It used to be said you could tell when you were knocking on a bit when policemen started to look younger.

Now you can tell you're getting older when Ben Affleck, seemingly fresh from the cub scouts, is cast as tough CIA analyst Jack Ryan.

Harrison Ford brought a grizzled dignity to the role in Patriot Games and Clear And Present Danger, while Alec Baldwin made his big-screen debut as Jack in The Hunt For Red October.

Now Affleck steps into his shoes in a sort of prequel to the Ford movies where he's just about to begin his ascent up the Pentagon's greasy pole.

You can tell what sort of movie it's going to be as soon as a line of blacked-out people carriers and 4x4 jeeps snakes its way into a high security compound.

This is where a roomful of earnest old men trot out seemingly meaningless phrases such as 'passive nuclear strike', 'launch sequence' and 'Defcom Two'.

They are saying these things because an apparently hardline new incumbent of the Kremlin, President Nemerov (Ciaron Hinds), is rattling sabres.

When a chemical strike on the Chechen capital Grozny wipes out 80% of the population, US President Fowler (Cromwell) gets in a bit of a strop.

But when a nuclear explosion a bit closer to home wipes out an entire city the whole nuclear lexicon comes tumbling out. Defcom One anybody?

Meanwhile, Ryan, under the supervision of his CIA director mentor William Cabot (Freeman in Colin Powell mode) is building a completely different picture.

Rather than Nemerov, it appears a renegade neo-Nazi group, led by evil Richard Dressler (Bates), is trying to provoke America and Russia into Armageddon.

All Ryan has to do is persuade the White House hawks Nemerov is innocent - not an easy thing to do when your helicopter's just been brought down by an N-bomb.

Post September 11, the American view of mass destruction appears to have become a little less cosy and a bit more realistic.

For example, there's no hero stepping in in the nick of time to stop a digital clock seven seconds from a nuclear winter. The bomb here is real and people really do die.

For a good hour and half, director Robinson keeps the tension tightly screwed - but when the two superpowers begin squaring up to one another, reality is left behind.

While making some telling political observations and showing all-too-rare American humility along the way (Pearl Harbor?), at the end of the day it's just a serviceable thriller.