During World War I, Jewish soldiers in all combatant armies collectively held dozens if not hundreds of Passover seders, ranging from the ad-hoc to the officially approved and planned. Adolf Fraenkel, an Orthodox German mathematician who later became the rector of Hebrew University, described one such ritual meal in his memoirs, as Ro Oranim writes:
In 1915, Fraenkel found himself serving as a medical orderly for the army, which included such responsibilities as transcribing autopsy reports from dictation and assisting in minor surgeries. During his two years of service in the field hospitals, Fraenkel was also authorized by the Bavarian Ministry of Cultural Affairs to serve as the Jewish chaplain for his fellow soldiers. While this position did not reduce the responsibilities of his day-to-day service, it did offer him a chance to stay connected to his religion and to assist others in maintaining their traditions as well.
In 1915, Fraenkel was stationed at the military hospital in the French city of Cambrai. . . . Fraenkel took his position [as chaplain] seriously, arranging for prayer services in the field and ensuring that soldiers could celebrate their holidays to the extent possible. At the end of March 1915, Fraenkel prepared . . . a list of the local soldiers who were interested in joining the seder, . . . set to take place on the 29th and 30th days of the month. . . .
A total of nine soldiers registered for both of the seders, including men serving as medics, logistics officers, combat engineers, and one serving in the newly formed German air force who did not specify which seder he planned to attend, perhaps because he knew there was a chance he would be called away at the last minute.
Read more on The Librarians: https://blog.nli.org.il/en/great_war_passover/