In late 1775, Benjamin Church, the Director General, assigned McKnight to the Putnam House building, one of six hospitals of the army's Hospital Department in Cambridge, Massachusetts. He remained in that division, which supported Washington's army, until, during a period of great scarcity of medical and surgical supplies for the sick and wounded, McKnight went with other surgeons and physicians to North Castle, New York with Washington's army when the Battle of White Plains began in October 1776. The Continental Army lost the battle, and the British took Fort Washington and Fort Lee, which pushed Washington's ragged army south toward New Jersey in December 1776, which set the stage for the Battle of Trenton.