What does the merchant marine do?
Staffie gave you a good answer, but you might want to take a look at this article, too: http://en.wikipedia.org/wiki/Merchant_marine It explains that saying “the merchant marine” is a way of referring to the merchant marine fleet — that is, all ships at sea which are not military ships and not pleasure boats, but rather the boats and ships which transport products for sale across the oceans, the way trains do on land.
Merchant marines have a system of ranks and specialties which closely correlates to that of the military. Some merchant marines specialize in a particular field, such as navigation, communications, or heavy equipment operations. Others attend a merchant marine academy to begin careers as officers. Most merchant marines intend to remain in the merchant marine for the duration of their careers, and many companies provide benefits and incentives to encourage their staff to continue serving. Most governments recognize the importance of the merchant marines to the economy and safety of the nation, and therefore supervise a Merchant Marine Academy. In the United States, the Merchant Marine Academy has been run by the government since 1943. Graduates of the academy have taken part in conflicts such as Vietnam and the Gulf War, in addition to serving as merchant marines on their home ships.
