“Clark is the kind of guy who does the jobs nobody else wants to do,” explains the latter. “He’s very physical and can get in and out of places easily. He also speaks several languages fluently, which enables him to obtain all kinds of information. He’s the best there is, so Cabot picks him to teach Ryan about field operations, and then sends them on a clandestine mission to search for three missing Russian scientists. Initially, I think Clark is peeved that he’s got to baby-sit Ryan through this mission, but it ends up creating a bond between them.”

There are two keys to the success of the big-screen adaptations of Clancy’s work, all of which (like The Sum of All Fears) have borne the imprint of producer Mace Neufeld: accuracy of detail; and a firm basis in historical fact.

This film is no exception in either category. “When I read the script, I was struck by how smart it was, which is a touchstone of all the Clancy movies,” says director Phil Alden Robinson. “They’re smart action films. They’re about the issues of the real world, treated in an intelligent manner. In the post-Cold War world, with regional conflicts becoming more prevalent and the proliferation of technology and information, the threat of someone using weapons of mass destruction in a populated area has increased tremendously. This is a movie that shows the danger of how fear can drive our reactions and lead us to the wrong conclusions and responses.”

Clancy’s knowledge of the situation is based, of course, on real, first-hand experience. And Affleck wasn’t about to let that experience go to waste. “It was really important to me that Tom approve of my doing the role because he probably understands this character better than anyone,” explains the actor. “And it’s been a real pleasure to get to know him. He’s a very smart and interesting guy. I’ve spent a lot of time talking with him, and he’s given me great insight into the character.”

Affleck also spent time at the CIA’s famous headquarters at Langley, Virginia, being briefed by 25-year agency veteran Chase Brandon, and finding out just what working for the CIA entailed.

And, like many a Clancy character before him, the star discovered that a very small part of that work is spent in car chases and shoot-outs, and a great part of it sitting at a desk reading, thinking and exploring possible interpretations of events.

Morgan Freeman, with James Cromwell as the President of the US. Since Ryan is a Russian-speaker, Affleck had to learn his Russian lines phonetically - the hardest thing he’s ever done, he says.

“It was really interesting,” recalls Affleck. “It wasn’t some kind of cloak-and-dagger operation, but more like an office with a very diverse group of people - highly competent and very smart people - who are dedicated, patriotic Americans.

“Most people at the CIA aren’t spies,” he continues. “They’re individuals writing documents and postulating ideas. In some ways, the analysts at the CIA are very much like graduate students. What they do is collect intelligence and become experts on various people, countries and situations. And then they synthesise their information.”

The determination to be accurate at all costs involved extensive co-operation with various government agencies; the chance to film a wide range of state-of-the-art military hardware; and permission to use three CH-53 helicopters manned by a crack team of Marines for a scene where the President (James Cromwell) has to be rescued. The quest for authenticity even extended to the insistence that actors playing Russian characters speak proper Russian in their scenes with one another and with other actors (including Affleck) whose characters are supposed to speak the language.