Which Assassin's Creed game introduced the series' modern naval warfare as a major feature?

Assassin's Creed III introduced naval warfare as a major feature of the Assassin's Creed series.

The game includes missions in which Connor Kenway commands the ship Aquila, combining sailing, broadside cannon fire, maneuvering, and encounters with enemy vessels. These sequences were substantial enough to become a recognized part of the game's design rather than a minor travel mechanic.

Assassin's Creed III is set during the American Revolution and includes coastal areas, rivers, and frontier environments. Its naval missions helped demonstrate how the series could expand beyond city-based parkour and assassination activities.

Assassin's Creed IV: Black Flag greatly expanded the idea into a central open-world system, which is why it is sometimes mistakenly credited with introducing naval gameplay. Black Flag popularized and deepened the feature, but Assassin's Creed III came first in the main series.