E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Base of Operation,
in war. That is, a fortified or otherwise secure spot, where the magazines of all sorts can be formed, whence the army can derive stores, and upon which (in case of reverse) it can fall back. If a fleet, it is called a movable base; if a fortified or other immovable spot, it is called a fixed base. The line from such a base to the object aimed at is called the Line of Operation.