I Marine Expeditionary Force is the largest of the three MEFs in the Fleet Marine Force and is often referred to as the "Warfighting MEF" for its consistent involvement and contributions in major armed conflicts.
Among U.S. Marines, I MEF is pronounced as "one mef". Other pronunciations, such as "eye mef" and "first mef", are categorically viewed as incorrect and improper, with the latter being mistakenly used often.
When directed, I MEF deploys and is employed as a Marine Air Ground Task Force (MAGTF) in support of Combatant Commander (COCOM) requirements for contingency response or Major Theater War; with appropriate augmentation, serves as the core element of a Joint Task Force (JTF); prepares and deploys combat ready MAGTF’s to support COCOM presence and crisis response; and supports service and COCOM initiatives as required.