The United States Merchant Marine is the fleet of U.S. civilian-owned merchant vessels, 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 peacetime. In time of war, the Merchant Marine is capable of being an auxiliary to the Navy, and can be called upon to deliver military personnel and materiel for the military. The Merchant Marine, however, does not have a role in combat, although a merchant mariner has a responsibility to protect cargo carried aboard his ship.