An instance of second-order Cyc collection, and a faceting collection on modern military organization. In military parlance, there is a tendency to describe units by their size, relative to the typical sizes of echelons. So a unit (of any echelon) might or might not be battalion-sized, brigade-sized, and so on. Each instance of echelon size is a collection of instances of modern military organization that all share a common size, typical of some particular echelon (c.f. military echelon). See also Military Unit Type Of Size Fn, which can be used to reify instances of this collection on the fly.