Siege of Fort Mifflin

**The Siege of Fort Mifflin: The Defense That Held the Delaware**

In the autumn of 1777, the American cause was faltering. British General William Howe had outmaneuvered General George Washington in a series of engagements around Philadelphia, including the American defeat at the Battle of Brandywine on September 11 and the inconclusive but costly Battle of Germantown on October 4. By late September, Howe's forces had marched into Philadelphia, the young nation's capital and largest city, forcing the Continental Congress to flee first to Lancaster and then to York, Pennsylvania. The symbolic and political blow was severe, but the British occupation came with a critical vulnerability. The Delaware River, Philadelphia's lifeline to the sea, remained under American control, guarded by a network of fortifications, river obstructions, and small naval vessels. Among these defenses, Fort Mifflin on Mud Island and Fort Mercer on the New Jersey shore at Red Bank stood as the principal obstacles preventing the Royal Navy from sailing upriver to resupply Howe's army. As long as these forts held, the British garrison in Philadelphia would be forced to haul provisions overland through hostile territory, a slow and dangerous process that left supply wagons exposed to Continental raiding parties and militia ambushes.

Fort Mifflin was a modest earthen and stone fortification, never designed to withstand a prolonged naval bombardment. Its garrison was small, typically numbering only a few hundred men at any given time, and conditions on the low-lying, marshy island were miserable even before the fighting began. Command of the fort passed through several officers during the siege, but Lieutenant Colonel Samuel Smith of Maryland played a particularly notable role in organizing the early defense and improving the fort's works before being seriously wounded in late October. After Smith was carried from the island, command eventually fell to Major Simeon Thayer of Rhode Island, who would lead the garrison through its most harrowing days. Commodore John Hazelwood commanded the small American flotilla of galleys and floating batteries that supported the fort from the river, engaging British warships when possible and providing what cover they could.

The British recognized that breaking the Delaware defenses was essential to sustaining their hold on Philadelphia. An initial attempt to reduce Fort Mercer on October 22 ended in a sharp American victory, as Colonel Christopher Greene and his garrison repulsed a Hessian assault force, killing their commander, Colonel Carl von Donop. This setback only intensified British determination. Through late October and early November, the Royal Navy positioned warships, floating batteries, and gun emplacements on nearby Province Island and Carpenter's Island, steadily tightening the noose around Fort Mifflin. The bombardment escalated day by day, but nothing compared to the onslaught that began on November 10. For five consecutive days, British warships — including the sixty-four-gun ship of the line HMS Somerset — poured cannon fire into the fort at close range. Estimates suggest that over a thousand cannonballs struck the island on the worst single day of the bombardment. The defenders huddled behind walls that were collapsing around them, enduring casualties, exhaustion, and constant exposure to the cold November elements. They repaired what they could each night, dragging timbers and earth into position to absorb the next day's fire.

By the night of November 15, Fort Mifflin had been reduced to little more than rubble and splintered wood. Major Thayer, recognizing that further resistance would mean the annihilation of his remaining men, ordered the garrison to set fire to what was left and evacuate across the river under cover of darkness. Fort Mercer held on briefly afterward but was abandoned on November 20 when a large British force approached, and American control of the Delaware finally collapsed.

Yet the six-week defense of Fort Mifflin had accomplished something of lasting strategic importance. By denying the British easy resupply for over a month, the garrison had weakened Howe's capacity to launch further offensive operations before winter set in. This contributed to Howe's decision to remain in Philadelphia rather than pursue Washington's army, which withdrew to Valley Forge in December. The suffering endured by the Fort Mifflin defenders — roughly four hundred casualties among a garrison that never exceeded that number at any one time — foreshadowed the grim endurance that would come to define the Continental Army during the winter encampment that followed. Their sacrifice, though often overshadowed by larger battles, remains one of the most remarkable stands of the entire Revolution.