This is, I believe, the first Hollywood cartoon to feature a theme of alien invasion and it came eight years after Orson Welles' famous "War of the Worlds" radio broadcast. There were, of course, earlier cartoons with depictions of travels to Mars (e.g. Max Fleischer's Koko the Clown cartoon, "A Trip to Mars," from 1924) and the moon (e.g. Fleischer's "Dancing on the Moon," from 1935) and at least one cartoon I know of that referenced Welles' broadcast (Bob Clampett's "Kitty Kornered," also 1946), but I don't know of any others before this one that actually depicted alien invaders, either on another planet or on Earth. (In Fleischer's earlier Superman cartoons, the threats were always earthbound.) There was renewed interest in this theme after the war as reports of UFOs, or "flying saucers" as they came to be known after 1947, began to increase.
The director here is Bill Tytla, a former top animator with the Disney Studio who was renowned for his work on SNOW WHITE, PINOCCHIO, FANTASIA and DUMBO, and one can see his considerable talent in the overall design of this above-average postwar Popeye entry. The color process used here is the two-color process, Cinecolor, and not Technicolor.