In World War I the battlefields of the K.u.k. Rifle Regiment No. 1 were in 1914 in Galicia in the first Battle of Lemberg, from 1915 until the war ended at the Battles of the Isonzo in the sector Carnic Alps from Tarvis to Predil Pass. Bregant Eugen 1915 was involved in several combat missions, including the Oregone pass, the storming of Monte Peralba and the Hohen Trieb. From 1916 until the war's end, he was commander of a machine-gun battalion (LIB No. 157), 1917 section commander of the height position Zollner, participating in several Battles of the Isonzo and then being used at various focal points of the front of Piave to Stelvio. On 4 November 1918 Bregant with the whole LIB No. 157 went along in Italian POWs Community as a result of a 36 hours too early announced armistice in Ponte di Ark in South Tyrol by the Austrian Army High Command (AOK), from which he was released on 4 August 1919.