This closure appears to have been definitive. During the war, Mailhat served as ‘’Officier de l’administration de 3e classe territorial’’ in the Service des fabrications de l'aviation (military aircraft manufacturing). For his contribution to the war effort, he received the Légion d’Honneur in 1918. Mailhat died on 22 April 1923 at his home at 13, rue Boileau in Montrouge (Seine).