In an earlier post on anchoring, I alluded to a sound-powered phone circuit between the Bridge and the Forecastle. Sound-powered phones are telephones designed to take their power from the energy of the incoming sound waves. While the handsets and headsets had receivers and transmitters, they were really bidirectional in that you could, if you wanted to, listen and talk over the same unit.
The advantage of sound-powered phones was that they were dirt-simple and they didn't require power. All you had to do was string two wires and hook a handset up at each end. For example, as part of the rigging lines between ships during underway replenishment, two sound-powered phone lines were sent across to the two ships could talk Bridge-to-Bridge and Unrep Station to Unrep Station.
All installed circuits were designated with at least two letters and then maybe numbers. For this post, I am focusing on the maneuvering circuit, the 1JV. In open-ocean steaming, the 1JV connected the Bridge, Main Control and the After Lookout. On the Bridge, the Lee Helmsman served as the phone talker; in Main Control, the Throttleman did.
Coming in and out of port, there would be more stations on the 1JV. For mooring alongside a pier or another ship, the Forecastle would be on the line, while the After Lookout served as the phone talker for the Fantail line handlers. If boats were to be operated, the boat davit stations had phone talkers.
Communications could be slow. The Conning Officer would give an order, such as "Foc's'le, Bridge, slack Line One." The sailor on the Lee Helm would repeat the order, verbatim, and the phone talker on the Forecastle would shout it out. The officer/chief/petty officer in charge would yell back: "Slack Line One, Foc's'le, Aye!" and that would be repeated back up the phone circuit. And if you had a couple of sailors as phone-talkers who were not exactly the sharpest knives in the drawer, it could be a real clusterfuck with lots of "say again" responses.
Back in the `70s, during the CB radio craze, a number of CB walkie-talkies began to hit the consumer market. Ships bought them, figuring that the Conning Officer (or the Captain) could then talk directly to the person in charge of the Forecastle and/or the Fantail. All it took was to find an unused channel and use that. It was believed that as long nobody said their ship's name, that using the CB radios didn't compromise operational security.
This is no shit: A destroyer was steaming into the naval station at Roosevelt Roads, Puerto Rico. The ship was heading for an anchorage, and, like a lot of ships, they were using walkie-talkies. When the ship was at the right spot to drop the anchor, the Conning Officer keyed his walkie-talkie and radioed: "Foc's'le, Bridge, let go the anchor!"
That command was heard on two ships. The other ship was an oiler that was heading down the channel at Roosevelt Roads at ten knots. The Bo'sun's Mate on the Forecastle of that ship keyed his radio and yelled: "Let go the anchor, Foc's'le, Aye!" At that command, the sailor holding the sledgehammer at the pelican hook swung the hammer, knocked it free and all hell broke loose.
Fortunately, there were no injuries and nothing serious was broken. But an order went out from the type commanders, in very short order, outlawing the use of CB radios aboard ships.
 All included the letter "J", designating the circuit to be sound-powered.
 Not 9, the emergency channel or 19, most commonly used by truckers
It’s a fair question
15 hours ago