Complex sentence: During the bombing, the prisoners of war and German guards hide in a deep cellar, allowing them to be among the few survivors of the firestorm between 13 and 15 February 1945.
Split into simpler sentences: During the bombing, the prisoners of war and German guards hide in a deep cellar. Because of their hiding place, they are some of the few survivors of the firestorm caused by Allied bombing between 13 and 15 February 1945.