Factual error: When Michael Douglas and the girl have just taken off in the plane, someone shoots at them with a machine gun. But the person is behind the aircraft, not at the side and so it would be impossible for the bullets to crack the side window.
Factual error: When Michael Douglas and his son (and others) are tied up in chairs, they pretend to fight and cut each other's bonds. The son says something like, "The one time my father came to Cub Scouts, I earned the Covert Action Merit Badge." But there are no Merit Badges in Cub Scouts; they are a part of the older Boy Scout program. (There isn't a "Covert Action" Merit Badge either, but that helped the movie along, so it's okay.)
Chosen answer: Designs of torpedoes dating back to before World War Two were generally capable of exceeding thirty knots, with many current designs easily doubling that and, in certain cases, reaching well into three-figure territory. The Juliet-class torpedo appears to be fictional, but, given the performance figures for real life designs, a speed of thirty knots seems actually quite slow.
Tailkinker