The United States Merchant Marine refers to the fleet of U.S. civilian-owned merchant ships, operated by either the government or the private sector, that engage in commerce or transportation of goods and services in and out of the navigable waters of the United States. The Merchant Marine is responsible for transporting cargo and passengers during peace time. In time of war, the Merchant Marine is an auxiliary to the Navy, and can be called upon to deliver troops and supplies for the military.