Which Assassin's Creed game was the first to introduce naval ship combat as a major gameplay system?

Assassin's Creed III was the first Assassin's Creed game to introduce naval ship combat as a major gameplay system. Its optional naval missions let players command the Aquila and fight enemy vessels in the Atlantic Ocean.

The naval system was created for Assassin's Creed III's maritime sequences, which take place alongside the main story in the American Revolution. Players steer the ship, manage speed, use broadsides, and employ different weapons against sailing ships. These missions helped establish mechanics that later became central to the franchise.

Assassin's Creed IV: Black Flag expanded naval gameplay dramatically and made it a core part of the experience, which is why it is sometimes mistakenly credited with introducing the feature. Assassin's Creed III came first, while Black Flag refined and greatly enlarged it.