User blog comment:Answeration/The true enemy in AC3/@comment-94.0.109.198-20120611102753

Navel Combat is NOT DLC, They have already stated that Connor (I assume it will be only after he gains control of the ship) can hop onto his boat any time he likes... and explore the caribbean sea

Plus the demo also suggests he was chasing down a target, so it wouldn't be DLC.

All exclusive missions, (Well exclusive until DLC number 3) will not impact the story very much if at all, just as with the Vlad Mission