Kurhessen, Hessen was devided in several states, was occupied by Prussia in 1866 because they fought on Austrian sides. So you can add Kassel and Waldeck to the city names. But in 1866 Hessen mercenaries didn´t exist any more!
In the time of the American revolution Frederic the Great ruled Prussia. He was allied with Britain but he didn´t like his cousin very much and also because of his enlighted reign he tried to help the Americans by sending a good training officer, General von Steuben, to the colonies to make from farmers with guns real soldiers. Because he had trouble with Austria, Bavarian succession war, he couldn´t do more. After the war was over, he joined the first armed neutrality to cope with the danger of British attacks on neutral ships. In this neutrality, together with France, Sweden, Russia and Hamburg, Lübeck and Bremen Prussian ships formed convoys to defend themselves. So important goods passed the blockade. The British would have risked a war with the European powers if they had attacked the convoys. IIRC it were Hessian soldiers mostly who fought on the British side, and no Prussians.
Adler