There's a scene in the book I'm planning (which is set in the late 30s or early 40s) where the FBI raid a house. Obviously, in a contemporary setting, they'd employ a SWAT team (yes, I know "SWAT team" is redundant since the "T" stands for "Team," but "SWAT" on its own just sounds odd) but according to Wikipedia, the first SWAT team wasn't founded until the late 1960s.
What I want to know is, what did the FBI employ in situations that called for the use of armed forces before SWAT teams existed. I've done some searching on Google and Wikipedia, but everywhere I've looked, including the FBI's official website, only describes what they did in that time period, not how they operated (I've also tried Googling the questions as phrased in the post's title, with even less success).
Did they cooperate with the local police department, or was there another special forces unit in the 30s and 40s that served the same role as SWAT teams? If so, what were their uniforms like? What weapons did they use?