But his extreme attention to technical detail earned him respect inside the intelligence community and beyond and helped make Clancy the most widely read and influential military novelist of his time, one who seemed to capture a shift in the country's mood away from the CIA misdeeds that came out in the 1970s to the heroic feats of Clancy's most famous creation, CIA analyst Jack Ryan.
Several of his novels, including "The Hunt for Red October," "Patriot Games" and "Clear and Present Danger," were later made into blockbuster movies, with another, "Jack Ryan," set for release on Christmas.
"Fundamentally, I think of myself as a storyteller, not a writer," Clancy once said. "I think about the characters I've created, and then I sit down and start typing and see what they will do. There's a lot of subconscious thought that goes on. It amazes me to find out, a few chapters later, why I put someone in a certain place when I did. It's spooky."
A tall, trim figure given to wearing sunglasses that made him look like a fighter pilot, Clancy had such a sure grasp of defense technology and spycraft that many readers were convinced he served in the military. But his experience was limited to ROTC classes in college. Near-sightedness kept him out of active duty.
A political conservative who once referred to Ronald Reagan as "my president," Clancy broke through commercially during a tense period of the Cold War, and with the help of Reagan himself.
In 1982, he began working on "The Hunt for Red October," drawing inspiration from a real-life 1975 mutiny aboard a Soviet missile frigate. He sold the manuscript to the first publisher he tried, the Naval Institute Press, which had never bought original fiction.
In real life, the mutiny was put down, but in Clancy's book, a Soviet submarine skipper hands his vessel over to the U.S. and defects.
Someone thought enough of the novel to give it to Reagan as a Christmas gift. The president quipped at a dinner that he was losing sleep because he couldn't put the book down — a statement Clancy later said helped put him on the New York Times best-seller list.
"What happened to me was pure dumb luck. I'm not the new Hemingway," Clancy later said in an interview with the American Movie Channel.
"Of course, fortune does favor the brave. In battle, you forgive a man anything except an unwillingness to take risks. Sometimes you have to put it on the line. What I did was take time away from how I earned my living. My wife gave me hell. 'Why are you doing this?' But she doesn't complain anymore."
Clancy said his dream had been simply to publish a book, hopefully a good one, so that he would be in the Library of Congress catalog. His dreams were answered many times over.
His novels were dependable hits, his publisher estimating worldwide sales at more than 100 million copies.
Alec Baldwin, Ben Affleck and Harrison Ford were among the actors who played Jack Ryan on screen. The upcoming movie stars Chris Pine, with Kenneth Branagh directing. Keira Knightly plays his wife and Kevin Costner his mentor at the CIA.
Clancy often played off — and sometimes anticipated — world events, as in the pre-9/11 paranoid thriller "Debt of Honor," in which a jumbo jet destroys the U.S. Capitol during a joint meeting of Congress.