Nice! Around 1970, a friend worked for Western Electric at the underground cable termination in San Luis Obispo CA. A coaxial cable to Hawaii landed there. They had vacuum tube repeaters on the cable. They applied 3 kV of opposite polarity on each end of the cable to power the repeaters. As I recall, the building was 3 floors underground and mounted on springs to survive earthquakes and nuclear explosions. One floor, I think, handled government communications, while another handled public communications. This was all frequency division multiplex. I remember hearing "money chatter" on long distance calls when I was a kid as you heard the adjacent channels of the FDM. The SLO facility also had TASI that interleaved fragments of conversations onto the channels to increase channel usage. It was a sort of analog packet switching, though I suspect the "packet" routing was over a separate supervisory channel instead of in a packet header. I understand that the cable was eventually given to University of Hawaii for some oceanic research. Meanwhile a LOT of fiber optic cables now land in San Luis Obispo.
Harold