Artillery battery
The plot revolves around a Union Army regiment and an artillery battery from the American Civil War which get transported to an alien world. The 35th Maine Infantry regiment and the 44th New York Light Artillery battery are being transported by ship from Virginia late in the war when they encounter a mysterious electrical storm and end up on a distant planet. The region they are in is populated by descendants of medieval Russians (or "Rus") who still live a feudal existence at a medieval level of technology. They learn from their new hosts that there are various civilizations on this world made up of the descendants of people from various eras of Earth history.