Admitted to the Order in Oct. 1891, he was disappointed in his desire for a mission to India by the sudden onset of a serious illness, tuberculosis. Ordained priest in 1898, his precarious health prevented him from exercising ministry. He therefore devoted himself to historical studies and became an active collaborator of the Annales franciscaines and the Études franciscaines.
A discerning reader of sources and gifted with great acumen in archival research, his profiles of members of the Order, while delineating on the basis of exhaustive documentation the outward events of his subjects’ lives, never lack appropriate contextualization and fine psychological sensitivity. Among his writings, particular mention should be made of: Mémoires et lettres du p. Timothée de la Flèche sur les affaires ecclésiastiques de son temps (1907), accompanied by an introduction by U. and of great interest for the history of Jansenism; Leçons d'histoire franciscaine (1918), in which he condensed the fruit of his historiographical activity; Les Frères Mineurs Capucins de Reims, published in the Travaux de l'Académie de Reims of 1923 (vol. CXXXVII, pp. 75-235). During the First World War U. served in a hospital.