Whenever books about the Civil War say that Grant telegrammed back to Halleck or Lincoln or whomever, I wonder specifically how that worked. Did they go to a specific telegraph office? Did it have physical wires running to another specific telegraph office? How did one telegraph office know which next hop to pick to get their telegram to the White House? Did they encrypt their telegrams? If they were encrypted, did they use some nonsense encryption like a basic substitution cipher? If they weren’t encrypted, what guarantees did they have that their telegrams wouldn’t be intercepted?
If Lincoln wanted to reply to Grant, how did he know where to send his telegram to? Did Grant have to tell him “write me back at Cairo, Illinois”?
If the South wanted to interrupt the flow of telegrams, did they just have to blow up telegraph offices? Cut wires? Did the Union patrol every foot of wire? If they couldn’t patrol every foot of wire (as I imagine they couldn’t), did they at least have some quick way to identify where breaks in the wire happened? If every telegraph office was directly connected to one or more other telegraph offices, then an easy way to check whether a nearby telegraph office was un-blown-up would be to send the neighboring telegraph office a heartbeat message (i.e., “hey, you there?”) every so often. If they don’t get a response, then run along the wire between this station and the neighboring station and check for breaks.
How about kidnapping telegraph operators, or just holding them at gunpoint, or getting spies to go work at the telegraph office? Were telegraph operators vetted for their loyalty to the Union?
A quick bit of Googling turns up this book, which probably answers all my questions and then some. Nice.