Complex sentence: After three days the trenches were practically obliterated, forcing the men to occupy the shell holes in front of them instead, an by the time the battalion was relieved on 28 August it had lost 46 killed and 141 wounded.
Split into simpler sentences: After three days the trenches were practically obliterated, forcing the men to occupy the shell holes in front of them instead. By the time the battalion was relieved on 28 August it had lost 46 killed and 141 wounded.