Germantown was another American defeat. Nevertheless, both sides realized that the battle had been a close-run thing. Washington had had the temerity to attack Howe's own camp, and for a time he seemed on the verge of shattering the British army. Germantown almost became a Pennsylvanian Saratoga.

Washington remained in the vicinity of Philadelphia after the Battle of Germantown. Detachments of American troops kept the British from foraging for supplies in the countryside. Howe's route from the Chesapeake was far too long and exposed to attack to serve as a line of supply and communication with his brother's fleet. New Jersey was out of the question for the same reason.

The only feasible way to supply Howe's army was up the Delaware River. Washington also recognized this. He wrote that if Howe could be prevented from drawing supplies by water, “the acquisition of Philadelphia may, instead of his good fortune, prove his ruin.” The Americans constructed two forts and a series of obstacles to keep British transports from sailing up the Delaware.

Howe fought hard to open his line of supply in the months after Germantown. He began by capturing a redoubt at Billingsport, New Jersey, that guarded the way to the American strongpoints of Fort Mifflin and Fort Mercer. To protect the Delaware, the Americans employed chevaux-de-frise. These were large boxes made of logs that were filled with stones and sunk to the bottom of the river. Heavy iron-tipped beams facing downstream were fixed in them. In theory, any ship running into the beams would be ripped open, but the British navy dismantled the chevaux, clearing a passage to the forts.

Howe sent 2,000 Hessians under the command of Colonel Carl von Donop against Fort Mercer on the New Jersey shore. Colonel Christopher Greene and 400 Continentals defended the fort. On October 22, the Hessians stormed the fort in two columns. Greene let them get to the wall before ordering his men to open up with grapeshot and volleys of musketry. The Hessians were cut down by the score. When Colonel von Donop was mortally wounded, they abandoned the attack. Almost 400 Hessians were killed, wounded, or captured. The American casualties were less severe — fourteen men dead and twenty-three wounded. Four British warships attempting to assist the ground assault ran aground. One frigate was set on fire by American cannonading and blew up. A sloop could not be floated and was burned by its crew.

The British next turned their attention to Fort Mifflin, which sat on an island in the middle of the river. Badly laid out, a contemporary called it “a Burlesque upon the art of Fortification.” Its only strong walls faced downriver; elsewhere, it was badly exposed. The British built gun batteries on nearby islands and brought up a floating battery that they anchored forty yards from the fort. The bombardment began on November 10. Fort Mifflin was slowly knocked to pieces under an around-the-clock barrage. Six British warships joined in the assault on November 15. The Americans were hit by 1,000 shot fired every twenty minutes. What was left of the fort was destroyed. That night thesurviving American garrison escaped. They had lost 250 men defending the place.

Fort Mercer now became untenable. The British closed in by water and land. General Cornwallis brought up 2,000 men to launch another assault. Colonel Greene decided that the odds were too long and evacuated the fort on November 20. A small American fleet was burned to keep it out of the hands of the enemy. Howe had successfully opened up a secure line of supply.

Washington rested and rebuilt his army after Germantown. He unsuccessfully tried to distract Howe from the Delaware River forts with some maneuvering. Word came of the victory at Saratoga, followed by reinforcements of Continentals sent south by Gates. Washington began mulling plans to attack Philadelphia.

Howe withdrew from his exposed position at Germantown on October 19 and fell back to a chain of fortifications around Philadelphia. He made a last attempt to drive off Washington on December 4, making a night march toward Washington's camp at Whitemarsh. Scouts warned Washington of Howe's movement, and the Americans were ready. Howe probed Washington's heavily fortified lines for a few days. After a few skirmishes, he decided the American position was too strong and returned to Philadelphia. Washington and his army had won a moral victory.