• The MMC and the TWIC serve two separate purposes for a mariner. The MMC serves as an individual’s qualification document, certificate of identification and certificate of service. The TWIC is an identification credential indicating that an individual does not pose a terrorism threat. When a Mariner serves on a vessel requiring a vessel security plan, he/she is required to have been issued a TWIC. TWIC is issued after the completion of a security threat assessment. MMC is issued after an applicant demonstrates he/she is qualified as to age, character, habits of life, experience, professional qualifications, physical fitness and citizenship.