Complex sentence: The Battle of Tabsor began with an intense creeping bombardment, during which three infantry divisions of the XXI Corps attacked the Tabsor defences; the only continuous trench-and-redoubt system on the Ottoman front line.
Split into simpler sentences: The Battle of Tabsor began with an intense creeping bombardment, during which three divisions of the XXI Corps. They attacked the Tabsor defences; the only continuous trench-and-redoubt system on the Ottoman front line.