Op Art is a set of rules for operational level games on the Eastern Front of WWII. The author writes:
Operational Art is the term first coined by the Russians to describe the level oc fomat that falls between the tactics used on the battlefield and the strategic direction of a war. The basic units of manoeuvre are division sized formations and the decision making level is that of army commander.
The rules have been designed so that players can recreate battles fought at this level; as a result a degree of abstraction has been included in the mechanisms used and especially in the way in which combat is resolved.