(a) The minimum service required to qualify an applicant for an endorsement as Master of Great Lakes and inland self-propelled vessels of less than 500 GRT is—

(1) Three years of total service on vessels. One year of the required service must have been as a Master, Mate, or equivalent position on vessels of 50 GRT or more while holding an MMC endorsement as Master, Mate, or OUPV.

(2) [Reserved]

(b) An applicant holding an MMC endorsement as Master of ocean, near-coastal, or Great Lakes and inland towing vessels is eligible for this endorsement after 6 months of service as Master of Towing Vessels and completion of a limited examination. This requires 3 1/2 years of service. Two years of this service must have been served while holding an MMC endorsement as Master or Mate (Pilot) of Towing Vessels, or Mate.