A licensed mariner is a person who holds a license issued by one or more countries to hold senior positions aboard ships, boats, and similar vessels. The United States Coast Guard grants licenses to members of the United States Merchant Marine in five categories: deck officers, engineers, staff officers, radio officers, and pilots. The United States Coast Guard has replaced paper licenses with the Merchant Mariners Credential which is a combination of the former Merchant Marine Officers license and Merchant Mariners Document in a small book that looks similar to a passport.