Complex sentence: Here, they faced the first gas attack in the entire war.The Battalion went "over the top" on one early morning with the rest of the fourth division, where the mustard gas, that the Germans used, killed many of the 50th's officers.
Split into simpler sentences: Here, they faced the first gas attack in the entire war. The battalion went "over the top" on one early morning with the rest of the fourth division, where the mustard gas, that the Germans used, killed many of the 50th's officers.