Revealing mistake: In the scene where Jack Ryan is brought aboard the U.S.S. Dallas after releasing himself from the helicopter, two crewmen drag him inside. The crewman on the left side of the passage backs into a metal valve, but the valve moves down and left, then snaps back in place as if mounted to a rubber pipe.
Revealing mistake: None of the exterior storm scenes where rain is present have any visible impact on the actors. No water or mist on face, binoculars, hat brims, etc. The special effect that creates the rain does not correlate to the either actor appearance or background reality - sun reflections, clouds, etc.
Revealing mistake: Near the end of the movie when the Russian attack sub gets hit with the errant torpedo, the shot from the "Ruben James" shows the explosion from the surface. In the middle of the large wave generated is the puff of black smoke and a pyrotechnic flash which triggered the explosion.
Revealing mistake: In the scene where Ryan is chasing the undercover KGB agent through the missile compartment one of the valves on the missile tubes is very wobbly as it is bumped. Although given the state of the Soviet Submarine Force maybe this is accurate....
Revealing mistake: In the scene where they are dropping Ryan from the helicopter to the submarine, you can see that they used the same actor for both the pilot and the co-pilot of the helicopter. You can see the mirror image on the helmet of the pilot in one of the shots. It appears they just changed the voice actor only.
Revealing mistake: Near the end, when Ryan and Ramius are talking, right before Ryan says "welcome to the New World", Ryan is facing Ramius and his thick hair should be blocking the hill in the distance behind him, but his hair is translucent and the hill is visible through his hair. (02:06:00)
Chosen answer: They use it to wipe the grease pencil markings off the screens.
We called it "the Duty Roll."