Today, if you want to send a message to a distant location, you’ll probably send an e-mail or a text message. But it hasn’t always been that easy. Military commanders, in particular, have always needed ways to send messages and were early adopters of radio and, prior to that, schemes like semaphores, drums, horns, Aldis lamps, and even barrels of water to communicate over distances.
This is a companion discussion topic for the original entry at https://hackaday.com/2024/03/14/retrotechtacular-air-mail-for-the-birds/