First Appearance: All Winners Comics #19 (Fall 1946).
Golden Age Appearances: All Winners Comics #19, 21.
Modern Appearances: What If v1 #4, She-Hulk v2 #22, Citizen V & the V-Battalion v1 #1.
Dates Active: 1946-1949.

The All-Winners Squad was Timely's first true superhero group; rather than being a pre-made group, like the 3Xs, the Squad was put together with previously independent heroes, ala DC's Justice Society of America, and presented as a team. This attempt to duplicate the success of the JSA was not successful, and the All-Winners Squad quickly faded from view. In the modern era it has been referred to in various Marvel books on several occasions but has only been seen in action, as a team, twice. Nonetheless, they occupy a place of importance in the history of both Marvel Comics, as the company's first real superhero group, and in the diegetical, in-continuity, history of Marvel's Earth, as America's post-war superhero group.

The All-Winners Squad initially consisted of Bucky (II), Captain America (II), Human Torch (I), Miss America, Namor the Sub-Mariner, Toro, and the Whizzer. They were brought together because Harry Truman asked the Invaders, the war-time superhero group that the heroes had been members of, to continue as a unit but under a new name. In their first battle as the All-Winners Squad, in 1946, they fought against Isbisa, an Axis spy. In their second adventure they fought against Madame Death and the time-traveling villain Future Man (a villain crying out for a return during the modern day, perhaps as an alternate identity of Kang). In their third appearance, in What If v1 #4, Captain America (II) died in battle against the evil android Adam (II), and the Patriot stepped in to replace Captain America (II) as Captain America (III). In their fourth adventure, set in 1946 (still) and published in She-Hulk v2 #22, they were...well, I'll let the indefatigable Ronald Byrd tell the story:

In She-Hulk (vol. II) #22, we saw that in 1946 the All-Winners Squad (Captain America (II or III, I couldn't tell (and I'm not at all sure that Steve Gerber even knew about the transition); somewhere I got the idea that Cap II died around February of 1946, so it depends on when in 1946 the story took place), Bucky II, Sub-Mariner, Human Torch, Toro, Whizzer, Miss America) worked alongside the Blonde Phantom (II) (who was using a motorcycle to get around, something I don't remember her doing in her golden age stories) in an effort to stop gangster Dutch Rosenblatt from stealing an atomic bomb (a rather poor showing for the Winners, it didn't work due to the extratemporal interference of the She-Hulk and Wanda Mason (daughter of the BP), who had come back in time to find out where Rosenblatt had hidden/would hide the bomb in order to...well, that's a separate story).  Whether the Blonde Phantom was supposed to be a new member or was just helping out this one time is unclear; if the former, she's the only "new" member of the Winners we've heard about (aside from the fact that the Patriot served alongside Captain America II, something we of course never learned in the golden age but found out in What If #4).

Citizen V & the V-Battalion v1 #1 didn't show the Squad in action, but it did portray a meeting between the Squad and Roger Aubrey, aka the Destroyer, a meeting which led to the establishement of the V-Battalion. This meeting also showed the The Angel. being a member of the All-Winners Squad.