Atlas I was an American expendable launch system, used between 1990 to 1997, developed by Convair to launch a variety of probes and satellites. The vehicle operated out of Space Launch Complex 36A and 36B at Cape Canaveral Air Force Station.
I recommend turning on "Advanced tweakables" in KSP settings.
To download each variant of Atlas I, go to the "Files" section.
Here are my other projects.
Atlas I
Atlas G
Centaur D