Torchwood doesn't deal with pirates. The only pirates Britain really has to deal with seriously are those that mess around in the Caribbean, and that's a different story entirely, and beyond the point. Because Torchwood is an organization devoted to protecting Great Britain (and the world, sometimes) from the alien threat.
Which is not pirates.
So why, then, when the flag of the Revenge, the ship of the Dread Pirate Roberts, who never leaves a captive alive, was spotted a few miles off the coast of Swansea, was it apparently up to Torchwood Three to deal with it? Nevermind that they had enough supernatural problems to be dealing with, what with the rift grabbing people and spitting alien things out all the time. No, clearly the very deadliest of pirates fell under their district as well. That's sensible.
And clearly they should send the immortal man to deal with the deadliest of pirates. Yes, that just makes sense.
Unfortunately, Jack realized a moment later that it actually did.
Sighing, and resigning himself to losing a couple more lives in the process, Jack sailed off in a gold-painted dinghy to draw the attentions of the Dread Pirate Roberts. One of these days, he decided, he was going to be in charge of Torchwood Three. And things would be different then. He wouldn't have to keep dying for Queen and Country on a planet where he was technically an alien.
Jack raised a merchant's flag as he approached a large, dangerous looking vessel. A moment later, the vessel raised a very unconvincing looking imitation of his own flag. How did this guy manage to have such an awful reputation, if he was this incompetent?
Still, he was supposed to infiltrate and eliminate, rather than just exter - erm, blow up. So he paddled up, wares prominently displayed on deck, and acted incredibly surprised when, instead of fellow merchants looking to trade, a bunch of pirates jumped from one ship to the other.
"Oh help, someone, please, anyone, save me."
No one had ever called Jack the best of actors.
He was tied up and carried over a brawny man's shoulder (which on any other day he might have enjoyed, but not today) onto the Revenge and presented to Dread Pirate Roberts for inspection. And, most likely, death.
"You aren't very smart, you know."
Not exactly what he'd been expecting to hear, but. "Oh? How do you mean?"
"Well, running around in a gold-covered little dinghy in this depth of water, carrying valuable merchandise, is just poor sense. You've no way of protection either yourself or your goods, and frankly, it's just screaming for you to be attacked."
"You don't say."
"Really, I don't know why you didn't just surrender. I'm sure you've heard of me? The Dread Pirate Roberts?"
"The name has come up occasionally."
"Then certainly you know that I don't allow my prisoners to survive?"
"I might have heard something like that."
The pirate frowned. Jack's head had been forced to the deck by swordpoint, but he could just hear this ridiculous pirate frown.
"You're an odd one..."
"Jack. Captain Jack Harkness." The sword moved away from Jack's neck, and he sat up to look at his captor. Really, not a very impressive sight. Not very pirate-like at all.
"Well, Mr Harkness, I think I shall keep you."
"...I'm sorry, keep me?"
"Yes. You'll make a fine personal attendant."
And so, Jack's life on the Revenge began.
Of all his jobs in all the strangest and most interesting places in the known galaxy, and what he could remember of his days in the Time Agency, working as the Dread Pirate Roberts' personal assistant was undoubtedly the most boring. The pattern was the same: each day the crew would shout and sing songs while keeping the ship on track, each day they would come across some merchant vessel that would, on sight, immediately give up their goods to avoid capture, each day the crew would feast on their share of the goods, and each day Jack would have to stand just-behind-and-to-the-right of Roberts and fulfill his every request.
And every night, just before he was sent off to his bunk, Roberts would say to Jack, "Good night, Mr Harkness. Good work. Sleep well. I'll most likely kill you in the morning."
And every night, Jack would reply, "It's Captain Harkness, and I'd like to see you try."
(Jack gets off the ship eventually, after having learned the secret of the Dread Pirate Roberts and asking him to please, stick to pirating in Guilderian-Florinian waters, as Britain did not appreciate the stealing and robbing, and only had so much to go around. Roberts, who is in fact Pierre, sets off as first mate to the next Dread Pirate Roberts with a ship of British crew, promising never to return to England's shores again.
Jack calls it a job done, and never speaks of it again.)