He was in Boston at the outset of the American Revolutionary War, and marched with Percy to relieve the British troops returning from Concord. He was appointed chief engineer in America and captain in late 1775. He was present at the Battle of Long Island the next year, and was present at the execution of Nathan Hale on 22 September 1776. It is said that he kindly sheltered Hale in his office, giving him pen and paper to write final letters to his family, and that the execution moved him deeply. He was sent to the rebel lines under flag of truce to report the event, and he conveyed Hale's last words to William Hull. Having been superseded as chief engineer, he was placed as aide-de-camp on the staff of General William Howe, but was later reinstated as chief engineer. On 13 January 1777 his home on Montresor's Island was burned.