The Coast Guard employs a three-tiered system of Maritime Security (MARSEC) Levels designed to easily communicate to the Coast Guard and its maritime industry partners pre-planned scalable responses for credible threats. If the Secretary of Homeland Security issues an NTAS Alert, the Commandant of the U.S. Coast Guard will adjust MARSEC Level, if appropriate, based on the commensurate risk, any maritime nexus, and/or Commandant consultation with the Secretary of Homeland Security.
MARSEC Levels are set to reflect the prevailing threat environment to the marine elements of the national transportation system, including ports, vessels, facilities, and critical assets and infrastructure located on or adjacent to waters subject to the jurisdiction of the U.S. MARSEC Levels apply to vessels, Coast Guard-regulated facilities inside the U.S., and to the Coast Guard.
MARSEC Level 1 means the level for which minimum appropriate security measures shall be maintained at all times.
MARSEC Level 2 means the level for which appropriate additional protective security measures shall be maintained for a period of time as a result of heightened risk of a transportation security incident.
MARSEC Level 3 means the level for which further specific protective security measures shall be maintained for a limited period of time when a transportation security incident is probable, imminent, or has occurred, although it may not be possible to identify the specific target.
MARSEC Level 1 generally applies in the absence of an NTAS Alert or when the Commandant determines that the Alert is not applicable to the Marine Transportation System. If an NTAS Alert is applicable, the Commandant will consider a MARSEC Level change for the maritime industry, Coast Guard, or both.