And the military doesn’t say one thousand five hundred thirty like this clueless OP says. They say fifteen thirty. And the reason they don’t speak in 12 hour time like civilians in many countries, is because saying, “we need you on the left flank by 1530” is more efficient and less ambiguous than “we need you on the left flank at 3:30, over.”
“Wait, do you mean am or pm?”
“-m”
“I didn’t copy, you broke up”
Etc etc.
EDIT also I forgot to mention, 1530 is quicker and more efficient to type on a typewriter or teletype than 15:30. As long as everyone is on the same page, but orders would also have a date to correspond with the time, so it is pretty obvious.







I got out of the military and switched to 12 hour time when I was living a pure 8-5 work life. Now I work, and work with people at all hours, so I’ve switched back to 24 hour time, though I still speak in 12 hour time. If I’m scheduling something, it is in 24 hour time. If someone asks me what time it is, I’ll look at my phone and it will read 17:00 but I’ll say 5 without blinking.