The National Vessel Movement Center, commonly abbreviated NVMC, is a military subdivision of the United States Coast Guard, assigned to record and monitor arrivals of ships within United States ports. Its purpose is to prevent terrorist attack. The NVMC commenced operations on October 15, 2001, relieving the United States Department of Transportation of this responsibility. 361 U.S. ports are on watch, with 55 (15%) indicated as militarily or economically critical. All ship classifications are monitored. Information recorded includes: