Complex sentence: They remained in the line throughout August and September undertaking further attacks at Biaches and Mont St Quentin, before undertaking their final engagement of the war on the night of 3 October 1918, when they took part in the Battle of Beaurevoir.
Split into simpler sentences: They remained in the line throughout August and September undertaking further attacks at Biaches and Mont St Quentin. Their final engagement of the war came on the night of 3 October 1918, when they took part in the Battle of Beaurevoir.