Trenchard was aboard the "Powhatan" at the during the Battle of Taku Forts in June 1859, when Commodore Tattnall, observing the desperate position of the British and French forces attempting to force their way up the Peiho river, exclaimed "Blood is thicker than water!" and went to their assistance despite the United States's neutrality in the conflict. Soon after, when the United States concluded a treaty with China, Trenchard was part of Ambassador John Elliot Ward's retinue that traveled to Peking where treaties were formally exchanged. "Powhatan" then returned to the United States.