Crossing the Pacific during the night used to be a lonely stretch, once we got in the middle near Pitcairn it really did become a radio dead zone for a few days, just too far from anywhere.
My job as a Crypto Tech (Maintenance) in the Navy (CTM2) had me going out on destroyers for a few months at a time in the early 70's. Based in Rota, Spain we would install an equipment shelter on a ship while they were in the Mediterranean, and eventually had one on a destroyer in the Indian Ocean. Our gear was almost all receivers (VLF thru UHF) and a team of CT operators would monitor whatever there was in the area. We usually had 2 CTR (CW), 2 CTI (Linguists), 2 CTO (TTY ops) and CTT (other specialized systems) people on the team.
The CTR's worked port and starboard watches 24 hrs a day, usually copying Russian ships, or CW signals from local countries in Africa, some were police nets on CW. Being a ham that only used CW, I helped them by sitting their posit to give the ops breaks, once they taught me the format they used for copying all the signals on a mill.
For our own comms we tied into the ship URC-32 HF transceivers for our encrypted TTY transmissions to a Navy shore station, using the other sideband of the DSB transmitter. It was kind of like ZL1BBW in the Pacific, the Indian Ocean was a radio dead zone. The I.O. wasn't a very strategic area for the Navy and the shore stations (Rota and Guam) didn't have rhombics aimed there.
Our CTOs would cut tapes of signal reports to send to NSA and they would pile up for days at a time while the ship had no circuit with any shore station. I went to the radio room to see what the Radiomen could do and was shocked to find them using a frequency list and just trying each freq, going up the list with no regard for time of day or propagation. Trying to raise Spain or Guam from the middle of the I.O. using 4 Mhz in daytime, or 19 Mhz at night, at the bottom of the sunspot cycle! I tried to explain what bands would work but they had to go by some Navy procedure. We would go for a week at a time with no communications to the rest of the Navy. We were intercepting lots of new signals but couldn't send reports...
It was spooky being on a ship that far out and not having any 2-way communications. I could copy hams on the CW ham bands 24 hrs a day but the ship couldn't get a teletype circuit up.
Glenn AE0Q