Volume 11 of the Revolutionary War Series contains correspondence, orders, and other documents covering one of the most militarily active periods of the war. The volume begins with Washington's army camped about twenty miles north of Philadelphia. Having planned to march toward the Hudson River to engage General John Burgoyne's northern expedition, Washington had to change course when scouts sighted the British fleet carrying General William Howe's army in the Chesapeake Bay on 22 August. Three days later Washington's troops were at Wilmington, Delaware, when Howe's army began landing at the head of the bay. Having personally led reconnaissance parties quite close to British lines, Washington then positioned his army on Brandywine Creek in Pennsylvania to halt Howe's subsequent march to Philadelphia, but on 11 September the Americans suffered a nearly disastrous defeat. After another American attempt to stop the advancing British was frustrated by a fierce rainstorm, Howe skillfully outmaneuvered Washington before turning to Philadelphia, taking possession on 26 September as Congress fled the city.

Washington still hoped to reverse Howe's apparent victory, but his attack on British positions at Germantown, Pennsylvania, on 4 October was hampered by his complicated plan of attack, battlefield confusion, and stout British resistance, which combined to defeat the Americans. No longer able to come to grips with Howe's main army, Washington turned his attention to blocking passage of the Delaware River to prevent supplies from reaching the British in Philadelphia. American hopes of recapturing Philadelphia looked dim.