My recommendation is for you to go to the following website in the National Archives to get the answer to your question.
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Dear Ms. Lubeley,
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The Merchant Marine Personnel and Licensing Records dated prior to 1968 in the Records of the U.S. Coast Guard (Record Group 26) are in the custody of the National Archives at St. Louis (RL-SL). Please contact RL-SL via email at firstname.lastname@example.org. Include the name, date of birth, dates of service, "Z" number, and date of death, if known, in your request. The National Archives at St. Louis does not provide information for benefits or separation documents, such as DD-214s, for these records. To determine eligibility for a Certificate of Release or Discharge from Active Duty, DD Form 214, or a Report of Casualty, DD Form 1300, customers will be directed to to NMC’s website . RL-SL also will refer requests to the NMC on a customer's behalf.
Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request from RL-SL. We apologize for this inconvenience and appreciate your understanding and patience.
We hope this is helpful. Best of luck with your research!