Siege of Fort Mifflin The Siege of Fort Mifflin or Siege of Mud Island Fort from September 26 to November 16 , 1777 saw British land batteries commanded by Captain John Montresor and a British naval squadron under Vice Admiral Lord Richard Howe attempt to capture an American fort in the Delaware River commanded by Lieutenant Colonel Samuel Smith . The operation finally succeeded when the wounded Smith ' s successor , Major Simeon Thayer , evacuated the fort on the night of November 15 and the British occupied the place the following morning . Owing to a shift of the river , Fort Mifflin is currently located on the north bank of the Delaware adjacent to Philadelphia International Airport . After General Sir William Howe ' s British - Hessian army occupied Philadelphia , Pennsylvania on September 26 , 1777 , it became necessary to supply his troops . Fort Mifflin on Mud Island in the middle of the Delaware and Fort Mercer at Red Bank , New Jersey , together with river obstructions and a small flotilla under Commodore John Hazelwood prevented the Royal Navy from shipping provisions into the city . With Philadelphia effectively blockaded by the Americans , the Howe brothers were forced to lay siege to Fort Mifflin in order to clear the river . A Hessian attempt to storm Fort Mercer failed with heavy losses on October 22 in the Battle of Red Bank . Two British warships which had run aground near Mud Island were destroyed the next day . Major General George Washington reinforced Fort Mifflin throughout the siege , but the garrison never numbered more than 500 men . After a few setbacks , the British finally assembled enough artillery and warships to bring Fort Mifflin under an intense bombardment beginning on November 10 . No longer able to reply to the British bombardment , Thayer ordered the survivors to row across to New Jersey in the night and left the flag flying . Fort Mercer was abandoned soon afterward , opening the Delaware and permitting the British to hold Philadelphia until June 1778 . Background . After the British defeated the American army at the Battle of Brandywine on September 11 , 1777 , Howe failed to follow up Washington ' s withdrawal to Chester , Pennsylvania . From that town on the Delaware , the Americans marched northeast through Darby to cross the Schuylkill River at the Middle Ferry . From the ferry , the army moved north to present - day East Falls and went into camp . For the next ten days , the two armies sparred while the British won the Battle of Paoli and several skirmishes . On the night of September 22 , Howe outmaneuvered Washington and won an unopposed crossing of the Schuylkill near Valley Forge . On September 26 , the British army occupied the rebel capital of Philadelphia . In the face of the British advance the Second Continental Congress fled first to Lancaster then to York , Pennsylvania . During the summer of 1777 , Philippe Charles Tronson du Coudray , a French artillery expert , arrived from France . Congress appointed him a major general and inspector general of ordnance , and Washington assigned him the task of strengthening Philadelphia ' s river defenses . His aristocratic airs soon irritated people . He began to quarrel with another French military engineer , Louis Lebègue Duportail , about how the defenses were to be prepared and even managed to anger Gilbert Motier , marquis de La Fayette . To the relief of many , Coudray drowned on September 16 after he foolishly rode his horse onto a Schuylkill ferry and the animal leaped into the river . The Mud Island Fort was designed and begun by British engineer Captain John Montresor in 1771 . The river front was shielded by a stone face , but then the work stopped due to a shortage of money . After the outbreak of war with Britain , the rest of the fort ' s defenses were completed with wooden palisades and earthen ramparts , despite the infighting among the French engineer officers . There were wooden barracks for the enlisted men along the west and north sides of the fort . Nearby was a two - story building to accommodate officers . According to one of the defending soldiers , a battery of 18 - pound artillery pieces stood at the southeast end of Mud Island . On the southwest end , one 32 - pound and four or five 12 - pound and 18 - pound cannons guarded the river . Three 12 - pound guns covered the northwest end of the island . Another account states that ten 18 - pound guns made up the main battery while each of the four blockhouses contained four cannons . A bristling set of sharpened logs surrounded the fort while the low ground along the shoreline was infested with " trous - de - loups " or wolf holes . Chevaux de frise prevented the British navy from ascending the Delaware . Their iron tipped stakes threatened to tear the bottom out of any ship whose master was reckless enough to make the attempt . Siege . Preparations . Colonel Lewis Nicola held Fort Mifflin with a party of Pennsylvania militia , mostly men unfit for field service . Among the approximately 60 militiamen present for duty , not a single one knew how to operate the cannons . On 23 September with Philadelphia about to be captured , Washington sent Lieutenant Colonel Samuel Smith of the 4th Maryland Regiment with a detachment of Continentals into the fort on Mud Island . Smith ' s force numbered 200 soldiers plus Major Robert Ballard of Virginia , Major Simeon Thayer of Rhode Island , and Captain Samuel Treat of the Continental Artillery . However , another account stated that Thayer did not reach Fort Mifflin until October 19 . With the British army closing in on Philadelphia , the small force had to reach Fort Mifflin by a circuitous route . On the last leg of their journey , reinforcements for Mud Island had to be ferried across the Delaware from Red Bank , New Jersey under the protection of the Pennsylvania Navy river flotilla commanded by John Hazelwood . Washington ordered Colonel the Baron Henry Leonard d ' Arendt , a six - foot tall Prussian to take charge of Fort Mifflin . Since the baron was too sick to assume his post , Smith became the effective commander . To further complicate matters , Lieutenant Colonel John Green of the 7th Virginia Regiment , who outranked Smith , arrived with reinforcements on October 18 . Smith developed an uneasy relationship with Hazelwood and their differences soon became obvious . On October 4 , Washington marched against Howe ' s army at the Battle of Germantown but was defeated . To deny the British the use of Province and Carpenter ' s Islands , the Americans broke the riverside dikes . This act forced their enemies to build their batteries on top of the dikes and to labor in knee - deep water . As an example of the difficulties involved , the British lost an 8 - inch howitzer and a soldier drowned when the craft carrying the gun sank in the Schuylkill . On the night of October 10 , Captain John Montresor had his crews begin work on a battery on Carpenter ' s Island , opposite the fort . At this time , the British already had constructed a two gun battery near the mouth of the Schuylkill River . On the 11th , Hazelwood and Smith launched a joint attack by row galleys on the working parties . After losing one man killed and one wounded , a total of two officers and 56 enlisted men from the 1st Grenadier Battalion waved the white flag . The prisoners were quickly herded into the Americans ' boats before engineer Captain James Moncrieffe could arrive with a rescue party of Hessians . The British court martialed two officers for this setback . On October 14 , French engineer Major François - Louis Teissèdre de Fleury came to the fort and proved a great help to Smith . Fleury , who had come to America with Du Coudray , set about improving the defenses . He built a firing step for the soldiers to fire over the palisades , a redan to support the main battery , constructed a last - stand redoubt at the fort ' s center , and corrected some of the fort ' s shortcomings . Thomas Paine visited the fort on the 15th and observed that 30 enemy shells fell into the fort that day . On October 20 , a British red - hot shot set off a minor explosion in the northwest blockhouse . Baron d ' Arendt finally came to assume command on the 21st . While taking the Prussian on a tour of the fort , Smith and Fleury watched with shock and contempt as the terrified man ran away from the damaged blockhouse . D ' Arendt announced that the fort was indefensible and left Mud Island for good on October 27 , pleading " illness " . October 22 – 23 . A Hessian force under Colonel Carl von Donop attacked Fort Mercer on October 22 in the Battle of Red Bank . The 1st Rhode Island Regiment under Colonel Christopher Greene had arrived at the fort only on October 11 after leaving Peekskill , New York on September 29 . Colonel Israel Angell ' s 2nd Rhode Island Regiment reached Red Bank a week later and Major Thayer was sent with 150 soldiers to help garrison Fort Mifflin . When it became clear that the fort was about to be attacked , Thayer and his men recrossed the river to help in Fort Mercer ' s defense . After Donop summoned the fort to surrender twice and each time received a negative response , he resolved to storm the place . The Rhode Islanders waited until their Hessian adversaries reached the abatis and then opened fire . The result was a one - sided slaughter . Greene ' s garrison lost 14 killed , 21 wounded , and one captured while inflicting 90 killed , 227 wounded , and 69 captured on their foes . The Hessians lost a high proportion of officers , including Donop who was mortally wounded . The following day saw another stunning disaster for the British . In support of the assault on Fort Mercer , a squadron from Admiral Howe ' s fleet moved upriver under the command of Captain Francis Reynolds in the ship of the line " HMS Augusta ( 64 ) " . Accompanying the " Augusta " was the sloop " HMS Merlin ( 18 ) " under Commander Samuel Reeve and the frigates " HMS Roebuck ( 44 ) " , Captain Andrew Snape Hamond , " HMS Pearl ( 32 ) " , Captain Wilkinson , and the " HMS Liverpool ( 28 ) " , Captain Henry Bellew . A force of 200 British Grenadiers waited to make an amphibious assault on Mud Island when the fort ' s artillery fire was suppressed . While bombarding Fort Mifflin , the " Augusta " and " Merlin " went aground . High tide came that evening , but contrary winds prevented sufficient depth for the ships to be freed . On October 23 , the American forts concentrated their fire on the two stricken ships . " HMS Isis ( 50 ) " worked its way alongside the stranded sixty - four in a rescue attempt . British accounts claimed that American gunnery did only slight damage but that flaming wads from the ships ' guns caused " Augusta " to catch fire . The Americans asserted that a lucky hit from one of Fort Mifflin ' s red - hot shot or a fire ship started the blaze . An American soldier in the fort wrote that the fire started at the stern of the sixty - four and that the flames spread rapidly . At mid - day , the " Augusta " blew up in a tremendous blast that broke windows in Philadelphia . According to Captain Montresor , 60 sailors , a lieutenant , and the ship ' s chaplain died while struggling in the water . The loud explosion was heard nearly away in Trappe , Pennsylvania . After the destruction of the " Augusta " the crew of the " Merlin " set their ship on fire and abandoned ship . At length the " Merlin " blew up in a less spectacular explosion . Climax . Beginning on October 26 a Nor ' easter struck the area and the storm lasted for three days , bringing with it high winds and torrential rain . With two feet of water over most of Mud Island and similar conditions on Province and Carpenter ' s Islands , the mutual cannon fire stopped as both sides tried to find a dry place . By November 1 , the Americans had the British army in Philadelphia effectively under blockade . Howe ' s troops were short of food , rum , clothing , and money . Montresor complained that he lacked adequate artillery and ammunition . The British were compelled to send supplies into Philadelphia via convoys of flatboats . To avoid being sunk by the guns of Fort Mifflin and the Pennsylvania Navy , the boats had to make the attempt in the night and maintain total silence . Hessian Captain Johann von Ewald noted that in order to hold the sailors to their dangerous work , they were made completely drunk . After a council of war on October 29 , Washington ordered Brigadier General James Mitchell Varnum to assume responsibility for the defense of the Delaware . The two Rhode Island regiments of Varnum ' s brigade were already manning the forts . Soon the last two units of his brigade were committed to the battle . On November 3 , Varnum sent the 4th and 8th Connecticut Regiment s to garrison Fort Mifflin . On November 10 , Montresor was finally prepared to batter down the fort . By that date he had ready for action two 32 - pound , six 24 - pound , and one 18 - pound cannons plus two 8 - inch howitzers , two 8 - inch mortars , and one 13 - inch mortar . On the 10th , the two sides blazed away at each other at a range of . No casualties were suffered by the Americans but large parts of the palisades on the western side of the island were wrecked . On the 11th , Captain Treat was killed by the concussion of a near miss as he talked with Smith . Later that day as Smith was in the barracks , a cannonball smashed through the chimney and struck him in the left hip . Though covered in bricks from the collapsed chimney and suffering from a dislocated wrist , Smith survived because the round was spent . The wounded Smith was ferried across to Red Bank , leaving the garrison leaderless . Varnum reported that the troops would welcome a British infantry assault , but that the constant barrage was taking its toll on the men . Fleury wrote to Washington that all the guns were dismounted except two but that the soldiers of the garrison were able to repair the damage to the palisades every night . The only safe place in the fort was a ditch on the east side and Fleury would go there to round up men for work details , lashing out at the laggards with his cane . The next in command after Smith was Lieutenant Colonel Giles Russell of Connecticut , but he declined and asked to be recalled . On November 12 Major Thayer accepted command of the fort . Sir William Howe began assembling a detachment of light infantry and Foot Guards on November 9 , placing them under the command of Lieutenant Colonel Sir George Osborn , 4th Baronet . These troops were ready by the 13th and were to be supported by the 27th Foot and 29th Foot . By November 14 , the British had planted two additional batteries containing four 32 - pound guns and six 24 - pound guns , which added to the furious daily bombardment . That night Fort Mifflin fired on a supply convoy but missed . The British brought the " HMS Vigilant ( 20 ) " upriver to attack the fort . " Vigilant " was originally the naval transport " Empress of Russia " . She had been converted in June 1777 into a vessel designed for shore bombardment . For this purpose , the ship carried 14 24 - pound cannons , two 9 - pounders , and four 6 - pounders . Before the attack , the British strengthened the vessel ' s sides , added 24 sharpshooters and 50 gunners to the crew , and transferred two extra guns to her starboard side . To maintain the ship ' s stability , water casks were positioned on the port side . Lieutenant John Henry was the commanding officer . Favored by a high tide , the " Vigilant " worked its way into the shallow channel between Mud Island and the north bank at 8 : 00 AM on November 15 . Accompanied by the sloop " Fury " with three 18 - pound guns , the converted transport hurled a barrage at Fort Mifflin from a distance of . Out in the main channel , the " HMS Somerset ( 70 ) " , " Isis " , " Roebuck " , and " Pearl " added the weight of their broadsides from a greater distance . Thayer ordered his 32 - pound cannon to be moved to the place of danger . Before " Vigilant " reached her station , the gun crew claimed to have fired 14 shots into her . After the floating battery came to anchor , the fort was subjected to a terrific point blank fire . A single shot killed five American gunners at one cannon . A defender wrote that men were , " split like fish to be broiled " . Thayer ordered a distress signal to be hoisted requesting help from Hazelwood , but to do so the fort ' s flag had to be lowered first . When the British gunners ceased fire and began to cheer in anticipation of victory , Thayer ' s officers demanded that the flag be immediately raised again . The bombardment resumed and the artillery sergeant detailed to haul the flag was the next casualty , cut in half by a cannonball . That afternoon , a chunk of wood from the smashed barracks struck down artillery Captain James Lee and knocked Fleury unconscious . When Hazelwood ' s ships tried to attack the " Vigilant " and " Fury " , fire from the British naval squadron drove them back . By this time the interior of the fort was furrowed with the tracks of cannonballs and the barracks and blockhouses were wrecked . Osborn planned to send eight flatboats each with 35 soldiers in the first wave of his assault . Howe declined to give the order for the 400 - man storming party to attack , waiting for a high tide and hoping that the garrison would evacuate the fort . That evening , Thayer gave the order to abandon Fort Mifflin . The 300 survivors and what equipment could be salvaged were rowed across to Red Bank . Thayer held back a detail of 40 men . These troops burned down the barracks at midnight and soon joined the others in New Jersey . Thayer was the last to leave . Result . At 6 : 00 AM on the morning of November 16 , the " Vigilant " launched a boat manned by marines to haul down the American flag , which had been left flying . Two hours later , Osborn ' s troops landed amid snow flurries and took possession of the ruined fort . They were greeted by a lone American deserter who told them that Thayer ' s men suffered about 50 killed and 70 to 80 wounded . Historian Mark M . Boatner III estimated total American casualties at 250 from a garrison that counted 450 men plus reinforcements . British losses in the last phase of the siege were seven killed and five wounded . The victors were appalled at the damage and at the blood and brains strewn about the fort ' s interior . While the needy enlisted men were busy looting the corpses for shoes and clothing , a few of the British officers admitted in their letters that the defenders had been brave . Lieutenant General Lord Charles Cornwallis crossed the river with 2 , 000 men . In the face of this threat , Colonel Greene evacuated Fort Mercer and Cornwallis seized the place on November 20 . With the forts gone , Hazelwood set his ships on fire that night to prevent their capture by the British . The Delaware was now open to the Royal Navy and the army of occupation in Philadelphia could be supplied . The next action occurred at the Battle of Gloucester on November 25 as Cornwallis withdrew from New Jersey .