Other mistake: The steamship shown in Patriot games is actually a shot from John Wayne's 1955 Sea Chase.
Suggested correction: The use of stock footage in movies is a common practice. More context would be needed to explain why this is a mistake.
Continuity mistake: When the terrorists attack the van at the bridge, shortly after the explosion, you see the terrorists crossing the water in a boat. In the background you can see the van on the bridge with its doors open, shortly after this the terrorists are at the van doors demanding that the police open the van doors!
Continuity mistake: In the final fight scene with Harrison Ford, the bad guy's hair grows longer then shorter then longer from shot to shot.
Factual error: Just before Sean Miller shoots the bookseller he takes the safety catch off the Ak-47. However, he moves the catch two clicks down and then fires the weapon on automatic. This is incorrect. For most modern weapons the safety catch feature goes safe-semi-auto, however the AK safety catch goes safe-auto-semi.
Suggested correction: I watched this scene twice to verify - there is only one click.
Continuity mistake: When the bookshop keeper runs from his store in Piccadilly he enters Aldwych tube station this is impossible as said tube station is a 20 minute bus ride away. Also when he gets on the train the conductor announces that the train will stop at Leicester Square, Piccadilly circus (were he just left from), and Oxford Circus This is impossible, as no train on the London underground makes stops at all those stations. He would have to change trains at Piccadilly circus.
Continuity mistake: When Jack rushes to save his wife and daughter from the terrorists on the freeway, there is a shot where he turns onto another road. Throughout this scene his seat belt goes from being buckled, to unbuckled quite a few times.
Continuity mistake: When Cathy Ryan enters the highway off Rowe Blvd (before the crash), she's supposedly heading toward DC. In fact, she continues back toward Annapolis instead of toward DC.
Visible crew/equipment: Early in the the film, after the attack in a shot with police tape in view, you can see a camera on a dolly along with the focus puller in the left side of the shot (wide screen version). (00:11:55)
Continuity mistake: When Jack Ryan gets in his car outside the Naval Academy to chase after the terrorists, he locks the driver's door as an officer comes up to the window to ask if he's okay. Moments later as Ryan is driving, the door is unlocked again.
Continuity mistake: When Sean Miller is being transported from the court, we see identical prison vans surrounded by Vauxhall Cavaliers. When the terrorists spring Sean from the prison van, the burnt out wrecks in front and behind the prison van are actually Rovers.
Continuity mistake: During the final boat chase, a fire is shown spreading in Ryan's boat around a green fuel tank labeled "100 Octane - low lead only." Seconds later, we see Miller shooting at a bright red tank labelled "Unleaded fuel only." 100LL is aviation fuel. Apart from that, the boat need only be carrying leaded or unleaded fuel - there's no reason for it to have tanks for both.
Continuity mistake: When Cathy Ryan is lying in the hospital bed, Jack gently strokes her forehead. The shot changes view, and Cathy's long hair is now in a different position around her neck and shoulders.
Continuity mistake: When Annette goes upstairs to the bedroom, we see a brief shot of her Uzi. There is no magazine inserted. Even the 10 round magazines stick out about half an inch and would be visible. When Jack picks up the Uzi after Annette is knocked out, suddenly, there's a magazine in it. (01:39:35 - 01:40:03)
Revealing mistake: When Sean shoots at Dennis the Bookseller's feet, puffs of sand do not erupt from the ground.
Visible crew/equipment: As the crossing guard moves out of the way and the van resumes chasing Kathy's Porsche, a dolly of equipment is visible on the grass on the left. There is no dolly present in the scenes preceding it that show the area. (00:44:45)
Continuity mistake: When the three IRA members go to Kevin's house, he shoots one through the glass in the door. When he is leaving the house a short time later, the broken glass has a different shape. (00:18:15)
Continuity mistake: After Cathy Ryan's car's back window is shot out, she swerves to the right toward a black Jeep with license plate 934-072, but the angle changes and when the car hits the Jeep its plate is THA-1L3. (00:50:30)
Continuity mistake: Near the beginning, a woman goes into an antique bookshop and hands the man who works there a battered book. At first, the book is the right way up, but when he puts it down it's suddenly upside down. When we see the book again, now it's the right way up.
Factual error: Lymington does not contain a rising bridge, only a small ferry to the Isle of Wight. It is only a small town, and not the built up area as presented in the film (the scene was filmed at Canary Wharf in London). Interestingly, the original novel is much more accurate with Clancy explaining in precise detail the route including highway numbers and towns the van travels through to reach Lymington, and the crossing is correctly undertaken on a ferry, not a rising bridge as depicted in the film.
Character mistake: When Greer and Cantor visit Ryan's home after Miller's escape, they state that he was being moved to HMP Albany on the Isle of Wight (correct, given it was a Cat A dispersal prison at the time and regularly used for IRA prisoners) however Greer later states "it happened in Kent, near the channel", which is incorrect. Lymington (as stated by the guards over the radio in the escape scene) is in southern Hampshire - over 90 miles away from Kent and on the other side of the country.