Explanation: GMDSS (Global Maritime Distress and Safety System) regulations for U.S.-flag vessels are found in **47 CFR Part 80**. The Code of Federal Regulations (CFR) contains the general and permanent rules published by federal agencies. Title 47 specifically covers "Telecommunication," and Part 80 details "Stations in the Maritime Services," encompassing all U.S. domestic and international maritime radio communications, including GMDSS requirements set forth by the FCC. Option A, CCIR #476, refers to an international recommendation concerning Digital Selective Calling (DSC) standards, not the regulatory location for U.S. federal law. Option C, "FCC Part 83," is not a valid part number for maritime radio regulations; Part 80 is the correct section. Option D is incorrect because while the U.S. Coast Guard enforces many maritime regulations, the primary federal rules for radio communication, including GMDSS, are established and published by the FCC under 47 CFR.