Complex sentence: South of Grandcourt, at the 173rd regiment was overrun by the time they emerged from their dug outs but the British battalion (8th North Staffordshires) had pressed on and was cut off and eventually surrendered.
Split into simpler sentences: South of Grandcourt, at the 173rd regiment was overrun by the time they emerged from their dug outs. The British battalion (8th North Staffordshires) pressed on and was cut off and eventually surrendered.