At Lee’s Mill on April 5, 1862, Union Maj. Gen. Erasmus D. Keyes’s IV Corps, advancing up the Peninsula after marching along the Great Warwick Road through Young’s Mill, was checked at the Warwick River crossing by Brig. Gen. Lafayette McLaws’s 1,800 Confederate troops and three guns amid rain, nearly impassable roads, and extensive fortifications. Brig. Gen. William F. “Baldy” Smith’s lead division halted as it approached the river under fire, and Keyes quickly concluded that his flanking movement against Magruder at Yorktown had been blocked by a strongly fortified line behind the Warwick River, where dams had destroyed the fords and the approaches ran through dense forests, swamps, and marshes. Union chief engineer Brig. Gen. John G. Barnard agreed that the line was among the most extensive known in modern times. Although the engagement cost the Confederates ten casualties, its importance was far-reaching, because the unexpected strength of the entrenchments led McClellan to bring forward 103 heavy guns and besiege Magruder’s defenses.
