United States Coast Guard Port Security Units are deployable specialized units organized for sustained force protection operations. They can deploy within 96 hours and establish operations within 24 hours of arrival. PSUs conduct OCONUS port security in support of requesting regional Combatant commander. They provide Anti-Terrorism and Force Protection missions which include harbor and port defense, Humanitarian aid, coastal surveillance, and special missions. PSUs usually operate in U.S. territorial waters under the direction of the Coast Guard’s command, but can quickly be called upon the Department of Defense request.

PSUs often operate and integrate with other NECC elements, such as Maritime Expeditionary Security Squadrons (MSRONs) within a Maritime Expeditionary Security Group. This makes PSU’s unique as they are the only Coast Guard unit supports and can be quickly requested and by the Department of Defense control. Providing port/waterside protection to key assets (e.g. pier areas, high-value vessels, harbor entrances) at the termination/origination point of the Sea Lines of Communications (SLOCs).

PSU’s originally were part of the Coast Guard's Deployable Operations Group (DOG) until the DOG was decommissioned; PSUs are now a part of the reorganized Deployable Specialized Forces.