So I'm thinking about an underwater civilization and everything related to it, and I got to thinking about how they would communicate over extremely long distance.
I knew that underwater species like whales and dolphins can communicate over a really long distance through vibrations and sonic waves and whatnot, but I'm focusing on what happens when they start to develop their counterpart of our telephone and radio. More so, how would it work in places without water when they eventually go beyond their natural underwater habitats.
Human vocalization wouldn't work underwater or in space, so in place of that, we developed things like extremely low-frequency transmission for communication with submarines. Would they need to build something like a room filled with water to send out their transmission?
I'm trying to have them come on land and enter a conflict with land species such as ourselves, which is why I am trying to figure out how they would communicate, since going underwater and yelling wouldn't really work when they push further inland, and definitely won't work when they start going into space.
I'm not as concerned for their past conflicts in the classical/medieval/renaissance era, I just assume they'd send messengers and letters and such. But I am open to interesting ideas if something does show up.