The Pentagon Papers, a US government report into the Vietnam War, were finally published in full Monday, 40 years after embarrassing details of the document were leaked.
President Lyndon Johnson's administration commissioned a Vietnam Study Task Force in 1967 to write a comprehensive report about America's ill-fated involvement in the Vietnam conflict.
Excerpts were leaked to the New York Times in 1971, showing that successive US administrations had lied to the public about Vietnam, and triggering then president Richard Nixon to attempt to prevent any further such leaks.
Although it is unclear if any new information is contained in the 47-volume report -- much of it has already been published -- Timothy Naftali, head of the Nixon library and museum, welcomed its declassification.
"The point here is that it was intended to be a unified collection. There's a coherence and integrity to the collection which it hasn't had until now. It came out in bits and pieces," he told AFP.
"I can't say why it took so long, but I'm delighted that it has happened," added Naftali, speaking from the Nixon center in the late ex-president's home town of Yorba Linda, east of Los Angeles.
The Pentagon Papers leaks led Nixon to set up a covert White House investigations unit, known as The Plumbers, to prevent further leaks to the media.
Members of it were subsequently implicated in the 1972 burglary at the Watergate complex in Washington DC -- sparking the Watergate scandal which eventually forced the president derisively nicknamed "Tricky Dick" to quit in 1974.
The California Nixon center has long had a copy of the Pentagon Papers -- stamped "Top Secret" -- in its vaults, as have a number of other presidential libraries and the National Archives in Washington DC.
Several of the volumes were put on display in Yorba Linda on Monday, but scholars can study its more than 7,000 pages most easily online, where it is available for the general public to read.