What did military commanders say before they said "fire"?

“Fuego” is also the Mexican word for “help.” As in what you shout if someone is attacking you. Whether it applies to other dialects, I don’t know.

All right then, so much for the Second Age. Let’s try the Third Age.
From your linked site, at Helm’s deep Aragorn gives the order “Tangado a chadad!” to the Elvish archers which is translated as “Prepare to fire!”

LL, no small Tolkien geek himself.