"Shipments come faster."—In-game description
Merchant Marine is a Consulate technology in Age of Empires III: The Asian Dynasties that can be researched by the Japanese if they choose the Spanish as their ally once the Colonial Age is reached. Once researched, it reduces the time it takes for Home City shipments to arrive by 50%, essentially making them arrive at double speed.
Merchant Marine synergizes well with the Good Faith Agreements Home City Card which allows Consulate technologies to be researched twice as fast with a 40% discount.