The Blitzkrieg Legend simulates Case Yellow, the German offensive in May of 1940 that shocked the world. In less than a month's time it made quick work of Belgium and Holland, shattered the armies of France, and pushed the British Expeditionary Force (BEF) into the sea at Dunkirk. This twelfth game in theOperational Combat Series (OCS) departs from its established norms in using a ground scale of 3 miles per hex and a time scale of two-day turns, and as such is similar to Sicily. The chosen scale lets this lightning campaign unfold a bit more slowly, and gives the densely-packed armies more room to maneuver.

Case Yellow achieved the largest pocket ever to be created in the war, with the largest number of captured soldiers as well. This result is sometimes looked upon by gamers and historians alike as a foregone conclusion, but Manstein's daring strike through the Ardennes was a gamble that might easily have gone awry. Hindsight suggests the fighting could have gone much differently.

A range of historical problems confront the player directing the Allies in this game. His French, Belgian, Dutch, and BEF combat units have not yet mastered the faster pace of action in WWII, and therefore are slow and don't fight at full Action Rating when in Move Mode. The Allies are also forced to adopt the historical Dyle Plan (when not playing the what-if version of the campaign), which leaves the French with inadequate reserves behind the Ardennes and too many of their best forces committed to shielding Antwerp and Brussels. Because history tells us the headlong rush into Belgium was primary cause of the quick Allied defeat, an If I Was in Charge... version of the campaign is presented to allow both sides to explore some different initial deployments.