Complex sentence: The 7th Division was shelled by British artillery all the way to the Comines canal, then part of the division was diverted to reinforce the remnants of the front divisions holding positions around Hollebeke.
Split into simpler sentences: The 7th Division was shelled by British artillery all the way to the Comines canal. Part of the division was then diverted, to reinforce the remnants of the front divisions holding positions around Hollebeke.