---
title: "What credentials must a mariner hold to serve in a position requiring a Merchant Mariner Credential or TWIC? Answer in under 100 words."
canonical: https://www.m-i-n-d.ai/minds/maritime/credentials-must-mariner-hold-serve-position-requiring-merchant-mariner
jurisdiction: "US Federal · 46 CFR"
last_verified: 2026-08-26
license: CC BY 4.0 — https://creativecommons.org/licenses/by/4.0/
attribution: "Source: MIND (m-i-n-d.ai)"
---

# What credentials must a mariner hold to serve in a position requiring a Merchant Mariner Credential or TWIC? Answer in under 100 words.

A mariner serving in a position requiring a TWIC or MMC must hold an active MMC issued by the Coast Guard, a valid TWIC issued by the Transportation Security Administration (unless exempt under § 10.203(b)(1)), and a current medical certificate. The MMC and medical certificate must be presented to the Master at employment or before signing Articles of Agreement.

## Details / How it works

Under 46 CFR 15.401, a person may not be employed or serve in a position requiring a TWIC or MMC unless they hold all required credentials authorizing service in that capacity. This includes an active MMC issued by the Coast Guard, a valid TWIC issued by the Transportation Security Administration (unless exempt under § 10.203(b)(1)), and a current medical certificate. The MMC and medical certificate must be presented to the Master of the vessel at the time of employment or before signing Articles of Agreement.

## Numbers & thresholds

| Credential | Validity period |
|------------|----------------|
| Medical certificate (STCW vessels, age ≥18) | 2 years |
| Medical certificate (STCW vessels, age <18) | 1 year |
| Medical certificate (all other mariners) | 5 years |

## Exceptions & edge cases

An individual holding an active MMC is exempt from the TWIC requirement under § 10.203(b)(1). Additionally, the MMC requirement for individuals below officer/staff officer grades on U.S.-flagged merchant vessels of 100 GRT or more does not apply to mariners on vessels navigating exclusively on rivers and lakes (except the Great Lakes), mariners below officer rank on certain non-self-propelled vessels, and personnel without safety or security duties on casino vessels.

## Sources

- [1] U.S. National Archives, Electronic Code of Federal Regulations — 46 CFR 15.401 — Employment and service within restrictions of credential · https://www.ecfr.gov/current/title-46/section-15.401 · as of 2026-08-26