Which Assassin's Creed game first centered its story on a pirate captain and naval exploration?

Assassin's Creed IV: Black Flag was the first Assassin's Creed game to center its story on a pirate captain and naval exploration. Released in 2013, it follows Edward Kenway, a Welsh privateer who becomes entangled in the Assassin–Templar conflict.

Edward commands the ship Jackdaw across the Caribbean Sea. Naval travel, ship upgrades, boarding actions, underwater exploration, and sea shanties are core parts of the game rather than occasional side activities. The historical setting includes Nassau, Havana, and Kingston during the Golden Age of Piracy.

Assassin's Creed III introduced substantial naval missions, so it is a frequent source of confusion. Black Flag expanded that idea into the central structure of the game and made maritime exploration its defining feature.