Were the Germans involved in the American revolutionary war?

Yes. The British boasted that they had the best professional army of 50,000 men (this was later increased), but George III, in addition, had the funds to hire foreign soldiers, and about 30,000 Germans called Hessian's By-the-way the British also enrolled about 50,000 American Loyalists as well as American Native tribes. After Bunker Hill the King slammed any door of reconciliation with the colonies and in Aug. 1775 he proclaimed the colonies in rebellion. He soon hired thousands of German troops. Six German princes, involved in the deal, needed money and George needed the men. The news of the Hessians shocked the colonists. They thought of it as a "family" quarrel and now the King was adding "foreigners." The Hessians were good soldier's but they were more interested in booty than in duty and were called "Hessian flies." Finally, hundreds of them deserted and remained in the United States to become citizens. It was at Trenton on December 26, 1776 that Washington crossed the Delaware River and captured a thousand Hessians where were sleeping off their Christmas party.