Fort Mifflin
On the Delaware

Fort Mifflin Road
Philadelphia, PA 19153

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Fort Mifflin

In 1771, a British captain of the Royal Engineers named John Montresor was selected by Pennsylvania Governor John Penn to prepare plans for fortifying the waterborne approaches to Philadelphia. Montresor chose Mud Island because it offered protection to both the Schuylkill and Delaware Rivers.

Work began on the fort in 1772, but proceeded slowly until the outbreak of hostilities between England and the Colonies. By 1775 war seemed imminent. Attention was once again turned to the defenses along the Delaware River, and General Thomas Mifflin was charged with completing the work of "Fort Island" (as it was called at the time.)

Pierre Nicole's "View of Mud Island before its Reduction 16th Novr. 1777 under the Direction of John Montresor Esqr."

Work on the fortification continued through 1777. Artillery batteries were setup to defend the main channel of the Delaware River, and a dockyard was built to help maintain the small flotilla of gunboats from the Pennsylvania Navy. The chevaux-de-frise was constructed at several locations along the Delaware River's main channel, and only those river pilots with the secret knowledge of these submerged obstacles could take a ship safely to or from Philadelphia.

In September of 1777 the British made their first move to breech the American river defenses. The American fortification at Billingsport, only three miles down-river from Fort Island, fell to British land forces with little resistance. The only thing that now stood between the massing British fleet and Fort Island was the Pennsylvania Navy and the chevaux-de-frise.

From September to November the British Navy worked at moving and careening the chevaux-de-frise, and despite attacks from the American gunboats, the British managed to clear a channel through which their heavier warships could pass. At the same time, British artillery from Philadelphia moved south across Webb's Ferry and mounted batteries on Province and Carpenter's Islands. From there they were able to lay their guns on the less protected west side of Fort Island.

Detail of James Hamilton's painting "The Explosion of the Frigate Augusta and Burning of the Merlin at the Bombardment of Fort Mifflin, 1777"

By November 10th the British were in a position to launch a full scale attack on Fort Island, and on November 15th a coordinated effort of both British land and naval batteries reduced the fort to ruins. What remained of the fort's garrison escaped by boat across to Fort Mercer under the cover of darkness, leaving a handful of men at the fort's few remaining guns to create a covering diversion.

On November 20th, the outnumbered American garrison at Fort Mercer withdrew ahead of the advancing British forces. The loss of Fort Island and the surrender of Fort Mercerd the Delaware River to the British and allowed General Howe's army in Philadelphia to receive the supplies it desperately needed. However, the supplies came too late for the campaign of 1777 to continue. Winter was rapidly approaching, and a new campaign would have to wait until spring of 1778.

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