Which unit size is primarily represented by the Marine Expeditionary Force (MEF)?

The Marine Expeditionary Force (MEF) represents a division-sized unit primarily due to its structure and operational capabilities. A MEF typically consists of a command element, a ground combat element that is usually a division, an aviation combat element, and a logistics combat element. This composition allows the MEF to project decisive combat power and sustain a range of military operations on a large scale.

Within the Marine Corps structure, a division consists of several regiments (which are themselves made up of battalions). Thus, the MEF's organization as a large integrated force tasked with amphibious operations and sustained ground combat aligns closely with the characteristics of a division, making it the correct answer in this context.

The other unit types do not represent the scale and operational functionality of a MEF. A battalion is smaller than a MEF, typically comprising around 500 to 1,000 Marines. A regiment is larger than a battalion but smaller than a division in the overall command structure. The corps is synonymous with a grouping of multiple divisions, leading to a size that exceeds the MEF's organization.