Complex sentence: The efforts of the partisans seem to vanish and their commitment and their abilities become meaningless, especially the trench mortars that already wounded Lt. Henry ("he knew that they would die as soon as a mortar came up").
Split into simpler sentences: The efforts of the partisans seem to vanish, their commitment and their abilities become meaningless., especially the trench mortars that already wounded Lt. Henry ("he knew that they would die as soon as a mortar came up").