Merchant Mariner Credential (MMC) Officer endorsements, commonly called the Captain Licenses, are issued a Master, Mate, or Operator endorsements with one of the following routes.
- An Oceans route has authority over all federally navigable Inland waters of the United States, the Great Lakes, and all ocean waters.
- A Near Coastal route has authority over all federally navigable Inland waters of the United States, the Great Lakes, and the near coastal ocean waters within 200 miles of the coastline.
- An Inland and Great Lakes route has authority over all federally navigable Inland waters of the United States, and the Great Lakes.
- An Inland route has authority over all federally navigable Inland waters of the United States.
- A Restricted route has authority over a single federally navigable Inland waterway of the United States and may only be issued for waterways that do not have any commercial vessel traffic.
The captain license that has the highest level of authority is Master. The Master is in charge of the entire vessel; any Mates or Engineers would report directly to the Master. There are several different categories of Master endorsements; Master (meaning inspected vessels and uninspected vessels except for towing vessels), Master of Fishing (meaning uninspected fishing industry vessels), and Master of Towing (meaning uninspected towing vessels). These endorsements are issued with tonnage limitations of 25, 50, 100, 150, 200, 500 1600, and Unlimited; tonnage limitations reflect the size of vessels the mariners sea service experience was on and the size of vessel the endorsement authority is extended to.
An endorsement as Mate is the next lower level of authority for a MMC officer endorsements. This endorsement authorizes the authority to be the officer in charge of a navigational watch and is issued in the same categories and with the same tonnage limitations as the Master endorsement. Any mariner holding an MMC endorsement as Mate may serve as the Operator of Uninspected Passenger Vessel, and any Mate endorsement of 500 tons or more may serve as Master 100 tons.
The Operator of Uninspected Passenger Vessel is the smallest captain endorsement issued. This endorsement has authority over uninspected passenger vessels less than 100 tons carrying 6 or fewer passengers for hire (AKA the 6-pack license).