The United States Merchant Marine refers to either United States civilian mariners or to a fleet of U.S. civilian and federally owned merchant vessels. These fleets are managed by either the government or private sector, and 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 times of war, they can be an auxiliary to the United States Navy, and can be called upon to deliver military personnel and materiel for the military. Merchant Marine Officers may also be designated as Military Officers by the Department of Defense. This is commonly achieved by commissioning unlimited tonnage Merchant Marine Officers as Strategic Sealift Officers in the Naval Reserves.
Merchant mariners move cargo and passengers between nations and within the United States, and operate and maintain deep-sea merchant ships, tugboats, towboats, ferries, dredges, excursion vessels, charter boats and other waterborne craft on the oceans, the Great Lakes, rivers, canals, harbors, and other waterways.
As of 2006, the United States merchant fleet had 465 privately owned ships of 1,000 or more gross register tons. Nearly 800 American-owned ships are flagged in other nations.
The federal government maintains fleets of merchant ships via organizations such as Military Sealift Command and the National Defense Reserve Fleet, which is managed by the United States Maritime Administration. In 2004, the federal government employed approximately 5% of all American water transportation workers.
In the 19th and 20th centuries, various laws fundamentally changed the course of American merchant shipping. These laws put an end to common practices such as flogging and shanghaiing, and increased shipboard safety and living standards. The United States Merchant Marine is also governed by several international conventions to promote safety and prevent pollution.
P.L. 95–202, approved November 23, 1977, granted veteran status to Women Airforce Service Pilots and "any person in any other similarly situated group" with jurisdiction for determination given to the Secretary of Defense who delegated that determination to the Secretary of the Air Force. Although they suffered the greatest casualty rate of any service, merchant mariners who served in World War II were denied such recognition until 1988 when a federal court ordered it. The Court held that "the Secretary of the Air Force abused its discretion in denying active military service recognition to American merchant seamen who participated in World War II."