Nothing ought to better demonstrate my thesis as to the dominion of the "urban avenger" hero-type during the Golden Age of Comic Books than the fact that although comic-book publishers were not averse to spotlighting teams of heroes, few were superhero teams.
The most numerous form of Golden Age teams were the "kid-gang" teams patterned loosely after Warner Brothers' cinematic franchise "The Dead End Kids." Simon and Kirby's "Newsboy Legion" remains the most famous of these moppet-mobs, but other publishers came out with the Young Allies (Timely), the Boy Heroes (Harvey), the Little Leaders (Holyoke) and the Little Wise Guys (Lev Gleason).
Second runner up would probably be affiliations of heroes who had some grounding in either open warfare or Foreign Legion-like activities. This included the Blackhawks and the Ghost Patrol, and I would assume the genre of war comics-- on which I'm no expert-- had some ancestors to Silver Age creations like "Easy Company" and "Howling Commandos." Simon and Kirby even managed to combine the two subgenres-- war-action and kid-gangs-- into one feature, "the Boy Commandos." Harvey Comics came out with a "Girl Commandos," but these were all full-grown women and emulated the Blackhawks more than the Simon and Kirby creation.
But though there were occasional short-lived teamups of superheroes in this or that comics-story-- most of them originating either at Fawcett or Timely-- only three superhero team-features showed up on a regular schedule, and one of them was cancelled after two issues.
One of these is 1945's THE MARVEL FAMILY, which, at least in its early issues, regularly featured teamups between Fawcett's Captain Marvel and his two epigoni.
Though one might see MARVEL FAMILY's all-in the-family orientation as an anticipation of one Silver Age creation, Lee and Kirby's FANTASTIC FOUR, 1940's JUSTICE SOCIETY OF AMERICA unquestionably provided a more integral model for superteams of the Silver Age and afterward. To be sure, the earliest meetings of the Society were barely true "team-ups." The first issue showed the heroes having completely separate adventures-- in other words, the producers were keeping things in this feature pretty much the same as they were in any DC anthology book. Thereafter, the heroes had separate adventures against different manifestations of the same overall menace. Eventually some later adventures even dispensed with separate-but-roughly-related adventures, so that the heroes remained in a team as they battled the villains of a given story.
Finally, in the year after MARVEL FAMILY's debut, the "All Winners Squad" debuted in the last two issues of ALL WINNERS COMICS. The Squad generally followed the pattern of the Justice Society, with the heroes having separate adventures against some common threat before coming together for the finale.
All of these groups, like those in the kid-gang and war-action genres, conformed to the pattern of the "urban avenger" type. There was little in the way of extrapolating the nature of the heroes or their universe that one usually saw in the "miracle hero" type as promulgated in prose science fiction and fantasy, though occasionally Fawcett's Marvel Family characters elaborated smatterings of new information about the wizard Shazam and his past history, as in the introduction of Black Adam (MARVEL FAMILY #1, 1945).
The first hero-team of the Silver Age, however, would be one of the first features to fuse the two heroic types, and will be discussed further in Part 3.
ADDENDUM: I belatedly confess that I completely forgot one other regularly-published team feature: 1941's all-male SEVEN SOLDIERS OF VICTORY. Mea culpa.