This facility is what's called a tandem office in the old long distance telephone network here in the US. The idea was that it formed a link in a routing chain

This facility is what's called a tandem office in the old long distance telephone network here in the US. The idea was that it formed a link in a routing chain between two end offices when a long-distance call was placed. Cheshire, CT, also happened to be an AUTOVON site, which carried with it military and national security significance. This is why it was hardened against nuclear attack, including the air handling augmentations, decontamination shower, gamma ray detection equipment, and so on.