This episode uses extensive footage from the film The Enemy Below (1957). Coincidentally, the film co-starred David Hedison as the destroyer's Executive Officer.
As the Flying Sub was destroyed in the previous episode 'Terror on Dinosaur Island', the Flying Sub in this episode must be a new one. It must be designated as FS-2. Yet, this is destroyed too and therefore a third one will have to be built for later in the series.
The sub captain asks the first mate how deep the bottom is, and he responds 1,200 ft. The captain orders the sub to 1,200 ft but the sub bottoms out at only 700 ft.
This episode takes place in the 1970s.