To be fair... a lot of the popular WWII aviator-heroes had problems after the war, and faded in popularity. Spy Smasher became (ever so briefly) Crime Smasher. Hop Harrigan, in All-American Comics #78 (Oct. '46) turned into a superhero named the Black Lamp. Airboy and Blackhawk proved to be the exceptions, and seemed to be more popular after the war than ever. Fawcett's Captain Midnight comic book had always been slanted as more of a superhero than the original radio hero he was based on, so it's not surprising that he should lean into the science-fiction vein. Superman didn't even have many science fiction adventures until after the war ended. In a way, Fawcett's Captain Midnight was a few too many years ahead of its time -- by 1951, a couple of years after Captain Midnight ended, Fawcett was publishing the very similar character Captain Video, another inventor-hero who fought alien villains.
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Captain Midnight in Outer Space