A gold oak leaf with the initials “MSC” in gold letters on a black background is the insignia for the Lieutenant Commander grade in the Military Sealift Command. But the bulk of the Military Sealift Command personnel are Civil Mariner, and therefore are given different job titles to distinguish them from members of the Armed Forces. These job titles can vary based upon level of responsibility and the Department in which one is working.
A Lieutenant Commander in the Logistics Department, for example, is a Supply Officer, and has just one lower-ranked officer (Junior Supply Officer) under his or her command. And Lieutenant Commanders are the only Officers in the Purser and Medical Departments.
Each Department has an associated emblem. A vertical fouled anchor indicates Deck Officers; a propeller is worn by Engine Officers; a caduceus by Medical Offices; and so forth.
The Military Sealift Command was established in 1970 from the Military Sea Transportation Service.