In the middle of the episode, Captain Crane and Ensign Kowalski leave the SEAVIEW in the flying sub which crashes underwater. Later in the episode, Kowalski again leaves the SEAVIEW in the flying sub with Admiral Nelson to rescue Captain Crane.
After Crane escapes the cave, the shadows on the beach disappear and reappear. This cannot be explained by clouds, because when the shadows are gone the sun brightly lights the beach.