The Maritime Expeditionary Security Force (MESF) is a unit of the United States Navy within the organizational structure of the Navy Expeditionary Combat Command. The MESF stems from the Naval Coastal Warfare community which is transitioning to the MESF, Naval units affected range from mobile inshore undersea warfare units, inshore boat units, naval coastal warfare squadrons. The MESF's primary mission is force protection conducted through fleet support with operations around the world. Anti-terrorism and force protection missions include harbor and homeland defense, coastal surveillance, and special missions. Specialized units work together with MESF squadron staffs providing intelligence and communications. MESF units deploy worldwide to detect, deter, and defend an area, unit, or high-value asset. Recent locations include the United States, Panama, Korea, Saudi Arabia, Kuwait, Iraq, Afghanistan, Bahrain, United Arab Emirates, and Egypt.
Ratings range from Master-at-Arms to Boatswain's Mates, to Information Technology Specialists to Hospital Corpsmen. Preliminary units received training in small arms, crew-served weapons, and close quarters battle at places such as the Blackwater Training Center in Myock, North Carolina. Expeditionary Designated Marksman training conducted by the "in house" Special Missions Training Division of MESG-2 turns out shooters capable of sub MOA (minute of angle) accuracy.