>>/49711/
It's purely operational.
At lowest level the player designates units participating in battles, but the battles itself are just calculated (since they are on tactical level)
At highest level the player gets the units, reinforcements just appear and has no say in what units and how much he gets (since the "production" of units is the task of strategy).
In between the player directs the units, moves them, arranges them, on a theater or operation.
There is also a reason why operations are named as Operation Blahblah (eg. Operation Barbarossa, Op. Avalanche, Op. Desert Storm, etc.). For they are on operation level.