Karl d'Elsa was in command of XII (1st Royal Saxon) Corps at the outset of World War I, part of the predominantly Saxon 3rd Army on the right wing of the forces that invaded France as part of the Schlieffen Plan offensive in August 1914. He led the XII Corps at the First Battle of the Marne and First Battle of the Aisne. On 17 April 1916 he was given command of "Armee-Abteilung A" on the Western Front but was placed on inactive reserve status on 4 January 1917.