Though you can't see the cannon crew I'm working with, you can see the next crew over. A cannon crew includes the fellows you see hovering around the gun in the background, whose job it is to clean, load, and fire the weapon. The crew includes one more person--the matross who minds the ammunition box, affectionately dubbed the powder monkey.
In this photo, I am the powder monkey.
It sounds like an inglorious job, and it is less exciting (in my opinion) than working on the gun itself. You're away from the main action, you spend a lot of time crouched by the ammunition box (it's killer on your ankles), and if the gun is overrun or surrendered, you have the unfortunate job of running the ammunition box off the field. I have run that box off the field so many times I could stab someone with a ramrod. I am still waiting for a weekend--just one--where at least one wind sprint is not involved.
The powder monkey.
So, as you can see, it's a job with more grunt and less derring-do than the other positions. Yet it's still vital to the functioning of the crew, and is in fact somewhat of a specialist position. Each time the crew fires the cannon, they would fire a particular kind of shot (we, of course, just fire powder--we don't actually want to maim the other side). Depending on the situation, the gun commander may find it wise to fire a solid shot, or canniser shot, or bar shot, or grapeshot. And who needs to know what each of those looks like, and deliver it promptly and correctly?
Yes, the powder monkey.
I have, by the by, no evidence that this term was used for field artillery in this period (my only evidence for "powder monkey" is shipboard--but I further confess that I have done very little research into the term). However, we use it freely in reenactor-speak, a language that also includes euphimisms for PortaPotties and inauthentic cookware.
In a moment of vanity, I have to confess that I love this picture of me--the murky black-powder smoke in the background, the crisp blue of the gown, the rakish way the powder box strap cuts across the gown.