Washington A 1967 memo on Vietnam, delivered to then-President Johnson in a sealed envelope, eerily foretold what happened in Saigon nearly eight years later.
"There could be a spectacle of panic flight from the country ... and Communist terror and vengeance," said the CIA memo.
The scenario was laid out in one of 174 intelligence documents released by the government Friday, a day before the 30th anniversary of Saigon's fall.
The documents spanning from 1948 to 1975 show where the spy community had it right -- and wrong -- on Vietnam.
"Implications of an unfavorable outcome in Vietnam," the 1967 memo was entitled.
But even that worst-case scenario envisioned a better outcome than what actually occurred. It assumed a negotiated settlement that favored the North, and called a possible political and military collapse an "entirely implausible hypothesis."
The 1967 memo also bluntly stated what some historians have viewed as one of the central lessons of Vietnam that still echoes today: Such a loss would demonstrate the United States "cannot crush a revolutionary movement which is sufficiently large, dedicated, competent, and well-supported."
"In a narrow sense," it added, "this means more simply that the structure of U.S. military power is ill-suited to cope with guerrilla warfare waged by a determined, resourceful, and politically astute opponent."
In an introduction to the compilation of documents, Lloyd Gardner, a Rutgers University history professor, said the intelligence papers laid out the "convictions and doubts of the intelligence community" as they changed over time.
"They are often ahead of the curve and occasionally lag behind the pace of events," said Gardner, a specialist on the Vietnam War.
The documents were released by the National Intelligence Council, the government's leading analysts who coordinate the judgments of the various intelligence agencies and provide them to policy-makers.
They come on the eve of the 30th anniversary of the April 30, 1975, fall of Saigon to communist troops, ending the Vietnam War. All but a small number of Americans were evacuated a few days earlier, along with U.S. Ambassador Graham Martin.
In the collection's final installment, dated March 1975, U.S. intelligence analysts said even if the ongoing North Vietnamese attack were blocked, the South Vietnamese government would find itself in control of very little.
The estimate "foresaw final defeat by early 1976, a prediction still too generous as it turned out," Gardner wrote.