Private merchant ships often had cannons (those that didn't would be easy prey for pirates). I think in a duel between a merchant ship armed with 18th-century cannons and someone with an AK-47, the merchant ship would win.
Peace through superior firepower. Had to say that. I have a very nice friend who's a liberal at heart, and every time she tells me we should strive for peace, I tell her we are, through superior firepower.