On their way back to the Jupiter 2 from a fishing trip, Will and the Robot come across a rusted robot. Will eagerly shows the find to his father and asks permission to repair it. John agrees, thinking it would be a good project for Will. The Robot is not at all happy, warning that Will should not touch the device nor attempt to repair; he explains that it is in fact a robotoid, that is, a cybernetic mechanism capable of free choice. Will assumes the Robot is just jealous and ignores him, setting to work on the repairs. Over the next several days, Will works hard to fix the robotoid, putting him back in working order. He catches the Robot trying to attack the robotoid with a hammer and is quite upset. When John asks why the Robot would do such a thing, he says that he wants to destroy the robotoid because he does not like it.
When the Robotoid is back in full working order, it proves able to perform many complicated tasks beyond the Robot's abilities and everyone is very impressed by it. The Robot feels very depressed as there is very little for him to do anymore. At night, the Robotoid goes off to make secret transmissions to his alien builders, telling them of his progress in subduing the Robinsons. When he has rendered the family helpless, his alien masters will come to the planet to take the Robinsons away for experimentation.
The Robot confronts the robotoid, telling him to leave, but the robotoid is far more powerful and easily disables the Robot. When Smith finds the Robot damaged the next morning, he heaps only insults at him and suggests he run away and destroy himself. The Robinsons miss the Robot after he is gone, particularly Will, who has begun to wish he had never repaired the robotoid.
The next day, the family discovers that the chariot has been damaged, the guns are missing from the weapons locker, and the force field is not working. When John confronts the robotoid, it informs him that he is now in command and that there is nothing anyone can do. Don and John try to attack him but he easily overpowers them. Will realizes the Robot is their only hope of rescue and manages to run away to find him.
When Will locates the Robot, he tells him what has happened and begs him to help. The Robot agrees to do what he can, but he is weak from not having been recharged in so long. He and Will come up with a plan to trick the robotoid. When the Robot and Will return to camp, the Robot pretends that he has betrayed the Robinsons and wants to serve the robotoid. Once he manages to get close enough, the Robot sets off a smoke screen to confuse the robotoid’s sensors; in the confusion, the Robot is able to destroy the robotoid. The Robinsons are very grateful, and are happy to have the Robot back with them. Even Doctor Smith is willing to admit that he was wrong, and gains a new appreciation for his mechanical friend.
- Although the DVD menus and various sources give this episode the title "The War of the Robots", the episode identifies itself as "War of the Robots", without the definite article "The".
- For the second time in the series music from "The Day the Earth Stood Still" is used for the theme of a character. In this case, the sinister music that plays over several of the Robotoid's scenes is the theme 'Gort'.
- The Robotoid utilized William Bramley to create its voice, and Eldon Hansen inside to give it movement. Bramley is also the voice of the Cosmic Life Force in "My Friend, Mr. Nobody."
- When the Robotoid calls his alien master on the communications device, the alien's image speaks but its mouth doesn't move, probably due to limitations with the prop.
- The final shooting script is dated February 5, 1966.
- The alien robot used is Robby the Robot, from several MGM SF movies. It made its premiere in the 1956 motion picture "Forbidden Planet".
- Robby the Robot will return in 'The Condemned of Space' as the Robot Warden, although he will not be voiced (and not as the same character in this episode).
- At the beginning of the episode, we see Smith, Will and the Robot fishing with make-shift poles of sticks and string. In the later episode “Blast Off Into Space” the Robinsons throw away several fishing poles. Why are Will and the others fishing with sticks and string when real poles are available?
- Why did the Robot attempt to kill the Robotoid with a hammer? Why not just blast him dead as he did at the end of the episode?
- If the Robotoid’s alien masters left him on the planet, why do they need a homing signal to get back there? Wouldn’t they already know where it was?
- Why does the Robotoid feel the need to announce that he’s dead?
- Where is Penny through this entire episode? Answer....Penny's inside the mirror. Angela Cartwright was filming "The Magic Mirror," while Billy Mumy was filming, "War of the Robots."
- This Episode was repeated on Thames Television on February 21st 1969
- This Episode was repeated on Granada Television on March 13th 1969
- "The mental capabilities of this machine are unlimited." Dr Smith says, as he places his hand on the semicircular rim on the Robotoid's face. When he says "He's simply devouring knowledge," the shot transitions from long to close, and Smith's hand is suddenly resting just above the Robotoid's arm.
- The Robotoid repairs Maureen’s damaged watch by hovering its claw over the mechanism. An obvious and clumsy cut and paste edit of the Robotoid’s claw is applied to show the before and after watch sequence.
- When the Robot is fighting the Robotoid, it receives a direct laser hit to the chest, but it miraculously survives unscathed! In a previous scene such a beam resulted in a de-activation of the mechanical man.
- Near the end of the episode, after the Robot says, "There is much we have to discuss," it proceeds to move forward. The tow cable attached to the rear of the Robot at ground level can be seen as it moves out of frame.
- This is the first episode in which the character of the Robot begins to become the more significant character it will be throughout the rest of the series. It's also the first episode in which the Robot says Will's name ("William Robinson" and then "Will.").