Complex sentence: A second convoy, including two APCs, was then sent to the rescue but was ambushed and at least three of its soldiers were killed and 16 were wounded before the rescue mission was forced to retreat.
Split into simpler sentences: A second convoy, including two APCs, was then sent to the rescue but was ambushed on the way. At least three of its soldiers were killed and 16 were wounded before the rescue mission was forced to retreat.