46 CFR 15.401: Credentials required for mariner employment and service
Last reviewed: October 14, 2026
This section sets credential rules for employing and serving in mariner positions. Individuals must hold the required TWIC and/or MMC and endorsements, a current medical certificate where an MMC is required, and must serve within any restrictions on the credential. It also says who below officer grades must hold an MMC and lists exceptions.
Applies toPersons who employ or engage individuals, and individuals who serve, in positions required by law or regulation to hold a TWIC and/or MMC.
What it says
A person may not employ or engage an individual, and an individual may not serve, in a position requiring a TWIC and/or MMC unless the individual holds all required credentials authorizing that service and serves within any restrictions on the credential.
46 CFR 15.401(a)“unless the individual holds all credentials required, as appropriate, authorizing service in the capacity in which the individual is engaged or employed, and the individual serves within any restrictions placed on the credential.”
An individual holding an active MMC issued by the Coast Guard must also hold a valid TWIC issued by the Transportation Security Administration, unless the individual is exempt under § 10.203(b)(1) of this subchapter.
46 CFR 15.401(a)“An individual holding an active MMC issued by the Coast Guard must also hold a valid TWIC issued by the Transportation Security Administration unless the individual is exempt under § 10.203(b)(1) of this subchapter.”
A person may not employ or engage an individual in a position required to hold an MMC unless the individual maintains a current medical certificate.
46 CFR 15.401(c)“A person may not employ or engage an individual in a position required to hold an MMC unless that individual maintains a current medical certificate.”
Medical certificates are issued for two years for individuals serving on vessels to which STCW applies, unless the mariner is under the age of 18, in which case the maximum is 1 year. The certificate may note a different period.
46 CFR 15.401(c)(1)“Two years for individuals serving on vessels to which STCW applies unless the mariner is under the age of 18, in which case the maximum period of validity will be 1 year.”
The MMC, along with a valid medical certificate, must be presented to the Master of the vessel at the time of employment or before signing Articles of Agreement.
46 CFR 15.401(d)“must be presented to the Master of the vessel at the time of employment or before signing Articles of Agreement.”
Each individual below the grades of officer and staff officer employed on a U.S.-flagged merchant vessel of 100 GRT or more must have a valid MMC issued by the Coast Guard, except for the cases listed in paragraphs (e)(1) through (e)(3).
46 CFR 15.401(e)“must possess a valid MMC issued by the Coast Guard, except as noted below:”
Every person employed on a vessel with dual tonnages must hold a credential authorizing service appropriate to the tonnage scheme under which the vessel is manned and operating.
46 CFR 15.401(f)“must hold a credential authorizing service appropriate to the tonnage scheme under which the vessel is manned and operating.”
Common questions
How long is a mariner medical certificate valid?
Unless otherwise noted on the certificate, it is five years for all mariners other than those serving on vessels to which STCW applies. For those on STCW vessels it is two years, or 1 year if the mariner is under the age of 18.
“Two years for individuals serving on vessels to which STCW applies unless the mariner is under the age of 18, in which case the maximum period of validity will be 1 year.”
Who must the MMC and medical certificate be presented to?
They must be presented to the Master of the vessel at the time of employment or before signing Articles of Agreement.
“must be presented to the Master of the vessel at the time of employment or before signing Articles of Agreement.”
Do casino vessel crew need an MMC?
Personnel not designated with any safety or security duties onboard casino vessels are excepted from the MMC requirement in paragraph (e).
“Personnel not designated with any safety or security duties onboard casino vessels.”
Does an MMC holder also need a TWIC?
Yes, an individual with an active Coast Guard MMC must also hold a valid TWIC, unless exempt under § 10.203(b)(1) of this subchapter.
“An individual holding an active MMC issued by the Coast Guard must also hold a valid TWIC issued by the Transportation Security Administration unless the individual is exempt under § 10.203(b)(1) of this subchapter.”
The text of 46 CFR 15.401
Electronic Code of Federal Regulations (eCFR), current as of April 16, 2026 · Read it on eCFR
Employment and service within restrictions of credential
(a) A person may not employ or engage an individual, and an individual may not serve, in a position in which an individual is required by law or regulation to hold a Transportation Worker Identification Credential (TWIC) and/or Merchant Mariner Credential (MMC), unless the individual holds all credentials required, as appropriate, authorizing service in the capacity in which the individual is engaged or employed, and the individual serves within any restrictions placed on the credential. An individual holding an active MMC issued by the Coast Guard must also hold a valid TWIC issued by the Transportation Security Administration unless the individual is exempt under § 10.203(b)(1) of this subchapter.
(b) A person may not employ or engage an individual, and an individual may not serve in a position in which it is required by law or regulation that the individual hold an MMC endorsed with a national endorsement, as well as a corresponding STCW endorsement for service outside the boundary line.
(c) A person may not employ or engage an individual in a position required to hold an MMC unless that individual maintains a current medical certificate. Medical certificates must be issued and will remain current for the following periods of time, unless otherwise noted on the certificate:
(1) Two years for individuals serving on vessels to which STCW applies unless the mariner is under the age of 18, in which case the maximum period of validity will be 1 year.
(2) Five years for all other mariners.
(d) Each individual referred to in paragraph (a) of this section must hold an MMC that serves as identification, with an appropriate endorsement for the position in which the seafarer serves, and the MMC, along with a valid medical certificate, must be presented to the Master of the vessel at the time of employment or before signing Articles of Agreement.
(e) Each individual below the grades of officer and staff officer employed on any U.S.-flagged merchant vessel of 100 GRT or more must possess a valid MMC issued by the Coast Guard, except as noted below:
(1) Mariners on vessels navigating exclusively on rivers and lakes, except the Great Lakes, as defined in § 10.107 of this subchapter.
(2) Mariners below the rank of officer employed on any non-self-propelled vessel, except seagoing barges and barges to which 46 U.S.C. chapter 37 applies.
(3) Personnel not designated with any safety or security duties onboard casino vessels.
(f) Every person employed on a vessel with dual tonnages (both domestic and international) must hold a credential authorizing service appropriate to the tonnage scheme under which the vessel is manned and operating.
Sections it refers to
The plain-English explanation on this page was written with AI from the regulation text above and checked automatically before publishing: every quote appears in the text, every number comes from it, and a second model confirmed each statement adds nothing the text doesn't say. Regulation text current as of April 16, 2026. The regulation text governs. RegKnot is not affiliated with the U.S. Coast Guard.