From the Avalanche Press website: The First Great War ended in December 1916 with Wilson’s Peace, a negotiated settlement that left all parties vaguely dissatisfied (except those no longer called on to die by the millions). The Second Great War erupted in August 1940, with Serbian, Russian, French and Italian armies attacking the Central Powers in a naked grab for territory and power. Armies and fleets were not the only forces the aggressors deployed. Along the broad Danube River, the Austrian flotilla fought to keep their Serbian enemies from pushing upstream into the heart of the Monarchy. The armored riverine warships, known as monitors, featured heavy guns and thick armor, in effect small battleships maximized for the river environment. But Serbia had built its own fleet of river vessels, as had their ally, Romania. River Fleets introduces these armored warships to Panzer Grenadier. It’s part of our Second Great War setting. There are 68 new playing pieces: 20 double-sized river monitors, and 48 standard-sized ones for smaller craft plus troops and leaders. There are also two new 11x17-inch maps showing the beautiful blue Danube in its full watery glory. Plus you get a set of 10 scenarios to use them (that’s as many as some publishers will give you in what they call a “complete” boxed game). River Fleets is a pretty-much self-contained Panzer Grenadier supplement. You'll need a rulebook, charts and markers from any Panzer Grenadier game.