Complex sentence: The command was first established in 1781 with the fleet usually anchored at Yarmouth Roads, its initial role was that of trade protection with the advent of the Napoleonic Wars it turned to that of blockading enemy ports.
Split into simpler sentences: The command was first established in 1781 with the fleet usually anchored at Yarmouth Roads. The fleet was also involved in trade protection with the advent of the looming Napoleonic Wars and later it turned to the blockading enemy ports.