Explanation: Serving as a GMDSS (Global Maritime Distress and Safety System) operator requires specialized knowledge of international distress and safety communication procedures and equipment. The **GMDSS Radio Operator’s License** (GROL) is specifically issued by the FCC to certify an individual's proficiency in operating GMDSS installations on vessels, in accordance with international conventions (like SOLAS) and FCC regulations. The General Radiotelephone Operator’s License covers broad commercial radio operation but doesn't specifically address GMDSS protocols. A Marine Radio Operator’s Permit is a basic license for general maritime radio use, not GMDSS-specific operations. The GMDSS Radio Maintainer’s License certifies competence in repairing and maintaining GMDSS equipment, not primarily in its operational use for distress and safety communications.