Popeye and Olive pay a visit to the Technical Museum, where a jet-propelled spaceship is exhibited. Although visitors are welcomed to tour the inside of the ship, it is apparently fully fueled and has a hair-trigger ignition that has not been disabled. Innocently, Olive starts the engine, and the ship explodes into motion, right through the walls of the building and into the sky. At the last possible moment, Olive grabs a flagstaff at the peak of a skyscraper and saves herself, while Popeye is left aboard to rocket into space by himself.
There follows a series of clever spoofs as the craft zooms through the stratosphere and beyond: A hitchhiking crow is transformed into a roast turkey dinner on a platter; the Milky Way--which is revealed as a collection of milk bottles that spell out the words in script--is whirled into a wheel of Swiss cheese. The planet Venus appears as a women in a state of undress silhouetted behind a window shade. A Japanese stereotype peeks out from behind an eight-ball, a snarky allusion to that nation's crushing defeat in World War II.
At last we are shown the rocket's destination, the planet Mars. We are presented with a brief tour that demonstrates the warlike nature of the inhabitants and their predilection for supplying themselves with armaments: bayonet grass is being cultivated for its yield of actual metal bayonets, and grape shot, grown on vines and trellises, ripens into lethal ammunition.
As the rocket enters the Martian atmosphere, it is detected by an automated listening device and the planet is alerted. Here we are introduced to the denizens of this totalitarian world--little green men who function as mindless automatons, and their evil ruler, who towers above them, leaning on a sword in his red tunic. The strongman points to the sky and announces (in a reverberating voice), "It's an invader from the Earth. Bring it down!"
Unable to resist the forces mustered against him, Popeye is captured and placed in shackles. The emperor himself interrogates him: "How did you know that we were about to attack the Earth?" Lifting the "earthworm" effortlessly, the muscular monster scoffs, "If they're all like you, it'll be a cinch!" and proceeds to disintegrate the interloper with a ray gun. The iron shackles fall slack.
Next we see the preparations underway for the invasion. Vast armies march to a mothership, followed by tanks and a device called the "Earth Buster" which bears an unmistakable resemblance to a nuclear warhead. The scene cuts back to Popeye's prison cell, where we find that the Emperor's laser device was in fact ineffectual against a certain item stashed inside Popeye's shirt--his spinach can! The sailor scarfs down its contents and is instantly reconstituted. He breaks free of his manacles and is off to save the day.
Popeye's invigorated fist transforms a machine-gunner into a mild-mannered musician playing a calliope. An assembled regiment attacking Popeye with lances drawn is mowed down and magically assembles itself into an amusement-park carousel. Kamikaze planes dive-bombing the lone sailor are wrought into a benign airplane ride. And a tank firing missiles metamorphosizes, thanks to the power of spinach, into a Ferris wheel. Finally, with the remaking of this vast military-industrial complex into Coney Island nearly complete, Popeye turns his attention to the diabolical despot who had been within a hairsbreadth of realizing his ambition of an Evil Empire: One solid punch is all it takes to turn the "fearless leader" into a lowly skee-ball target.
In the final scene we see Popeye heading home in his rocketship, singing a ditty about the former 'collectivist dupes' now being "peaceful and happy, no more to be scrappy." Popeye has single-handedly saved the Earth!
- Rocket to Mars at the Internet Movie Database