Complex sentence: Chetwode believed that the lack of water would be easier to overcome than the Gaza fortifications and so a mammoth engineering and supply effort was undertaken to make a forward base in the vicinity of Beersheba from which infantry and mounted troops could stage an assault.
Split into simpler sentences: Chetwode believed that the lack of water would be easier to overcome than the Gaza fortifications. A mammoth engineering and supply effort was undertaken to establish a forward base in the vicinity of Beersheba, from which infantry and mounted troops could stage an assault.