Stern served in World War I doing meteorological work on the Russian front while still continuing his studies and in 1915 received his Habilitation at the University of Frankfurt.
Stern terlibat dalam Perang Dunia I melakukan pekerjaan meteorologinya pada barisan Rusia ketika ia masih menjalani studinya dan pada tahun 1915 ia menerima habilitasi-nya di Universitas Frankfurt.