Political pressure was used on the Central Intelligence Agency to make its reports on the Vietnam War less pessimistic and to conform to the view of foreign policy makers, according to a new study released by the CIA itself.
The book, CIA and the Vietnam Policymakers, uses previously secret documents to show how the agency's reports on the worsening situation were toned down to conform with the more upbeat assessments from US diplomats and other so-called "experts".
The study is written by Mr Harold Ford, a retired CIA officer who drafted many of the intelligence estimates on the situation in Vietnam.
Mr Ford writes: "CIA's judgements proved prescient much of the time but found little receptivity. At other times during 196268, the agency's intelligence found favour with policy makers but turned out to be wrong."
In 1963 a draft National Intelligence Estimate predicted: "The struggle in South Vietnam at best will be protracted and costly [because] very great weaknesses remain and will be difficult to surmount."
But after senior policy makers and military officers objected to this gloomy outlook and after the CIA Director, Mr John McCone, demanded a new draft, the final version read: "We believe that Communist progress has been blunted and the situation is improving."
Mr Ford says that this bowing to "the pressure" by the Director of the CIA and others had lasting consequences. This episode, he writes, "should have provided a valuable lesson in some of the many ways intelligence can be distorted."
"Distortions of reality, some wishful, some more deliberate, persisted until the expulsion of the American presence in Vietnam 12 years later and definitely contributed to that outcome."
Mr McCone himself changed his views on Vietnam two years later when President Lyndon Baines Johnson was preparing to escalate the US military presence and begin a massive bombing campaign.
"We will find ourselves mired down in combat in the jungle in a military effort that we cannot win, and from which we will have extreme difficulty extricating ourselves," Mr McCone wrote in a memo he personally gave to President Johnson in April 1965.
But by that time, Mr Ford writes, Mr McCone and the president had begun to "part company . . . on issues concerning the war."
Reuters adds: CIA working-level officers, unlike Mr McCone, consistently argued in 1963-65 against the consensus view in Washington that South Vietnam could be rescued only by committing US combat forces in the South and systematically bombing North Vietnam, Mr Ford writes.
Instead, lower-level CIA officers held that the war was a political-military struggle that had to be won mainly by the South Vietnamese.
A few CIA officers championed accurate findings that enemy strength in the South was as much as twice as large as the military would acknowledge, Mr Ford reported. But the most senior officers downplayed these warnings, "and so left administration officials unprepared for the shattering of their illusions of progress" after the 1968 Tet offensive, he wrote.