SC-901 and the 900 series as a whole were the prototypes designed around 1961 by Stromberg Carlson. They were typically installed in ICBM silos and you will see them in some of the photo collections on the web. For example, that silo south of Tucson, Arizona, now a museum, still has them in place. Presumably SC- means Stromberg Carlson. Geoff WB6NVH