Echelons above corps
Echelons above corps (EAC), in US and NATO practice, refer to higher headquarters, of purpose-built organization, which involve a greater number of troops than would be in a corps. They may be standing organizations with a regional responsibility, or may be established for a particular operational purpose. While EAC most commonly refer to ground combat forces, they may refer to joint commands. They may also be administrative headquarters with responsibility for preparing combat forces.
The role of the corps is changing. Traditionally, it was the highest-level tactical headquarters. Changes in military technology allow smaller tactical organizations, perhaps built on a division as the headquarters unit. Nevertheless, the idea of units that augment the highest tactical headquarters, and the additional adminiatrative and support units that comprise the organization above that headquarters, remains valid.
Echelons above division (EAD) is coming into more common use, since, in conflicts such as Iraq and Afghanistan, the senior operational headquarters may be a corps, or, during the active 2003 invasion, two corps with an interim coordinating headquarters.
While there were a significant number of EAC in WWII, with increasing power of smaller organizations, it may not be required to have a ground force of the size of:
- Field army, made up of two or more corps plus units under the direct control of the army commander
- Army group, composed of two or more field armies plus units subordinated to the army group commander
- Theater, composed of all land, sea, and air forces in a geographic area; the U.S. equivalent today is a Unified Combatant Command
Even in WWII, while the Western Allies used these terms, they were not universal. A Soviet army was roughly equivalent to a US or Commonwealth Corps, with a Front roughly equivalent to an Army Group. Japanese armies were also equivalent to US or Commonwealth Corps, an Area Army to a western Field Army, and a General Army to a Theater. US forces' highest levels are Unified Combatant Commands, roughly equivalent to a Theater. There are, however, "sub-unified commands", headed by four-star officers. Multi-National Force-Iraq (MNF-I) is a level of command comparable to a reinforced Field Army, composed of a Multinational Corps built on a U.S. Corps headquarters, plus several multinational divisions and other attached troops.
Besides MNF-I, other unusual four-star commands include the International Security Assistance Force (ISAF) in Afghanistan. In the Republic of Korea, a U.S. general hs the combined roles of United Nations Commander, commander of United States Forces Korea, and Eighth United States Army.