American Revolution: Siege of Fort Mifflin

Lt.Col. Samuel Smith during the American Revolution
Lieutenant Colonel Samuel Smith. Photograph Source: Public Domain

Siege of Fort Mifflin - Conflict & Dates:

The Siege of Fort Mifflin was fought September 26 to November 16, 1777, during the American Revolution (1775-1783).

Armies & Commanders


  • Lieutenant Colonel Samuel Smith
  • Major Simeon Thayer
  • Commodore John Hazelwood
  • approximately 450 men


Siege of Fort Mifflin - Background:

In late summer 1777, General William Howe elected to move south from New York to conduct a campaign against the American capital of Philadelphia.

  Traveling by water, his men landed at Head of Elk, MD in the Chesapeake Bay on August 25 and began marching north towards Pennsylvania.  On September 11, the British engaged and won a victory over General George Washington's army at the Battle of Brandywine.  The following two weeks saw Washington and Howe conduct a campaign of maneuver west of the city.  During this time a detachment of the American army led by Brigadier General Anthony Wayne suffered a bloody defeat at the Battle of Paoli.  On September 22, Howe succeeded in achieving an uncontested crossing of the Schuylkill River and four days later occupied Philadelphia.

Having taken the city, the British commander sought to open the Delaware River in order to allow his army to be supplied by sea.  These efforts were blocked by the American defenses downstream which included Forts Mifflin and Mercer, obstructions in the river, and Commodore John Hazelwood's small flotilla from the Pennsylvania State Navy.

  While Fort Mercer was located on the New Jersey shore, Fort Mifflin was sited on Mud Island in the middle of the river.  Designed by Captain John Montresor, construction of the fort began in 1771 and the walls on the river side were built of stone.  As funding ran short, work on Fort Mifflin ceased.

  With the beginning of the American Revolution, Continental forces completed the fort using a mix of wooden palisades and earthen walls.  Protected by a mixed battery of artillery, the fort was surrounded by sharpened logs and trous-de-loups (tiger pits).

Siege of Fort Mifflin - Smith Arrives:

Shortly before the fall of Philadelphia, Washington dispatched reinforcements to Fort Mifflin.  Led by Lieutenant Colonel Samuel Smith, who would later gain fame defending Baltimore during the War of 1812, troops from the 4th Maryland Regiment and additional Continental forces reached the fort.  Though Washington directed Colonel Baron Henry L. d'Arendt to command the garrison, the Prussian's failing health prevented him taking an active role and oversight of operations fell Smith.  Fort Mifflin received additional troops on October 18 when Lieutenant Colonel John Green arrived with forces from Virginia.  To further protect the fort, American forces broke dikes along the river to prevent the British use of adjacent Province and Carpenter's Islands.

Siege of Fort Mifflin - Howe Moves:

Having defeated Washington at the Battle of Germantown on October 4, Howe shifted additional attention to the situation on the river.

  While a battery had been constructed at the mouth of the Schuylkill River, he ordered Montresor, who was serving as an engineer in his army, to begin constructing artillery positions atop the dikes on Carpenter's Island.  Beginning this work on the night of October 10, Montresor's men were attacked by Smith and Hazelwood the next day.  In the action, the Americans captured 58 men from the 1st Grenadier Battalion.  On October 14, French engineer Major François-Louis Teissèdre de Fleury arrived and began making improvements to the fort's defenses.  Four days later, Hessian troops under Colonel Carl von Donop suffered a bloody repulse at Fort Mercer in the Battle of Red Bank.      

Siege of Fort Mifflin - Disaster on the River:

As von Donop struck, a British squadron moved up the river in support.

  Led by Captain Francis Reynolds in the ship of the line HMS Augusta (64 guns), this force commenced a bombardment of Fort Mifflin in anticipation of landing troops.  Maneuvering off Mud Island, Augusta and the sloop HMS Merlin (18) both ran aground.  Unable to free themselves during the night, both came under intense American fire the next morning.  Though HMS Isis (50) attempted to provide aid, it could not free Augusta and shortly thereafter the stricken ship caught fire and exploded.  Seeing this, the crew of Merlin set the sloop on fire and abandoned ship.  On October 26, a severe storm hit the area flooding Fort Mifflin and the British batteries on the western shore.

Siege of Fort Mifflin - Seeking a Decision:

In Philadelphia, Howe's supply situation became increasingly desperate as Washington's men cut off the land routes to the city.  As a result, the British were compelled to sneak supplies past the forts at night using flatboats.  On October 28, Washington directed Brigadier General James Varnum to assume control of the Delaware defenses.  Part of his brigade was already manning the river forts and on November 3 the remainder was committed to Fort Mifflin.  As Varnum worked to reinforce the fort, Montresor continued to expand the British batteries.  These eventually contained two 32-pdrs, 6 24-pdrs, 1 18-pdr, 2 8" howitzers, 2 8" mortars, and 1 13" mortar.  On November 10, Montresor commenced a prolonged bombardment of the fort.

Under fire all day, the garrison did not suffer any casualties but the large sections of the western defenses were severely damaged.

 As the fort was bombarded the next day, Smith was hit by a spent round and wounded.  With Smith's evacuation the next day, command ultimately devolved to Major Simeon Thayer.  Inside the fort, Fleury struggled to organize work details to repair the walls and remount guns.  By November 13, Montresor's batteries had grown further and Lieutenant Colonel Sir George Osborn moved forward to prepare a light infantry force for an assault.  Two days later, a specially-design shore bombardment ship, HMS Vigilant (20), approached Fort Mifflin and opened fire from a range of twenty yards.  

Supported by other British warships in the river, Vigilant pounded the fort's walls.  As the bombardment progressed, Fleury fell unconscious and the garrison attempted to call for assistance from Hazelwood.  Though American naval forces approached, heavy British fire prevented them from rendering aid to the fort.  On shore, Osborn's men prepared to attack but were prevented from advancing by Howe who hoped the Americans would abandon their position.  With the fort in ruins, Thayer made the decision to retreat to the New Jersey shore that evening.  After salvaging what remained, American forces withdrew to Red Bank.  Shortly after midnight, the last troops burned the fort's barracks before departing.  

Siege of Fort Mifflin - Aftermath:

Around 6:00 AM on November 16, Osborn's troops crossed to Mud Island and occupied Fort Mifflin.  Entering the ruins, they were stunned at the carnage they found.  In the defense of Fort Mifflin, American forces sustained around 250 casualties while the British incurred around 120 killed, wounded, and captured.

 Having taken Fort Mifflin, Howe directed Lieutenant General Lord Charles Cornwallis to take 2,000 men across the river to assault Fort Mercer.  Warned of the impending threat, the Americans abandoned the fort allowing Cornwallis to capture it on November 20.  With the fall of the forts, Hazelwood was forced to burn his ships eliminating the last line of resistance on the river.  

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