This here greatest moment never happened, cuz it was one of those imaginary stories. In 1977, Marvel started publishing "What If?" a series devoted to imaginary tales, each one being complete in a single issue. DC had done "imaginary" stories in their regular superhero titles for years, warning kids on the cover "Hey it's a Goldarned Imaginary Story!" to make sure they knew it wasn't in continuity. Well, ol' Mighty Marvel figured, if we got a whole series of tall tales, no one will get confused.
What If #3 (What If The Avengers Had Never Been?) was published in 1977, story by Jim Shooter, art by Gil Kane and Klaus Janson. I think this is one of Shooter's best Marvel stories, and it was enhanced by the Kane/Janson team. I always loved Janson's inks on Kane's pencils, and this effort was amazin'. The story takes place right after Avengers volume #2, where the Hulk said "I don't need to be a member of your little superhero club, adios!" This moment struck fanboys in their chest just like acid-reflux after eatin' a bag of Doritos. I loved the Hulk, I loved the idea of Hulk in a team. I always wanted to see the Avengers with the Hulk and never got this again until The Ultimates. That aside, what happened in Avengers #3? The Avengers go after the Hulk, the Hulk teams up with Sub-Mariner and nearly wipes them out. Only the Hulk changin' into his alter ego, Bruce Banner, brings an end to the team up.
In What If #3, the moment the Hulk leaves the Avengers, that's when Thor decides to throw in the towel and call it quits. Giant-Man and Wasp leave Tony Stark alone, who still realizes that leavin' the Hulk alone ain't a smart idea. Then Stark has a purty good idea, an idea so good they should have done it in the Initiative. He creates the Iron Avengers. Rick Jones, Henry Pym, and Janet Van Dyne, in different variations on the Iron Man armor. Jones' armor can phase in/out of objects, Pym's armor is super-sized for his Giant-Man form, and Janet's armor is super-small, but with high-tech stingers. But these guys are losers who can't even keep their own series goin'! They give up on the armor when they find it is too difficult to control.
Tony Stark decides to take on the Sub-Mariner and Hulk all by his lonesome superhero self. From here on in, it's all action in the mother of all superhero battles. Iron Man supercharges his armor and deep fries the Hulk in the ocean. That takes out ol' Greenskin, but the Sub-Mariner is in his element, and batters Iron Man to pieces. The calvary arrives when the Iron Avengers decide that those supersuits ain't so bad after all. They succeed in drivin' away the baddies, but only through Tony Stark's ultimate sacrifice at the end. It just brings tears to this ol' cowboy's eyes everytime he reads it. Nuff said.