In October–November 1777 British forces move to force the Delaware River and break Philadelphia's supply lines. Fort Billingsport falls, the Cheval de Frise is attacked, and the campaign pivots on Fort Mercer and Fort Mifflin.

Hessian assaults on Fort Mercer are repelled, while sustained naval and land bombardment reduces Fort Mifflin until its garrison withdraws. These actions reopen the river, relieve British supply pressure, and change the campaign's course.

Though not decisive battlefield victories, the forts' resistance buys crucial time for Washington's army and the Revolution, shaping the next phase of the war.