Complex sentence: Such a move did not go unnoticed by the Ming fleet, which detached several oar ships to give chase to the Portuguese water expedition, and pinned them down with artillery fire for an hour before De Mello ordered the barrels of water be abandoned and immediately re-embark.
Split into simpler sentences: Such a move did not go unnoticed by the Chinese, who detached several oar ships to chase the Portuguese who were ashore. Upon sighting the Chinese closing in, de Mello ordered the barrels of water be abandoned and immediately re-embark.