Sherlock thinks that over quite carefully, regardless of how utterly and completely ridiculous the entire thing is.

"No idea. Doesn't matter." Well, it does, a bit, but leadership sounds dull, after a fashion. Sherlock is delighted when people listen to him and thinks that they should at all times, but institutionalizing that implies responsibility, which is neither one of his strong points nor one of his particular interests.

"Navigator," he says. "Cannoneer, First Mate – or Captain too, don't care." As long as it's something important. Better if he also gets to shoot things. Knock cannonballs out of the air, save them both with his cleverness... or whatever.

John too. John and his steady wand arm. Sherlock knew it would be. Not that books pose much of a threat, of course. Still, they'll save each other, that's what they'll do. This is... metaphorical. Allegorical? Hardly matters, some narrative technique Sherlock doesn't give a toss about; point is, they're building something here. Sort of. At least in within the confines of Sherlock's head.

"Whatever you like; you're the captain."