Appearance: Daring Mystery Comics #2 (February 1940).
Golden Age Appearances: Daring Mystery Comics #2, #4-5.
Modern Appearances: None.
Years Active: 1941-?
K-4 and the Sky-Devils are a group of heroic fighter pilots, like (most notably) the Blackhawks or Timely's own Captain Daring (II) & His Sky-Sharks. Timely never had much luck with groups of heroic pilots--really, only the Blackhawks showed any staying power out of that set of heroes--and like Captain Daring (II) K-4 and the Sky Devils disappeared after three issues and were never seen again.
K-4 and the Sky Devils are, needless to say, active in the fight against the Axis, flying Grummans against the bad guys. K-4 is Captain K-4 (real name never given), a "flying spy and soldier of fortune" who had 11 victories in WW1, "triple that with the loyalists in the Spanish rebellion, and dozens more in the China-Japan conflict." (Yes, I know that most of you read the preceding in the image of K-4 on this page, but there are still some folks out there who don't load images from web sites.) (Besides, I need to pad out the text on this page.) The Sky Devils are Lt. Ronald Wolverstone-Clodd, and Lt. Rene D'Auvergne, and if it seems like naming two men "the Sky Devils" is a bit excessive," well, I agree with you. Lt. Wolverstone-Clodd is an uninteresting British pilot with no background to speak of. Rene Lt. D'Auvergne is a "French World War ace and expert swordsman."
The trio have no superpowers, but they are expert fighter pilots and good brawlers.