The Twelve is a group of independent mystery men that helped win World War II in Berlin with other superheroes like Captain America, Namor and the Invaders.
The Twelve is not an actual team, they were twelve mystery men who gathered together to search through the S.S. headquarters for any snipers or other Nazi soldiers. While in the headquarters, the mystery men were ambushed and fell through the floor into a secret tunnel. While in there, a Nazi leader injects the tunnel with gas to knock them all out. The Nazis then put the twelve heroes in cryogenic chambers so they can be medically examined for their super powers.
Russian forces invaded Berlin at the same time and were able to defeat all of the Nazi scientists and directors that were involved in the apprehending of the twelve superheroes. Due to this fact, the heroes have remained in their cryogenic chambers, forgotten to everyone else.
In the present day, a construction site has been formed over the tunnel that the twelve have been isolated in when a construction vehicle falls into the tunnel. The American government is able to claim possession of the twelve mystery men and try to manipulate them into working for the government in this post- Civil War society.