Terrible Swift Sword: The Three Days of Gettysburg (often abbreviated as TSS) is a classic grand tactical, regimental level board wargame depicting the Battle of Gettysburg of the American Civil War. It was published by Simulations Publications, Inc. (SPI) in 1976, and remains one of the largest Civil War board games ever produced. TSS won the 1976 Charles S. Roberts Award for Best Tactical Game. It was considered groundbreaking among wargaming hobbyists.
Gameplay takes place over a large series of turns, where each daylight game turn represents 20 minutes of simulated battle action; each night turn simulates 1 hour. Game scenarios include The First Day (29 game turns), The Second Day (40 turns), Little Round Top (6 turns), The Third Day (Pickett's Charge) (21 turns), and the Grand Battle Game: The Three Days of Gettysburg (149 turns, approximated at 50 hours of playing time). The game inventory includes over 2,000 counters, one 32-page rules booklet, one historical situation briefing booklet, three unmounted 22" x 32" paper game maps depicting the battlefield at 120 yards per hex, and one six-sided die. Players alternate taking turns, depending upon the scenario. The time required to play is one of the longest of all SPI games, often taking longer than it took to fight the battle in real life, and the game is sometimes jocularly referred to as "Terrible Slow Sword" in consequence.
Game designer Richard Berg collaborated on a series of other Civil War boardgames based upon the TSS game mechanics and system, including the Great Battles of the Civil War series. An add-on game, Rebel Sabers, expanded TSS to include the East Cavalry Field fight. A second edition of Terrible Swift Sword was published in 1986 by TSR, Inc., and Berg later produced a similar game, Three Days of Gettysburg, for GMT Games in 1995. Terrible Swift Sword inspired the popular miniature wargaming scenario book series, Enduring Valor: Gettysburg in Miniature, which loosely adapted some of the basic regimental scenario concepts.
The name "Terrible Swift Sword" is taken from the Civil War era song "Battle Hymn of the Republic," which has in its opening lines "He hath loosed the fateful lightning of his terrible swift sword."