A Marine Expeditionary Unit would be made up of numerous MOS's.

Yes.

The Marine Expeditionary Brigade is smaller than the Marine Expeditionary Force, but larger than the Marine Expeditionary Unit. It is considered the "middle-weight" crisis response force of choice in the European and Southern Command Area of Operations. It is able to operate independently, as a service component, or to lead a Joint Task Force.

Command Element (CE), Ground Combat Element (GCE), Aviation Combat Element (ACE), Combat Service Support Element (CSSE)

III Marine Expeditionary Force was created in 1942.