[1] On 1 October 1885 he entered as a second-lieutenant at the School of Artillery and Engineering Application (French: École d'application de l'artillerie et du génie) in Versailles.
[2] On 28 October 1915, he was awarded with the Croix de guerre for his "talent of organization, his masterful manner, and his activity which are all beyond praise, which permitted him to obtain from all his subordinates, by his personal energy and example, the maximum results"[4] which he had displayed during an artillery charge in September.
[2] When Geismar finally retired in January 1923, he became increasingly active in the Zionist movement, assisting the development of Keren Hayesod (Reconstruction Fund), with André Spire.
He participated and was a member of the steering committee for France-Palestine [fr], a Zionist advocacy group founded in 1926 by Joseph Paul-Boncour et Justin Godart.
[5] His fellow members included Édouard Herriot, Paul Painlevé, Jules Cambon, Aristide Briand, Raymond Poincaré, Alexandre Barthou, and Gaston Doumergue.
In 1928, he accepted the presidency of the Éclaireuses et éclaireurs israélites de France (EEIF), saying he was "training the young recruits of the Jewish people.
[5] He had two notable nephews: Léon Geismar, governor of French West Africa, and Max Hymans, CEO of Air France.