Thunder on South Mountain covers the American Civil War battle at South Mountain fought over Turner's and Fox's Gaps, September 14, 1862. Following the discovery of Confederate Special Order No. 191, which outlined the disposition of General Robert E. Lee's entire army across the countryside, Union commander Gen. George McClellan moved to catch the Rebel Army while it was so dispersed. At South Mountain, the Federal First and Ninth Corps tangled with an assorted Confederate force under D.H. Hill, who fought the battle of his life. Could he hold the Yankees at bay and buy enough time for Lee to pull his scattered army back together? Thunder on South Mountain is a tactical, brigade-level simulation of low complexity with an emphasis on command and control. A unique "army posture" matrix determines the sequence of play each turn, and leader effectiveness is governed by a combination of momentum, luck, and resource management. Based on the Fire in Mississippi system, the game adds several new features such as long-range artillery fire and target disruption, line of sight, corps leaders, and variable reinforcement times. Thunder on South Mountain is of high DTP (Desktop Publishing) quality with an 11x17 color map, 140 two-sided, color counters (that must be mounted and cut apart), a rules booklet, and player charts and cards.