Imagine being a Jewish soldier in the Union Army during the Civil War, in what would later become West Virginia where no one knew how to celebrate Passover. There were 21 Jewish soldiers in the 23rd Ohio Volunteer Infantry Regiment under the command of future president Rutherford B. Hayes in 1862. Most were young men who had celebrated, but had never organized a Passover Seder before. Private Joseph A. Joel obtained permission for the soldiers to take a day off for the Seder, and it was granted.
The men had to enlist help from their provisions supplier and the local residents to get what they needed for the feast. Cider was a substitute for wine, and whatever they substituted for the usual horseradish and parsley as the bitter herb was so bitter that it caused the men to drink all the cider and the Seder got quite lively, or even rowdy. Joel published an account of that Seder in 1866 in the Jewish Messenger. While it wasn't the only Passover celebration on the battlefield, it was the one best documented for posterity, and you can read about it at Smithsonian.
(Image source: Rutherford B. Hayes Presidential Library and Museum)