The Invaders team consisted of Marvel's Golden Age superheroes fighting the Nazis during World War II. There was the original Human Torch (the android, not the later Fantastic Four member), Captain America, and the Sub-Mariner; in addition, the Torch's teenage partner Toro and Cap's sidekick Bucky were considered part of the team. The project was the brainchild of Marvel writer/editor Roy Thomas, who had loved Golden Age comic books since childhood.
The team first appeared in Giant Size Invaders #1 from June of 1975, but quickly jumped into their own series and took off with a variety of 1940's-era adventures, and facing a variety of enemies. Thomas did his best to make sure the continuity within this series coincided with Marvel's 'established' WWII fictional-history, and often this required glossing over a few details as originally published decades before; but for the most part the team was left to wander freely.
Highlights of the series include appearances of the superhero team The Liberty Legion along with the introduction of the British hero Liberty Jack, as well as the re-introduction of a number of Marvel's Golden Age superhero characters who had been largely forgotten. Villains included the U-Man, and such goofy characters as Brain-Drain and the Blue Bullet (whose super-clunky costume actually resembled a bullet); perhaps the best baddie from the series was the Nazi vampire known as Baron Blood.
But the series wasn't to everyone's liking. Several issues consisted of partial reprints, of stories from the World War II era of Marvel (or Timely, as it was known for a while) comics. The first artist on the title was Frank Robbins, whose style was a bit too sketchy for most. Also, the rather antique setting of the stories prevented some readers from fully getting into the book's continuity.
In any case, the title had a pretty good four-year run, and while not perfect, it was one of the better comics on newsstands during the late 1970's.