The Expeditionary Strike Group, or ESG, is a concept introduced in the U.S. military in the early 1990s, based on the Naval Expeditionary Task Force. The U.S. Navy fields 12 Expeditionary Strike Groups and 10 Carrier Strike Groups, in addition to surface action groups. ESGs allow US naval fleets to provide highly movable and self-sustaining forces for missions in various parts of the globe.
An Expeditionary Strike Force (ESF) integrates the CSG and ESG with the sea-basing functions provided by the Maritime Prepositioning Force (future) to provide an even more potent capability.
The Marine Corps and the Navy are conducting a series of experiments to explore the ESG and ESF concepts. As noted, the ESG concept combines the capabilities of surface action groups, submarines, and maritime patrol aircraft with those of Amphibious Ready Groups and Marine Expeditionary Units (Special Operations Capable) to provide greater combat capabilities to theater combatant commanders.