While the French were trying to get out of Vietnam for good, Americans were serving as their advisors. There weren't many at first - perhaps a few hundred. But those advisors, even in the early days of the Kennedy Administration, were unable to defend themselves when they were shot at. And, according to Graham Greene's novel The Quiet American, they conducted covert operations even in the 1950s.
Greene spent some time in Vietnam. Scholars think his character "Thomas Fowler," a crusty reporter for the London Times, is likely based on the author himself. There is little doubt whom Greene used as a model when he invented the American "Alden Pyle." It was Edward Lansdale, about whom Greene frequently made harsh comments. (Lansdale, it is said, returned those "compliments.")
The Quiet American begins as French involvement in Vietnam is ending. Fowler, who cares more about opium than he does the political climate, does not want to get involved. Pyle, a young American with good intentions, does his best to stir things up.
Pyle is a nominal pharmaceuticals distributor, but that's just his cover. His real job is to help create an indigenous South Vietnamese force which can overthrow the growing power of the Viet Minh. He's an American military advisor sent to help the French fight Vietnamese communism. His mission is to teach the French what they need to know about guerilla warfare. His fictional support of a "Third Force" was, in real life, like America's support of Ngo Dinh Diem - the man the U.S. wanted to replace the French-backed emperor, Bao Dai. But Pyle, in the story, ends up burning a village in order to save it. Not unlike, parenthetically, what happened to Diem in 1963.
Using the British experience in Burma as his model, Greene's book (first published in 1955) included uncanny predictions about American involvement in Vietnam. Those observations, spoken by the character of Thomas Fowler, created a furor at the time and since. It was likely, mused Fowler, that the United States, like the United Kingdom, would grow tired of its involvement. If that happened, the Americans - like the Brits - would leave the indigenous people to fight on their own.
And where would that lead, according to Fowler? To slaughter of the natives by their enemy.