Nigel McKeand (Sonar), Ron Stein (Ray), Dave Dunlap (1st Mate)
There is a small physical blooper that was left in, either because it added a touch of realism or because they didn't want to waste time reshooting the scene. Crane and Nelson are in Nelson's cabin. As Crane turns at the knock on the door, his hand hits the telephone on the desk, almost knocking the receiver off.
The nuclear device is the same prop (with a few modifications) used to lower four men to the bottom of the ocean in "The Condemned" in Season 1.
Crane states clearly after the whale has swallowed the nuclear device that the killing zone is a fifty mile radius. However, when it does go off, the Seaview is extremely close, and it weathers the blast with a moderate lurch.
(Nelson is speaking to Crane about Holden)
Nelson: He's never been noted for his stability--most of the scientific community thinks he's, uh, a little bit touched. But, he's a genius.
Holden: You've seen what a mad whale can do. I assure you a mad scientist can be far more destructive.
This is the first episode to rely on stock footage of prior episodes (mostly Jonah and the Whale, but also including color-tinted footage of Submarine Sunk Here). Some crew members wear the first season uniforms so they could be integrated into the older stock footage.
Terry Becker appears in stock shots only. The actor did not wok on any episode of the season beyond The Sky's On Fire.
Kevin Hagen had a long career as a character actor, appearing in many television series in the 60's and 70's. He was a semi-regular on Land of the Giants (he appeared in ever Irwin Allen TV series in the 60'S). He his best known as Doc Baker on Little House on the Prairie. He would return to Voyage in the fourth season episode Attack!.
This episode is practically a re-shoot of Jonah and the Whale. A casual viewer might not even notice the difference.