46 C.F.R. § 11.404
(a) The minimum service required to qualify an applicant for an endorsement as Master of ocean or near-coastal self-propelled vessels of unlimited tonnage is—
(2) While holding an MMC endorsement as Chief Mate of ocean self-propelled vessels of unlimited tonnage, 12 months of service on deck as follows:
(b) An individual holding an endorsement as Master of Great Lakes and inland, self-propelled vessels of unlimited tonnage, or Master of inland, self-propelled vessels of unlimited tonnage, may obtain an endorsement as Master of oceans or near-coastal self-propelled vessels of unlimited tonnage by providing evidence of sea service of not less than 24 months under the authority of the credential and by completing the prescribed examination in subpart I of this part. Service will be credited as follows:
[USCG-2004-17914, 78 FR 77909, Dec. 24, 2013, as amended by USCG-2021-0097, 89 FR 93079, Nov. 25, 2024; USCG-2021-0834, 89 FR 102334, Dec. 17, 2024]