Fort Mifflin

A War of Posts

Over eight years of struggle, the American Revolutionary War lurched from guerrilla war to limited war, and occasionally a war of maneuver. But the exigencies of 18th-century warfare in an expansive area of operations characterized by rough terrain, dense forests, and uncooperative rivers made it at almost all times, a war of posts. A war of posts is often like a chess match, with deliberately placed defensive positions aimed at securing supply lines, blocking an enemy advance, and securing critical regions. Think of the game Risk, but with real men and sweat and toil, not little wooden or plastic markers. The struggle for North America had several key engagements involving fixed fortifications. In many ways these defined the war: West Point and Ticonderoga come to mind. But there were many with temporary or hastily built fortifications. These proved crucial as well. Fort Moultrie, Stony Point, and Yorktown provide examples.

Fort Ticonderoga

The Siege

The war included several key sieges. Most were of short duration with one side capitulating or the other breaking off the siege due to external factors such as weather, supply, or advancing reinforcements. Fort Stanwix, Savannah, Charleston, and Newport are examples. Yet even a short-lived defense of a post could buy precious time for a commander to gather forces, regroup, maneuver to advantage, or just get the heck out of Dodge. That is one reason that a commander, when forced to a long investment of a post, or more importantly, forced to storm a post, harshly treats the defenders and any hapless civilians left at the end. Ironically, those occasions where the British treated the defenders harshly merely fed rebel propaganda, which played no insignificant part in the struggle. Not only were the American populace keenly observing things - the entire world was watching. That is material for another post, however.

Fort Stanwix

Fort Mifflin

Arguably longest active defense of a post under siege in the war was also one of the least celebrated. We will try to move the needle in the direction of celebration. Fort Mifflin lies on the Delaware River, in today's South Philadelphia, at a place called Mud Island. Construction on the fort began in 1772 to bar the approach to the city.  Ironically the original construction was under the famous British engineer officer Captain John Montessor. The fort was completed in 1777 under the direction of American Major General Thomas Mifflin, from whom it draws its name. It protected a line of water obstacles that stretched across the river to sister fort, Fort Mercer, in New Jersey.

Maj Gen Thomas Mifflin
finished construction of the fort that bears his name

Most Formidable Defenses

A fort covering a sea approach needed more than stout walls and good fields of fire. So Philadelphia built a series of chevaux de frise, placed in "tiers" beneath the waters of the Delaware between Forts Mercer and Mifflin. They were built into wooden-framed boxes, 30 feet square, made from huge timbers lined with pine boards. The engineers sunk these frames into the riverbed. Each box was filled with 20 to 40 tons of stone to anchor in place. Each frame had two or three large timbers tipped with iron spikes set underwater and facing obliquely downstream. These chevaux made for a powerful obstacle that posed a danger to unwitting ships. The string of chevaux had gaps so friendly shipping could pass. The location of these safe passages was a highly guarded secret. Any British ship not impaled on the spikes or caught up in the chain still risked trained fire from the forts themselves.

Sketch of chevaux crates filled
with stones

A Strategic Position

The British captured Philadelphia in September 1777 by an overland campaign that avoided the fortified Delaware approach. But the British commander in chief, General William Howe now faced the need to open his line of communications to the sea.  He needed the protection of the Royal Navy and an open supply line or his position in Philadelphia could become a liability. The British commander realized that their command of the sea was an invaluable advantage over the Americans that must be used to maximum advantage. Howe's brother, Admiral Richard "Black Dick" Howe, commander of the Royal Navy in America, had already begun reducing American defenses downriver. But brother Billy could not wait for their arrival. He needed to move overland against Fort Mifflin and save the navy for Fort Mercer on the Jersey side.

Control of lower Delaware River and bay
was crucial to British success

Doughty Defenders

Samuel Smith

But the American commander in chief, General George Washington, also recognized the value of the Delaware. Driven from the vicinity of the capital after his defeat at German town, Washington prepared for a long series of operations aimed at disrupting British plans to solidify their hold on Philadelphia. On 23 September, Washington sent Lieutenant Colonel Samuel Smith of the 4th Maryland Regiment with a detachment of Continentals into the fort on Mud Island on the Delaware River. Readers may recall I profiled this first patriot in an earlier Yankee Doodle Spies post. Smith's initial force numbered 200 soldiers plus Major Robert Ballard of Virginia, Major Simeon Thayer of Rhode Island, and Captain Samuel Treat of the Continental Artillery. Resolved to thwart British efforts at whatever cost, the Continentals went to work preparing the defenses while summoning more troops for the defense. Eventually, they would have 400 men, not nearly enough to adequately garrison a fort of Mifflin's size. This was a problem that plagued other forces attempting to hold forts Ticonderoga and Washington. Yet Smith and his men resolved to make the most of the fort.

Fort Mifflin plans

The British Approach

John Montressor

General Howe ordered a move on nearby Providence Island on 10 October 1777. Washington's land forces resisted but were quickly driven off, and soon heavy siege guns were set into battery facing the American fort. Formidable as it was, Fort Mifflin had not been heavily fortified for a threat from Philadelphia. In no small bit of irony, Captain John Montresor, earlier designer, and builder Fort Mifflin planned and built the siege works used against his fort. Things were certainly stacked against the rebels. Soon, heavy balls came crashing into the American positions. The pounding against that side of the fort was horrific, but the Americans fought back gallantly, inflicting heavy damage on several British ships that tried to force their way upriver. The British mounted guns on floats, forming water batteries that edged closer to the beleaguered outpost. American casualties mounted and supplies dwindled over the month of horrific bombardment and deprivation.

The Royal Navy Engages

"Black Dick" Howe -
so named for a swarthy complexion

But Billie Howe's brother,  "Black Dick", would have the last say. He was finally able to unleash the Royal Navy. On 10 November, a floating battery of twenty-two heavy 24-pound guns closed to within 40 yards of the fort. At point-blank range, the British gunners could have their way, big time. This turned out to be the heaviest bombardment of the Revolutionary War.  Shot and shell pounded walls and buildings to pieces. Defenders had limbs torn away or crushed. The battle was tilting toward the besiegers but Smith and the defenders were determined to defend the fort. The cold weather was coming early and if they could hold until the Delaware froze the British supply line might be cut, forcing Howe's army to abandon the recently captured capital. On the British side, word of the catastrophic surrender of Major General John Burgoyne's army at Saratoga put pressure on both Howe brothers. A victory over the stubborn defenders would help offset the obvious drop in morale. The stakes were high for both sides!



The Pennsylvania navy (yes, they had a navy) came to the aid of the forts guarding the Delaware approaches.  Commodore John Hazelwood, with a sizable fleet of galleys, sloops, and fire-vessels launched several raids on British positions onshore and constantly harassed British river operations while patrolling the waters around the fort. But British naval strength eventually held sway. Rebel resistance continued. Cold, ill and starving, the garrison, reduced to much less than 200 the original 400-450 men, refused to give up. Under the direction of French Major Francois de Fleury, an engineer of extraordinary energy, the Americans worked each night to repair the damage of the day. Fleury himself was wounded in the battle.  A British ship of the line and sloop o' war both ran aground under the pummeling fire from Mifflin's defenders. But British naval superiority virtually guaranteed a bad outcome. Undercover of the murderous fire from the big guns of the floating battery, the British naval vessels closed in and soon British marines were sniping at the fort from high up in the rigging. With almost all their guns knocked out of action, the Americans were running out of options - but not out of gumption.

Fort Mifflin aka Mudd Island
was the key to the Delaware

The Final British Assault

Clear weather on 15 November gave the British a chance to turn up a final blast of heat.  They sent two ships,  Vigilant and Fury, with nineteen guns up the backchannel to the west of Fort Mifflin.  At the same time, three large ships armed with 158 cannon anchored directly offshore of the fort, in the main channel of the Delaware. To the east, three more vessels armed with some 51 guns ensured Mifflin's enfilade from all sides. A trap of smoke, fire, and iron.

The Royal Navy had to commit
massive resources to subdue the fort

To counter this British juggernaut, the defenders of Fort Mifflin had only ten cannons left. Soon, hundreds of cannonballs began blasting what was left in the fort. The large-caliber 18 and 24 pound balls tore through the defenders in another shower of smoke and fire. During the heaviest hour of the bombardment, some 1000 shots were fired into the fort. To add to the defenders' misery, British Marines climbed to the crow’s nest of Vigilant toss grenades at the fort's defenders. The defenders bravely fought on but suffered for it as casualties mounted. They returned fire until all their guns were silenced by the heavier British shot.  Lieutenant Colonel Smith was seriously wounded and had to be evacuated. The end was near.

The End

Nightfall found the surviving defenders exhausted, cold, and out of ammunition. But not out of options. The new commander of the fort, Major Simeon Thayer decided to evacuate the now indefensible Mifflin. Under the cover of darkness. the garrison rowed their way with muffled oars to Fort Mercer. Forty men volunteered to stay on and set fire to what was left.  Their work done, around midnight, they too crossed the Delaware to the safety of New Jersey. But Thayer decided on one last act of resistance. So as the last of Mifflin's valiant defenders rowed to safety they would see it ablaze - but they would see the flag still flying in a final gesture of defiance.

The unusual-looking flag that flew over Fort Mifflin during
the long siege and in a final act of defiance

The Result

During the siege, some 400 American soldiers held off more than two thousand British troops and 250 ships. The Americans suffered over 250 killed and wounded and lost the fort. But the time and resources expended by the Howe brothers to take the fort and control the Delaware enabled Washington to deploy his army to White Marsh and ultimately get to the safety of winter quarters at Valley Forge where a new American army was born.

A new American army would emerge from
the hard winter at Valley Forge

Aftermath

Fort Mifflin was rebuilt after the war and used for many years as a US base, providing (of course) one of the strategic harbor defenses for Philadelphia. Later it became a historic site. But of the original Fort Mifflin, only the white stone walls of the fort still survive today. The pockmarks in these stone walls give evidence of the intensity of the British bombardment of 1777. Local residents know this siege and massive bombardment as the Battle of Mud Island. But this once critical piece in the defense of the Delaware and Philadelphia never again saw military action.