According to lasdontrailofhonor.com:
The Merchant Marines monument is the first to present itself on this trail, and recognizes our Nation’s oldest naval division. Its creation dates back to the beginning of the revolution. Originally used by private trading companies, merchant marines were quickly recruited by the continental army after a group of Merchant Marines used a small sloop to defeat a large British ship called the HMS Margaretta. Since then, the Merchant Marines have served in every American conflict, bringing supplies and arms to our troops overseas and defending those valuable cargoes from the beginning to the end of their voyages. Recently they have served on transport ships for our troops in Iraq and defending supply lines headed for our ground troops from dangerous opposition. Their bravery at sea shows the true strength of our naval fleets, and they continue to be an invaluable asset to our military.