In the late 18th Century, privateers were ships commissioned by governments to pillage, steal and burn merchant vessels. But few people know that during the Revolutionary war one band of privateers sailed under the orders of one of our greatest statesmen: Benjamin Franklin. In 1778, while ambassador to France, Franklin hired privateers to capture British sailors and use them to exchange for the Americans held by the British in insufferable conditions. National Geographic dives into the Irish Sea with a group of underwater explorers on an expedition to investigate this piece of little known American history.