What is the Merchant Marine?
The Merchant Marine is the fleet of ships which carries imports and exports during peacetime and becomes a naval auxiliary during wartime to deliver troops and war materiel. According to the Merchant Marine Act of 1936: "It is necessary for the national defense... that the United States shall have a merchant marine of the best equipped and most suitable types of vessels sufficient to carry the greater portion of its commerce and serve as a naval or military auxiliary in time of war or national emergency..." During World War II the fleet was in effect nationalized, that is, the U.S. Government controlled the cargo and the destinations, contracted with private companies to operate the ships, put guns and Navy personnel (Armed Guard) on board. The Government trained the men to operate the ships and assist in manning the guns through the U.S. Maritime Service

U.S. Maritime Service or U.S. Merchant Marine?
The United States Maritime Service was by law the official training organization for the U.S. Merchant Marine. It trained men for the U.S. Merchant Marine and U.S. Army Transport Service to transport supplies and personnel in the largest fleet of freighters, tankers, and transports in history to bases all over the world for U.S. and Allied forces. Men at the fronts depended on this important service for bombs, gasoline, shells, ammunition, food, guns, vehicles, planes, medicine, and other materials for warfare. When training ended the person was "released from active duty" in the Maritime Service and went to sea in the Merchant Marine. Today the Maritime Service exists only in the Maritime Academies.