Near the end of the movie we see the Stingray being chased by the Dallas underwater. The Dallas overtakes the Stingray and prepares to fire torpedoes. The captain of the Stingray (the diesel) surfaces his boat and starts to make a run for the harbor.

In the following sequence, we see the nuclear submarine also surface and make to chase the smaller diesel. However there's a problem with that. WW2 Diesel submarines could make around 20 knots on the surface, running flat out. That translates to about 25 miles per hour. Doesn't sound like much, but trust me, it's fast.

The Nuclear submarine on the other hand, is lucky if it can make 25 knots on the surface. That's roughly 28 miles per hour. Meaning that there would be no way for the Nuke to actually catch the smaller diesel submarine.

However, when submerged, the Nuke could make a good 35-40 knots.

This begs the question. If the admiral (in the movie) is as experienced as he is. What would possess him to surface, there by giving up all his speed?