 5 CIA Documents Mulder Would Love To Get His Hands On:
1. Flying Saucers Reported Over East Germany, 1952 (PDF 325 KB)
2. Minutes of Branch Chief’s Meeting on UFOs, 11 August 1952 (PDF 162 KB)
3. Flying Saucers Reported Over Spain and North Africa, 1952 (PDF 266 KB)
4. Survey of Flying Saucer Reports, 1 August 1952(PDF 175 KB)
5. Flying Saucers Reported Over Belgian Congo Uranium Mines, 1952 (PDF 262 KB)
Top 5 CIA Documents Scully Would Love To Get Her Hands On:
1. Scientific Advisory Panel on Unidentified Flying Objects, 14-17 January 1953 (PDF 907 KB)
2. Office Memorandum on Flying Saucers, 15 March 1949 (PDF 110 KB)
3. Memorandum to the CIA Director on Flying Saucers, 2 October 1952 (PDF 443 KB)
4. Meeting of the OSI Advisory Group on UFOs, 21 January 1953 (PDF 194 KB)
5. Memorandum for the Record on Flying Saucers, 3 December 1952 (PDF 179 KB)
The accounts found when you click the links are pretty well split along the Mulder and Scully believer/skeptic divide.
On the Mulder side, there is this 1952 report from the Belgian Congo. It tells of "fiery disks" seen "over the uranium mines" which moved in "a precise and light manner, both vertically and horizontally." The report is written in a straighforward manner and sourced to a Congolese officer named Pierre who is considered "dependable" and "a zealous flyer." Given the location of the sighting, it's hard to not pause for a moment and consider it was 1952, the nuclear era was still young, and uranium mines were a focus of interest for the emerging nuclear nations. It would make sense that someone was paying them undue attention.
The skeptic sympathetic to the clear-eyed Agent Scully worldview will appreciate the tone of this 1949 memo from the OSI's (the original name of the CIA) Dr. Machle to a Dr. Stone. The author of the memo admits documents regarding UFO sightings—which had become quite common in the years just after World War II—are confusing and just make him want to lie down. He goes on to criticize not considering weather balloons as possible sources of sighting reports. He also points out that sightings peaked in July—when both fireworks and in some parts of the country thunder and lightning often fill the sky.
No matter what you think about the possibility of extraterrestrial visitations, the files make for absorbing reading. They give a fascinating look at a time when the Central Intelligence Agency had no choice but to take seriously and investigate reports that today seem mostly consigned to feverish discussions on late-night radio and on Internet forums.
Who knows, maybe the CIA is investigating such things even today—they just don't want us to know about it. The truth, whatever it may be, is still out there, somewhere.