Green Arrow, having spent some time reading through old League journals, allowed his detective mind to activate his knee-jerk reactivism. It seemed that the date the League was said to have formed was seven months prior to Hal Jordan's having become Green Lantern, much less his starting working with other heroes. Ollie felt like he'd been lied to, and let Hal have it, but the also-present Superman stepped up. "Okay, Arrow! You've caught us red-handed-- and I, for one, am just as glad the secret's out." Superman led the pair to a viewing room on the League Satellite, where Ollie watched a video recorded by J'Onn J'Onzz before he left the team. "As you listen, please understand why we had to hide the truth! It wasn't you we feared-- it was the times!"
J'Onzz related the story of his arrival on Earth in 1955, with much of the dialogue and layouts taken directly from
Detective Comics #225. Caught up in the McCarthy era paranoia of 1959, Jones had to deal with the arrival of his nemesis
Commander Blanx, with the invading Martians setting off a national panic. Jones was captured by the evil Pale Martians, leaving his future associates Flash, Superman, Batman, and Robin to investigate the goings-on. Roy Raymond, TV Detective, reported on incidents in Jones' city of Middletown, attracting a veritable army of contemporaneous adventurers.
Batman had this most super of groups divide into teams and spread out to monitor the globe. Jimmy Olsen, Plastic Man and the Blackhawks chased a red herring that led them to nearly discover Rip Hunter: Time Master and his partner Jeff's secret operation. Lois Lane, Robotman, Congo Bill, Vigilante, and the Challengers of the Unknown nearly foiled Adam Strange's catching a Zeta-Beam back to Rann and his ladylove Alanna. Only the World's Finest trio, Wonder Woman, Flash, Aquaman, Roy Raymond and Rex the Wonder Dog headed in the right direction. It seems Ferris Aircraft was involved with a satellite launch at Cape Canaveral, and a test pilot on site, Hal Jordan, had been shot from ambush by a ray-gun. Everyone was impressed he was still on his feet to show the lot where the dirty business had gone down.
At the launch pad, Rex scented trouble, so Superman used heat vision to flush the invisible Martians. "Hera help us! It's raining Martians!" Commander Blanx put up a decent fight against Superman. Wonder Woman enjoyed pitting her Amazon strength against the aliens, while Flash helped Aquaman with a hydration issue, giving the Sea King power enough to flatten a Martian. Robin noted water-droplets on the rocket took the form of a once "invisible man," so the caped crusaders climbed up to gently release J'onn J'onzz. "Thank you, my friends! Had you not intervened, I would have been shot into space with this satellite tomorrow-- to my death!" Robin asked, "Gosh! But aren't you a Martian, too!" J'onzz J'onzz confirmed, "I am, lad-- yet not a Martian such as they! And to prove it, I'll tell you the most closely-guarded secret to any Martian-- our one fatal weakness!" One reveal, and heat vision did the rest.
The Pale Martians were sent back to their home planet, while the benevolent J'onn J'onzz was allowed to stay on Earth. Aquaman, Wonder Woman, and Superman all agreed that given six months for things to calm down, and with their full support as a club, the Martian Manhunter could be accepted by the public as part of a new group they thought about forming. Batman wished to remain a loner, which didn't work for Flash. "But, Batman-- a league against evil! Our purpose would be to uphold justice against whatever danger threatens it!" Superman also asked that the Caped Crusader take time to think it over, while Raymond did his part by vowing to a press blackout on the affair.
"And so it was decided! All of us swore silence!" The world chalked the Martian invasion to mass hysteria. "It was several months after-- when I lost my ability to use my powers while invisible-- that we had our first official case-- the case we maintained first brought us together! Of course, Robin, Roy, and Hal weren't members-- but a new hero, Green Lantern, was! Still, we've always celebrated the original day! I hope, now, you understand-- because it opened this world for me!" Green Arrow felt he should be "teed off," but knew "It was a nice thing you did for Ol' J'onn! I'm kinda sorry I missed him when he was on Earth recently! Now lemme outa here! I got somethin' in my eye!"
Steve Englehart, Dick Dillin, and Frank McLaughlin created one of the most influential DC Comics ever with this tale. While retroactive continuity was nothing new even then, writing such a massive crossover of isolated features into a pre-origin tale filled with cross-referenced minutia, "first meetings," and other rampant revisionism? This was truly the Marvel Age of DC Comics! A truly great work, and as such endlessly copied, but rarely duplicated.
For a much more detailed version of this story from the Martian perspective, look
here.