The I Marine Expeditionary Force ("I" pronounced "One") is a Marine Air Ground Task Force (MAGTF) of the United States Marine Corps primarily composed of the 1st Marine Division, 3rd Marine Aircraft Wing, and 1st Marine Logistics Group. It is based at Marine Corps Base Camp Pendleton.

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. It is presently commanded by Lieutenant General Christian F. Wortman. The deputy commander is Brigadier General Michael R. Nakonieczny.

Etymology

Pronunciation of the Roman numeral designator: As a Roman numeral the capital letter "I", representing one, is properly pronounced as "One". However, there are some who erroneously pronounce the number as either "First", or either intentionally, or unknowingly, pronounce it as "Eye", as in the letter "I".

The convention of using Roman numerals to designate a MEF, which is itself the Marine Corps equivalent organization to an Army corps, stems from the U.S. Army practice that began during the First World War, and continues today, of numbering corps (two or more divisions with supporting troops, and sometimes including separate brigades, regiments, groups, or battalions, all under a unified corps headquarters, usually commanded by a lieutenant general) with Roman numerals. Corps, themselves being the first-level sub-unit of a "field army", or a numbered, or named, army (e.g., First U.S. Army, or the Army of the Potomac).

During the First World War, the 4th Marine Brigade, as part of the U.S. Army 2nd Infantry Division, came under the U.S. Army I Corps, American Expeditionary Forces. With the expansion of the Marine Corps to six divisions and five air wings during the Second World War, the Marine Corps created two "Amphibious Corps", I Marine Amphibious Corps (later re-designated as III Amphibious Corps) and V Amphibious Corps, continuing the custom begun by the Army. Modern Marine Expeditionary Forces, or MEFs (for a time known as Marine Amphibious [italics added] Forces, or MABs) continue the U.S. Marine Corps legacy as corps-equivalent organizations designated by Roman numerals.

Mission

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.

Lineage

NATO Symbol
I
I
  • Activated on 8 November 1969 at Okinawa, Japan as the I Marine Expeditionary Force
  • Redesignated on 18 August 1970 as the I Marine Amphibious Force (I MAF)
  • Relocated in April 1971 to Camp Pendleton, California
  • Redesignated on 5 February 1988 as the "I Marine Expeditionary Force"

Organization

I Marine Expeditionary Force organization as of May 2026 (click to enlarge)

Units

Recent service

I Marine Expeditionary Force during the 2003 invasion of Iraq.

List of commanders

From 1969 through 1990 Commanding General, I MEF was normally concurrently assigned as Commanding General, 1st Marine Division and on occasion also Commanding General, Marine Corps Base Camp Pendleton.

Lt. Gen. Karsten S. Heckl, former commanding general, I Marine Expeditionary Force (MEF), passes the colors to Lt. Gen. George W. Smith Jr., signifying the change of command of I MEF during a formal ceremony on September 23, 2021.
No.CommanderTermRef
PortraitNameTook officeLeft officeTerm length
-Major General William K. Jones (1916–1998)Nov 1969April 1970180days-
-Major General Charles F. Widdecke (1919–1973)30 Apr 19711 Jul 197162days-
-Major General Ross T. Dwyer (1919–2001)1 Jul 197110 Aug 19721year, 40days-
-Major General James L. Day (1925–1998)1 Jul 198113 Aug 19821year, 43days-
-Major General Ernie Cheatham (1929–2014)13 Aug 198213 Jun 19852years, 304days-
-Major General Clyde D. Dean (1930–2001)13 Jun 198523 Apr 1986304days-
-Major General James J. McMonagle (1932–2024)14 Aug 198619 Jul 19881year, 340days-
-Major General John P. Monahan (1932–2023)20 Jul 19887 Aug 19902years, 18days-
-Lieutenant General Walter E. Boomer (born 1938)15 August 19906 September 19911year, 22days-
-Lieutenant General Robert B. Johnston (1937–2023)6 September 1991July 1993~1year, 298days-
-Lieutenant General George R. Christmas (born 1940)July 1993July 1994~1year, 0days-
-Lieutenant General Anthony Zinni (born 1943)July 1994October 1996~2years, 92days-
-Lieutenant General Carlton W. Fulford Jr. (born 1944)October 1996April 1998~1year, 182days-
-Lieutenant General Bruce B. Knutson Jr. (born 1946)April 19987 July 2000~2years, 97days-
-Lieutenant General Michael W. Hagee (born 1944)7 July 200018 November 20022years, 134days
-Lieutenant General James T. Conway (born 1947)18 November 200212 September 20041year, 299days-
-Lieutenant General John F. Sattler (born 1949)12 September 200414 August 20061year, 336days
-Lieutenant General James Mattis (born 1950)14 August 20065 November 20071year, 83days
-Lieutenant General Samuel T. Helland (born 1947/1948)5 November 200716 October 20092years, 348days
-Lieutenant General Joseph Dunford (born 1953)16 October 200919 October 20101year, 3days
-Lieutenant General Thomas D. Waldhauser (born 1955)19 October 201012 September 20121year, 329days
-Lieutenant General John A. Toolan (born 1954)12 September 201211 July 20141year, 302days
-Lieutenant General David H. Berger (born 1959)11 July 201427 July 20162years, 16days
-Lieutenant General Lewis A. Craparotta (born 1959)27 July 201630 July 20182years, 3days
-Lieutenant General Joseph Osterman (born 1959)30 July 201831 July 20202years, 1day
-Lieutenant General Karsten Heckl (born 1964)31 July 202023 September 20211year, 54days
-Lieutenant General George W. Smith Jr.23 September 202118 August 20231year, 329days
-Major General Bradford J. Gering Acting18 August 202316 February 2024182days
-Lieutenant General Michael S. Cederholm16 February 202421 August 20251year, 186days
-Lieutenant General Christian F. Wortman21 August 2025Incumbent1year, 13days-

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