Continuity Error: When Captain Crane is on-board the enemy submarine, he's wearing black dress leather shoes, as seen in several scenes. Yet, during the fight scene with the captain of the enemy submarine, Captain Crane is wearing black sneakers with white sides (stained to look black) and bottoms. When comparing the shoes worn by these two submarine captains, it is obvious Crane is no longer wearing black leather dress shoes.
When Crane climbs aboard the destroyer, we see he's wearing shiny black leather dress shoes and the white soles with white sides stained black no longer exists.
Nelson gets on the intercom and tells Sparks to contact the Secretary of Defense. Good old Sparks comes back a few seconds later and announces that he has the Secretary of State on the line. The voice of Sparks was not that of Arch Whiting, who usually played our intrepid radio man.
Robert Yuro (Crewman), Rick Warwick and Paul Stader (Men)
For the second episode in a row, the Flying Sub has been destroyed while Nelson was piloting it; making the total three Flying Subs lost so far for the second season.
Re-use of footage made the submarine look the same leaking oil (or releasing oil as a trick) as it did putting out a "sonar decoy".
(Captain Ruiz has informed Crane that he shot down the Flying Sub)
Crane: So you're the one who's been picking up our missiles. Why?
Ruiz: You see, Captain, a very small country with a few nuclear missiles suddenly becomes a very large country.
The plot for this episode was lifted from the movie "The Enemy Below" (which starred David Hedison under his original moniker "Al"). It uses quite a few scenes from the movie that are edited in quite smoothly.