The word “fire,” meaning “make your long-range non-thrown missiles go at the enemy” seems likely derived from aptly named firearms, and most European languages seem to have a similar metaphor. However, what did, say, Welsh longbowmen get told to do? Yes, of course, I know whatever it was probably had a lot of w’s and y’s in it, but what metaphor did they use? Loose? Shoot? Let fly? (Not “pluck yew.”)
Just IMO, but I would imagine that using bows, the most practical command to fire would be whatever word they had for ‘release’ or ‘let go of the damn bowstring’ 
etc since they are probably already holding the bow in the drawn position and aiming.
Were archers more effective when they were all firing in sync, or in a fire-at-will situation? I imagine if you have everyone firing at once, a lot of people are going to be aiming for the same target, which would kind of waste their shots I’d think.
AFAIK they didn’t aim for targets, rather they aimed for an area, so if they all fired at once, a whole area would be decimated at once.
I think “loose!” is the command to release your arrows for english-speakers… Here’s a site with a glossary of archery terms:
http://www.centenaryarchers.gil.com.au/archery_terms.htm
EZ
“Charge!!”
“Kill the Frenchies! Kill the FRENCH-ies! Kill the FRENCH-ies!”, Elmer Fudd style?
For the first cannon I believe the term (in English at least) was “give fire”, since the charge was lit using literally a flaming brand or red-hot iron.
Smoke! :D:
Ready…
Aim…
Cannons date from what, the 1300s? They may have exploded with some frequency, but that’s still a lot of warfaring going on for the non-blackpowder types to get used to hearing the word “Fire”.
That being said, I had a religion teacher who posited that early Hebrews charged into battle screaming “Yahweh”, kinda like “yahoo!”
ymmv.
As a slight aside, what do they say in other languages? For example, I don’t even know if “fire” is a noun or a verb in its use in English. I say this because I know that in Spanish (in Mexico anyway), they always shout “fuego” which is definitiely a noun, and strikes me as wierd, 'cos I’d always imagined that in English it was a plural, understood-you, imperative.
So, maybe what they say in other languages would help trace the answer to the OP?
I believe in German they say Feuer Frei, translated as fire freely/at will.
I read every novel in the series of Master & Commander and one of the things that interested me most was that Capt. Jack always said only two things with regard to commands: Make it so, and Let it be done. I think he said that because those sentences were the least likely to be confused in the noise of battle - and they are pretty damned unequivocal too. I wish I could tell my employees “Let it be done!” and “Make it SO” Beautiful.
But in German, that’s a noun (like in Spanish) rather than an imperative. However, now that you mention it, “fire freely” is definitely a verb due to the adverb (whereas we could still argue that “fire at will” isn’t an imperative but a noun usage).
But “fire” is still common, so we’re not closer to the OP…
I agree 100%.
The Elves apparently said:
“Fire the arrows!”
The OED seems to think that the verb form of the command “fire!” started out life as the noun, perhaps as “give fire.” The French parrallels it with faire feu.
Of course, an archer predating cannons/guns might have had a different word.
Presumably, only the flaming ones though.
Actually, that translates to ‘release the arrows’. From this site. Their explainations make more sense.
/LotR geek
In Russian they said “Ogon !” With a soft n. It’s a noun and it does still mean fire. I’m not sure when the russians got accustomed to this, whether before Peter I or after.