Key Facts
- Duration
- September 26 – November 16, 1777 (≈7 weeks)
- American garrison (peak)
- Never more than 500 men
- Intense bombardment began
- November 10, 1777
- Fort evacuated
- Night of November 15, 1777
- British occupation of Philadelphia
- Held until June 1778
Strategic Narrative Overview
The British opened siege operations against Fort Mifflin while simultaneously attempting to take Fort Mercer. A Hessian assault on Fort Mercer was repulsed with heavy losses at the Battle of Red Bank on October 22, and two British warships grounded near Mud Island were destroyed the next day. After assembling sufficient artillery and naval forces, the British opened an intense bombardment of Fort Mifflin on November 10, steadily silencing the American guns and wounding the fort's commander, Lieutenant Colonel Samuel Smith.
01 / The Origins
Following the British-Hessian capture of Philadelphia on September 26, 1777, General Sir William Howe needed to supply his army by sea. Fort Mifflin on Mud Island and Fort Mercer at Red Bank, reinforced by river obstructions and Commodore John Hazelwood's American flotilla, blocked Royal Navy access to the city via the Delaware River, forcing the Howe brothers to reduce these fortifications before Philadelphia could be sustainably held.
03 / The Outcome
With the garrison unable to return effective fire, Major Simeon Thayer evacuated the surviving defenders by boat to New Jersey on the night of November 15, leaving the flag flying as a ruse. British troops occupied the ruined fort on November 16. Fort Mercer was abandoned shortly afterward, fully opening the Delaware River to British supply ships and securing British control of Philadelphia until their voluntary withdrawal in June 1778.
Belligerents & Mobilization Analysis
Side A
1 belligerent
Captain John Montresor, Vice Admiral Lord Richard Howe, General Sir William Howe.
Side B
1 belligerent
Lieutenant Colonel Samuel Smith, Major Simeon Thayer, Commodore John Hazelwood.
Kinetic Engagement Axis
Scroll horizontally to view full axis. Events plotted relatively.