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 an army 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.
While there were a significant number of EAC in World War II, 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
Even in World War II, 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.