Louis Lebègue Duportail, a lieutenant colonel in the French Royal Corps of Engineers, was secretly sent to North America in March 1777 to serve in George Washington's Continental Army. In July 1777 he was appointed colonel and commander of all engineers in the Continental Army and, on 17 November 1777, he was promoted to brigadier general. When the Continental Congress created a separate Corps of Engineers in May 1779, Duportail was appointed as its commander. In late 1781 he directed the construction of the allied U.S.-French siege works at the Battle of Yorktown.