Complex sentence: The unusually wet weather had caused the attacks to be postponed until 10 August and the Battle of Langemarck (16--18 August); some of these objectives were still uncaptured after operations later in the month.
Split into simpler sentences: The unusually wet weather had caused the attacks to be postponed until 10 August and the 16--18 August Battle of Langemarck. Some of these objectives were still uncaptured after operations later in the month.