The CIA is putting its secret history online, uploading millions of newly declassified documents.

The documents include previously unseen information about the agency's hunt for UFOs and its work on the "Star Gate" project, which tried to teach humans to become psychic and see through walls.

One document, for instance, describes that project in detail. It shows how the CIA recruited volunteers to go through a programme of training that would let people access information without any of the usual means, and which would be used as a weapon for which there is "no known defense".

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The US spy agency will put up 12 million pages into its online "reading room", where people will be able to search through the documents.

The previously classified pages include private briefs given to presidents and the information that is passed between its operatives. They cover everything from the Cold War and Vietnam to relatively modern problems like terrorism.

That means that people can see its history from its formation until the early 90s, for now. None of that is selected, the agency claims, meaning that it shows some of the agency and the US government's most controversial episodes.

The CIA has to declassify records that are 25 years old, unless they are made exempt. That means that each year it releases a whole new set of documents.