His successor, Major Simeon Thayer, subsequently evacuated the fort on the night of November 15, enabling British troops to occupy the place the following morning.

With Philadelphia effectively blockaded by the Americans, the Howe brothers were forced to lay siege to Fort Mifflin in order to clear the river.

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.

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.

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.

[7] 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.

[6] Colonel Lewis Nicola held Fort Mifflin with a party of Pennsylvania militia, mostly men untrained for field service.

On September 23, 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.

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.

[8] Washington ordered Colonel the Baron Henry Leonard d'Arendt, a six-foot tall Prussian to take charge of Fort Mifflin.

[12] To further complicate matters, Lieutenant Colonel John Green of the 7th Virginia Regiment, who outranked Smith, arrived with reinforcements on October 18.

On the night of October 10, Captain John Montresor had his crews begin work on a battery on Carpenter's Island, opposite the fort.

The prisoners were quickly herded into the Americans' boats before engineer Captain James Moncrieffe could arrive with a rescue party of Hessians.

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.

[20] A Hessian force under Colonel Carl von Donop attacked Fort Mercer on October 22 in the Battle of Red Bank.

[21] 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[22] and Major Thayer was sent with 150 soldiers to help garrison Fort Mifflin.

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).

[24] A force of 200 British Grenadiers waited to make an amphibious assault on Mud Island when the fort's artillery fire was suppressed.

British accounts claimed that American gunnery did only slight damage but that flaming wads from the ships' guns caused Augusta to catch fire.

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.

[30] 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 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.

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.

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.

[50] At 6:00 AM on the morning of November 16, HMS Vigilant launched a boat manned by British marines to haul down the American flag, which had been left flying.

[51] Historian Mark M. Boatner III estimated total American casualties at 250 killed and wounded[7] from a garrison that counted 450 men plus reinforcements.

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.

[53] On November 17, Lieutenant General Lord Charles Cornwallis crossed the river with 2,000 men to prepare for an assault on Fort Mercer.