Gerhard Besier The Great War and the Religion in comparative Perspective. Why 1914 the Christian war culture prevailed over religiously motivated pacifism. http://www.unifr.ch/szrkg/assets/files/leseproben/2014/besier_2014.pdf (German text with Google translate option).
How the Bible was used by both sides - a new inverstigation:
https://www.cam.ac.uk/research/news/a-conflict-of-biblical-proportions-how-the-bible-was-used-to-turn-the-first-world-war-into-a-holy
For a balanced overview of the attitudes of both British and German Biblical scholars during WW1: Andrew Mein, Nathan MacDonald & Mathew A Collins (eds) The First World War and the Mobilisation of Biblical Scholarship (2018) https://books.google.co.uk/books?id=-b6EDwAAQBAJ&printsec=frontcover&dq=von+harnack+and+WW1&hl=en&sa=X&ved=0ahUKEwjQofOEsY7iAhV8UBUIHR7LA78Q6AEIKjAA#v=onepage&q&f=false