British naval forces in North America and the West Indies were weaker Cause_change_of_strength than the combined Cause_to_amalgamate fleets of France and Spain , and , after some critical decisions Deciding and tactical missteps by British naval commanders , the French fleet of Paul de Grasse gained Getting control Control over Chesapeake Bay , blockading Cornwallis from naval support and delivering Sending additional land forces to blockade him on land .