If you hold a USCG license, an endorsement is required to operate a Towing Vessels ( NAVIC 3-16 ) states that a mariner may operate a towing vessel if, on or after 5/21/2006, and after any license transaction following any license upgrade or renewal, an officer operating towing vessels must hold any of the following licenses or endorsements:
Master of Towing Vessels.
Master of inspected self-propelled vessels greater than 200 GRT with a completed TOAR.
Mate (pilot) of towing vessel.
Mate of inspected self-propelled vessels greater than 200 GRT with a completed TOAR (limited to serving in the capacity of mate of towing).
Apprentice mate (steersman) under the direct supervision of a licensed officer. see visual flow chart.