 In 1775 the Continental Congress and the various colonies issued Letters of Marque to privately owned, armed merchant ships known as privateers, which were outfitted as warships to prey on enemy merchant ships.They interrupted the British supply chain all along the eastern seaboard of the United States and across the Atlantic Ocean and the Merchant Marine's role in war began.This predates both the United States Coast Guard (1790) and the United States Navy (1797).