A Visit to Fort Mifflin on the Delaware

Historic Sites

August 6, 2020
by Rand Mirante Also by this Author


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The walls grew weak; and fast and hot
Against them pour’d the ceaseless shot
With unabating fury sent,
From battery to battlement;
And thunder-like the pealing din
Rose from each heated culverin
Lord Byron, “The Siege of Corinth,” VI

The enthusiast in search of the storied Revolutionary War bastion on the west bank of the Delaware needs to be alert and imaginative. Passing the fading hulks of warships anchored at the Philadelphia Navy Yard and descending southbound over the Schuylkill River from the Girard Point Bridge, the motorist should be on the lookout for the abrupt “Island Avenue” turn-off from I-95.[1] The name of this exit is both appropriate and irrelevant, since Fort Mifflin[2] is no longer situated on an island. The distinct geography of Mud Island, from which Mifflin once guarded the southern approach to Philadelphia, no longer exists, and neither do either of two adjacent islands, Province and Carpenter’s, which once directly faced Mud from the Pennsylvania side of the Delaware and from which British batteries battered the bastion. All three of these islands have disappeared as such, subsumed into landfill operations which enabled the creation of Runway 8-26 at Philadelphia International Airport. As the visitor turns from Island Avenue onto Enterprise Avenue, traverses a short tunnel, and approaches the chain-link entrance to the fort’s grounds, no evidence is visible of slender Mingo Creek, which once separated Province and Carpenter’s. Neither is there any apparent evidence of the depthless six-hundred-yard “inner channel” of the Delaware that separated Mud from its assailants’ artillery emplaced upon the two juxtaposed islands, and where the Royal Navy’s converted transport Vigilant also contributed to Mifflin’s eradication. Blasts from the periodic cannonade delivered over several weeks with increasing intensity 243 years ago by approximately one hundred Royal Artillery and Royal Navy cannons, howitzers, and mortars have been replaced by the whining drone of incoming airliners with landing gear down-locked in final approach to PHL; they seem barely to clear the fort’s walls.[3] In other words, while a walk within Mifflin’s ramparts will richly reward the aficionado of nineteenth-century coastal and riverine fortresses, those visiting solely for Revolutionary purposes will need even more active imaginations than usually required in visiting military sites of that era.

Leaving the parking area and bypassing the main entrance to the fort itself—which is an impressive example of later military architecture, containing several casemates along with barracks, officers’ quarters, an arsenal, an artillery shed, and a blacksmith’s workshop—the visitor should first head towards the west bank of the Delaware. He or she will note that the fort is surrounded by marshland forming an amphibian- and reptile-friendly natural moat replete with water lilies, reeds, sedges and cat-tails; all three former islands were reclaimed from mud flats and, depending on rainfall and the tide, they would be intermittently submerged. When Tom Paine briefly but bravely visited the fort in mid-October 1777 during the early stages of the siege, he noted that the British had fired “about thirty shells into it . . . without doing any damage . . . The ground being damp and spongy, not about five or six burst, and not a man was killed or wounded.”[4] That benign result would soon end, when the British built more batteries and started cutting the fuses on their exploding projectiles and favoring the use of solid shot to level Mifflin’s ramparts, parapets, palisades, traverses, blockhouses, and buildings. (British artillerists on Province and Carpenter’s Islands, serving under expert builder and aimer Capt. John Montresor of the Royal Engineers, also endured misery in the mud, as drenching autumn downpours resulted in fieldpieces and mortars sinking into the swampy soil along with their supporting platforms.)

From an exterior parapet, and with the aid of sharp eyesight or binoculars, one can spot roughly a mile-and-a-half across the river on the New Jersey side a column situated on a high bluff, on the site of Mifflin’s sister redoubt and co-protector of the Delaware, Fort Mercer; the column is topped by a statue of Col. Christopher Greene of the 2nd Rhode Island Regiment, under whose command the Americans bloodily repulsed a Hessian attack on October 23. The twin forts were supplemented by a Pennsylvania Navy fleet of sloops; row-galleys; gun-boats sporting evocative names like DragonHornet, Porcupine, Tormentor, Viper, and Vulture; and fireships, appropriately styled  CometVolcano, Vesuvius, Aetna, etc.[5] The more prosaically-titled row-galleys were a particularly serious asymmetrical nuisance: each mounted just one eighteen- or twenty-four-pound bow-gun but was highly maneuverable, shallow-draft, and presented an elusive, low-profile target for both shore-based and ships’ guns. The American flotilla was commanded by the capable but prickly Pennsylvania Navy Cdre. John Hazelwood, who had three Continental Navy vessels (a frigate, soon captured by the British; a brig; and a sloop) rather reluctantly reporting to him as well. The defenders of the Delaware also utilized a floating battery and, most seriously, two formidable lines of underwater barricades, sharpened stakes topped by spear-like metal caps and called chevaux-de-frise. They could readily tear a hole in the hull of any oncoming warship or transport, and the captains of Adm. Sir Richard Howe’s armada had a healthy respect for them; Admiral Howe reported to the Secretary of the Admiralty on October 25 that the barriers “were sunk so as intirely to render the nearer Approach of the Ships impracticable.”[6] In Fort Mifflin’s small but fascinating museum, the visitor can see some rather casually displayed iron spikes that were salvaged from the Delaware by the Army Corps of Engineers; also on view are an engaging diorama depicting an oncoming warship on the verge of having its hull perforated, and an adjacent, slightly antiquated but entrancing topographical model of the action on the Delaware (complete with helpfully labeled little ships and miniaturized chevaux-de-frise).

A diorama in the Fort Mifflin museum, left, and a portion of a chevaux-de-frise on display. (Author)

The problem for the Americans was that their two forts and the attendant obstacles were intended to block the British from taking the capital by moving up-river; however, Philadelphia had already been occupied on September 26 by the British Army under Gen. William Howe, marching overland following its victory at Brandywine and entering the city without firing a shot, as the Continental Congress fled to York. Rain-soaked and mud-splattered British engineers and gunners sent from Philadelphia were soon feverishly working under Captain Montresor’s direction on artillery emplacements on Province and Carpenter’s Islands, across the relatively narrow inner channel from Mifflin.

General Howe had a problem as well, and it was an existential and potentially catastrophic one: he unexpectedly found himself in a desperate race against the calendar. He was having grave difficulty provisioning his occupying army as well as the Loyalist and neutral (largely Quaker) inhabitants of Philadelphia, as the overland supply route to the city was treacherous and inefficient. As the effects of being denied essential water access to Philadelphia took hold and then escalated, Capt. John Peebles of the 42nd Regiment wrote, “provision very scarce & dear. Beeff 2/ & 2.6 P lb. Sugar a dollar.”[7] The Royal Navy, berthed nineteen miles south at Chester, was being obstructed by American defenses: primarily the chevaux-de-frise lines, each component of which was anchored to the river bottom and weighted down by large boxes filled with stones. Extracting each set of spikes required two vessels moored alongside, and the arduous removal process was one that Hazelwood’s galley flotilla, abetted by Jersey-side shore batteries, proved adept at thwarting.

The sands in General Howe’s hourglass were trickling down against his fortunes in two other inexorable ways: at some imminent point the Delaware would begin to freeze over and, also at some imminent point, Gen. Horatio Gates, following the surrender of Gen. John Burgoyne’s army, and in grudging compliance with Washington’s repeated demands, would relent and sparingly release a portion of his forces to bolster the Continental Army hovering outside Philadelphia.

It was under this increasing time pressure that the British made a coordinated but disastrous move against the Americans’ defensive network on October 23-24: they pummeled Fort Mifflin with a relentless cannonade but, as Paine had noted earlier, much of the shot from their twin shore-side islands sank into Mud’s muck and the defenders’ fortifications were to some extent quickly if haphazardly repaired; the Hessian overland assault on Fort Mercer was decimated and its commander, Col. Carl von Donop, was killed; and an attempt to get the Royal Navy into the fray culminated in the sixty-four-gun Augusta running aground and literally being blown sky-high, with a comparable fate for the eighteen-gun sloop Merlin. Captain Montresor thereupon glumly noted: “Somewhat dejected by Burgoyne’s capitulation and not elated with our late maneuvers as Donop’s repulse and the Augustas and Merlin being burnt and to compleat all, Blockaded.”[8]

Turning away from the Delaware to inspect the exterior of the nineteenth-century fort, the perceptive visitor will notice an oddity: while most of the outer wall is made with red brick, there is a lower portion of it comprised of sizable granite blocks facing eastwards toward the river. Ironically, it is this surviving original section that can be attributed to the same man who would help flatten Mifflin.

In 1771, the Pennsylvania Board of Commissioners had determined to build a fort on Mud Island, which interestingly had been purchased from the Speaker of the Provincial Assembly Joseph Galloway, whose legal title may have been somewhat shaky.[9] The man selected to be architect was none other than Fort Mifflin’s future nemesis: Captain Montresor, who was a survivor, along with George Washington, Horatio Gates, and Charles Lee, among others, of Gen. Edward Braddock’s 1755 defeat on the Monongahela. Montresor, who had been dispatched to Philadelphia by Gen. Thomas Gage, another veteran of the Braddock debacle, drew up elaborate and costly plans, commenting that “a good engineer is not unlike a good physician, who prescribes what is most beneficial without regarding expenses.”[10] His ambitious vision entailed a solid, bristling citadel which mounted thirty-two cannon, four mortars, and four howitzers, and was to have a 400-man garrison. The Assembly ignored Montresor’s medical analogy and the disgruntled engineer recorded in his journal: “The Commissioners were in favor of economy . . . even to rejecting the use of piles for a foundation.”[11] Montresor would also note with bitterness that he had never been paid for his plans nor for his travel expenses. He would exact his revenge.

Work did begin sporadically on a much scaled-down version of Montresor’s conceptualization of an invulnerable stronghold, and the partial, foundational stone wall which is still visible is all that remains of that first version of Mifflin; it was later incorporated into the post-Revolutionary fortress that began to take shape in the 1790s under the direction of Federal City planner Pierre Charles L’Enfant.[12] By October of 1777 the Americans’ suddenly-frantic work on the long-neglected Mud Island project had yielded palisades, parapets, ditches, dikes, floodgates, nasty anti-personnel holes with spikes on the bottom called trou-de-loups (i.e., wolf-traps), three blockhouses, and several garrison buildings. But by the end of the siege, little more than the east-facing original granite blocks would remain.[13]

Command of the fort during the siege itself became a problem. A Prussian adventurer and reputed fortifications expert, Col. Henry Leonard Philipe, Baron d’Arendt, was seconded to Mifflin by Washington, but he was wounded and was also alleged to have exhibited cowardice under fire.[14] The Baron pleaded illness and left for the New Jersey side of the river and beyond.  Lt. Col. Samuel Smith of the 4th Maryland resumed control and he proved a stickler for seniority, leading to significant tensions until he was oddly but seriously injured by a British shot coming down or through the chimney of one of Mifflin’s buildings and ricocheting out of the fireplace.[15] Maj. Simeon Thayer was thereupon dispatched by fellow Rhode Islander (and fellow survivor of the 1775 assault on Quebec) Colonel Greene from Fort Mercer to assume command at Mifflin. Thayer proved highly resilient, although he, like Smith, had disputes with the irascible and scrappy Commodore Hazelwood, who would take directions from no one. In the mix as well was the Marquis Francois Louis Teissèdre de Fleury, a discipline-minded and very capable and courageous engineer who had assiduously studied the writings of fortifications expert Sébastien Le Prestre de Vauban but had precious little to work with on Mud Island (he complained in his diary that “Varnum has sent me neither Ax, Fascine, Gabion, nor Palisade, although he promised me all these Articles”).[16]The likewise brave but fortifications novice Smith also tangled with the Marquis and with the Baron. In addition to d’Arendt and Fleury, Washington had sent Brig. Gen. James Varnum to coordinate the overall defense of the Delaware and settle disputes (which also included serious tensions within the leadership of New Jersey militia helping defend the east bank).[17]  Dismayed and exasperated by the incessant infighting and complaints directed his way, Washington wrote to Varnum from White Marsh on November 4, 1777:

I thank you for your endeavours to restore confidence between the Comr. [Commodore Hazelwood] and Smith. I find something of the same kind existing between Smith and Monsr. Fleury, who I consider as a very valuable Officer. How strange it is that Men, engaged in the same Important Service, should be eternally bickering, instead of giving mutual aid! . . . All our actions should be regulated by one uniform Plan, and that Plan should have one object only in view, to wit, the good of the Service.[18]

But by the time Varnum had established some control over the scene and a measure of coordination for the service’s good, and forces from Gates finally began to trickle down from the north, it was too late.

Following the Hessians’ failure to take out Fort Mercer and the Royal Navy’s disaster on the Delaware on October 23-24, at the not-always-appreciated and likely unnecessary urgings of General Howe, Captain Montresor continued his efforts to expand the batteries on Province and Carpenter’s Islands despite drenching downpours and harassing fire from Hazelwood’s pesky galleys and gunboats, from an American floating battery, and from Mifflin itself.[19] The British cannonades were sometimes intermittent, but they would reach levels of intensity whereby, starting on November 10, upwards of 1,100 shots per day were fired at Fort Mifflin by Montresor’s guns alone.[20] And by November 15, the Royal Navy had maneuvered its own version of a floating battery, a modified former East India transport vessel renamed Vigilant, into position to enter the inner channel alongside the fort and to direct point-blank fire at it. Vigilant, having been converted to shallow-draft in part by ditching some of her armaments, nevertheless still bristled with sixteen guns and carried a complement of soldiers and marines, who once next to the fort and within pistol range riddled the beleaguered garrison with gunfire and with grenades lobbed down from the tops and rigging. The fusillades and barrages from Vigilantwere massively augmented by a following shallow-draft British sloop, Fury, carrying three 24-pound cannons; by longer-range bombardment from two large warships, the seventy-gun Somersetand the fifty-gun Isis; and by ongoing, relentless fire from Montresor’s fourteen cannons, howitzers, and mortars.[21] The paymaster of the Pennsylvania Navy, William Bradford, informed Thomas Wharton, president of the state’s executive council, that “the large East India Ship that was cut down . . . got close to the Fort” and that together with Montresor’s five land batteries, it “tore the Fort all to pieces and knocked down all the Ambrusers [i.e., embrasures], killed many of our People and wounded more.”[22] Vigilant’s commander, Lt. John Henry, entered in his ship’s journal for the 15th under “Fireing on Mud Fort” that while his ship had received heavy fire from “Rebel Galleys & One of their Floating Batterys,” at 6 PM “the Fort was Silenced.”[23]

A 1778 map of the Delaware River below Philadelphia showing the positions of Fort Mercer on Fort Island, Fort Mifflin on Red Bank, and the Chevaux-de-frise at points across the river. A sketch of the profile and plan of the Chevaux-de-frise is at the bottom right. (Library of Congress)

Silenced and soon deserted, but technically not surrendered. The evacuating remnants of the fort’s stalwart garrison (at the high point perhaps numbering 400 men but now down to about 40[24]) left their massive flag, bearing thirteen alternating red, white, and blue stripes, flying proudly over the abandoned ruins of what that intrepid diarist and participant Pvt. Joseph Plumb Martin, one of those final few (including Thayer and Fleury) who escaped with their lives across the Delaware to New Jersey, would refer to as “our poor little fort, if fort it might be called.” Martin grimly observed that “the whole area of the fort was as completely plowed as a field . . . If ever destruction was complete it was here.”[25]

Testifying to the grimness of the Mud Island landscape was Admiral Howe’s personal secretary when he stepped ashore a week after the fort fell:

Nothing surely was ever so torn & riven by Cannon-Balls. A more dismal Picture of Ruin can scarce be conceived.  But if we had not taken it; it is said, we could not have been supported in Philadelphia.[26]

Hazelwood’s galleys were set ablaze by their crews on November 20, and Fort Mercer, facing a formidable force that had landed in New Jersey under Maj. Gen. Charles, Earl Cornwallis, was destroyed on November 21 by its withdrawing garrison. It had been a close-run thing: Maj. Gen. Nathanael Greene, who had been sent by Washington to observe the hostilities from as proximate a vantage point as possible, had reported back to his commander on the day before Mifflin was yielded up that “The enemy are greatly discouraged by the forts holding out so long and it is the general opinion of the best of the citizens that the enemy will evacuate the city if the fort [Mifflin] holds out until the middle of next week.”[27] But when Fort Mercer too was abandoned and blown up on November 21 the river was completely uncontested; Royal Navy work parties could thereupon commence opening gaps in the chevaux-de-frise lines without hindrance. Complete control had been achieved just in time by the Crown’s forces.[28] The release of their grip on Philadelphia would have to wait until the coming of spring.

Prior to the Americans’ forced and hasty departure from Mud Island, the Mifflin flag had briefly been taken down by the halyard so that a signal flag could be raised. Private Martin had briefly hesitated when his officers, hearing premature cheering from the nearby British, called for someone—anyone—swiftly to hoist the banner again. A sergeant promptly stepped forward before Martin could do so himself; upon accomplishing his mission the intrepid volunteer clambered down the flagstaff—“an old ship’s mast”—and was immediately “cut in two by a cannon shot.” Martin wrote: “This caused me some serious reflections at the time.”[29]

On gazing up at the large (but apparently down-sized from the original) banded banner which now flies over Fort Mifflin, today’s visitor can partake in his or her own serious reflection upon the brave and resilient defenders of the “poor little fort,” and upon the standard for which the defiant sergeant gave his life so long ago.


[1]Even the dedicated traveler-historian Benson Lossing encountered difficulty finding Mifflin in the 1820s: “We crossed the Schuylkill, and, passing through the cultivated country on its right bank, missed the proper road to Fort Mifflin.” Benson Lossing, Pictorial Field Book of the Revolution (New York: Harper & Bros., 1852), 2: 83.

[2]This piece will uniformly refer to “Fort Mifflin,” named in honor of Maj. Gen. Thomas Mifflin at some point in 1777; the British and some Americans as well would continue to refer to it by its previous name, “Fort Mud.” After the relationship between Mifflin and Washington fractured, the latter referred to the fort by its colonial name. See Jeffery M. Dorwart, Fort Mifflin of Philadelphia (Philadelphia: University of Pennsylvania Press, 1998), 59.

[3]My artillery estimate includes 14 land-based pieces, 19 cannon on the converted floating batteries Vigilant and Fury, and less than half the guns on eight other ships likely to have engaged with Mifflin at some point during the siege.

[4]Thomas Paine to Benjamin Franklin, May 16, 1778, Founders Online, National Archives, founders.archives.gov/documents/Franklin/01-26-02-0421.

[5]John W. Jackson, The Pennsylvania Navy (New Brunswick, NJ: Rutgers University Press, 1974), 342-43, 348-49.

[6]Richard Howe to Philip Stephens, October 25, 1777, Naval Documents of the American Revolution, ed. Michael Crawford (Washington, DC: Department. of the Navy, 1996), 10: 289.

[7]John Peebles, John Peebles’ American War, ed. Ira D. Gruber (Stroud, UK: Sutton Publishing Ltd., 1997), 148.

[8]John Montresor, Journals of Capt. John Montresor, ed. G.D. Scull (New York: New York Historical Society, 1882), 472.

[9]See Dorwart, Fort Mifflin, 15, where the author speculates that the Speaker may have influenced the decision to build on Mud Island despite the existence of one or more superior sites. Galloway would become a prominent Loyalist who re-entered Philadelphia in 1777 with Howe’s forces, provided intelligence about bombarding Mud Island, and eventually settled in Britain after being convicted of treason in absentia and having his estates confiscated. Ibid., 35.

[10]Montresor, Journals, 415.

[11]Ibid., 415.

[12]See Dorwart, Fort Mifflin, for a thorough continuation of Fort Mifflin’s history up through 1997, including the tangled politics involved in its preservation.

[13]Samuel Steele Smith, Fight for the Delaware 1777 (Monmouth Beach, N.J.: Philip Freneau Press, 1970), 39; Jackson, 237.

[14]Jackson, 210-211; McGuire, Thomas, The Philadelphia Campaign (Mechanicsburg, PA: Stackpole, 2007), 191.

[15]Smith, Fight for the Delaware 1777, 32.

[16]Journal of Francois Fleury, qtd. in Paul K. Walker, Engineers of Independence: A Documentary History of the Army Engineers in the American Revolution (Washington, D.C.: Office of the Chief of Engineers, U.S.G.P.O., 1981), 171. To this day the de Fleury Medal is awarded by the U.S. Army Engineer Association for “courage and boldness.” See, for example, https://www.tad.usace.army.mil/Media/News-Stories/Article/1997119/deployed-engineer-awarded-bronze-de-fleury-medal/

[17]Smith, Fight for the Delaware 1777, 42.

[18]George Washington to James Mitchell Varnum, November 4, 1777, The Writings of George Washington, ed. John C. Fitzpatrick (Washington, DC: U.S. Government Printing Office, 1933) 10: 5.

[19]See Montresor, Journals, 467, where the diligent and by then rather annoyed captain recorded that General Howe complained about purportedly slow progress on the construction of emplacements under American fire on the swampy terrain of Province and Carpenter’s Islands. Montresor’s respect for his commander-in-chief would be further eroded when Howe neglected to mention his engineer’s significant contributions to the British victory in a November 28, 1777 report to the Secretary of State for the American Department, Lord George Germain. Montresor acidly commented in a notebook: “This omission of my name being mentioned to the Secretary of State in the Commander-in-Chief’s letter, lost me my rank, and obliged me to resign my command.” Ibid., 417-18.

[20]Calculation based on Montresor’s journal entry for November 10, 1777, ibid., 474.

[21]Montresor, Journals, 474. Source for British ships’ armaments is Smith, Fight for the Delaware 1777, 46.

[22]William Bradford to Thomas Wharton, Jr., November 16, 1777, Naval Documents, 10: 513.

[23]“Journal of H.M. Armed Ship Vigilant,” November 15, 1777, Naval Documents, 10: 508.

[24]David G. Martin, The Philadelphia Campaign (Conshohocken, PA: Combined Books, 1993), 142. Men were being rotated on and off Mud Island and casualties evacuated to/from the New Jersey side throughout the course of the siege.

[25]Joseph Plumb Martin, The Adventures of a Revolutionary Soldier,Glazier, Masters, 1830, GALE Document No. GALECY0110051412, 67-68.

[26]Ambrose Serle, The American Journal of Ambrose Serle, Secretary to Lord Howe, ed. Edward H. Tatum (San Marino, CA: The Huntington Library, 1940), 264.

[27]Nathanael Greene, The Papers of General Nathanael Greene, ed. Richard K. Showman (Chapel Hill, NC: University of North Carolina Press, 1980), 2: 198.

[28]It is interesting to learn that, at least in Thayer’s apparent opinion, Mifflin could have held on longer had the Pennsylvania Navy galleys followed through aggressively on the Commodore’s instructions to attack Vigilant in the inner channel: “according to Major Thayer’s sentiments, we could have held the Island, had the Ship [Vigilant] been destroyed.” In a telling postscript, General Varnum advised his commander-in-chief that Colonel Greene (of Fort Mercer) offered to officer and man three galleys to take out Vigilant “or perish to a man,” and that there was a similar offer from an officer in the “continental fleet” (at that point down to two ships). Varnum added that “The Commodore possesses a fine Disposition [presumably meaning his willingness to fight] but cannot command his fleet.” Varnum to Washington, November 16, 1777, Naval Documents, 10: 514-15.

[29]Martin, The Adventures of a Revolutionary Soldier, 67.


  • Thanks very much for the correction! The Second RI also participated in the successful defense of Fort Mercer, but they were sent in under Colonel Angell as reinforcements for the First.

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