What department does the merchant marine belong to?

The merchant marine primarily falls under the Department of Transportation's Maritime Administration. This department oversees the merchant marine's functions, including the regulation of U.S. merchant vessels, support for the maintenance and training of mariners, and the promotion of U.S. positions for maritime activities.

The Maritime Administration not only ensures that the United States maintains an adequate fleet for commerce and defense purposes but also provides training programs for civilian mariners. This administration plays a crucial role in supporting the maritime industry, which is essential for international trade and national security.

While other departments like the Department of Defense or Department of Homeland Security may interact with or oversee certain aspects of maritime security or operational functions, the direct governance and regulation of the merchant marine fall squarely within the purview of the Department of Transportation.