Which Assassin's Creed game introduced the series' first naval combat system?

Assassin's Creed III introduced the Assassin's Creed series' first naval combat system.

The game added naval missions in which the player commands the warship Aquila, engages enemy vessels, and navigates coastal waters. These sequences became a notable part of the game's design and established mechanics later expanded substantially in Assassin's Creed IV: Black Flag.

Assassin's Creed III was released in 2012 and is set during the American Revolution. Its main playable character is Connor, also known as Ratonhnhaké:ton, while the story also includes his father, Haytham Kenway. Black Flag is more strongly associated with naval gameplay because sailing is central to its open world, but Assassin's Creed III introduced the system to the main series first.