During the Second World War, several Eastern European nations fielded flotillas of river monitors - armored, shallow-draft warships that operated on the great rivers. These gunboats (anything on a river is a “boat” no matter its size) were designed to provide artillery support, engage enemy troops and if necessary, to fight other river monitors.
River Battleships introduces these armored warships to Panzer Grenadier. These are the actual river warships that served Poland, Czechoslovakia, Romania, Germany, Yugoslavia, Croatia, Austria and the Soviet Union. There are 45 river monitor pieces (the same size as the ship pieces in our naval games), 32 slightly smaller river gunboat pieces, 50 special markers for the river craft and 64 standard Panzer Grenadier sized pieces with troops, weapons and leaders.
River Battleships is a complete game, with two 11x17-inch maps showing the beautiful blue Danube (or Dnepr, or Pripyet) in its full watery glory, a full set of Panzer Grenadier series game rules and charts, special rules for riverine combat, and sixteen new scenarios featuring river monitor action (plus one introductory scenario with just ground units).
-description from publisher's website