Fort Mifflin Fort Mifflin , originally called Fort Island Battery and also known as Mud Island Fort , was commissioned in 1771 and sits on Mud Island ( or Deep Water Island ) on the Delaware River below Philadelphia , Pennsylvania near Philadelphia International Airport . During the American Revolutionary War , the British Army bombarded and captured the fort as part of their conquest of Philadelphia in autumn 1777 . The United States Army began to rebuild the fort in 1794 and continued to garrison and build on the site through the 19th century . It housed prisoners during the American Civil War . The army decommissioned Fort Mifflin in 1962 and returned it to the City of Philadelphia . Historic preservationists have restored the fort . Colonial defenses of Philadelphia . Upon foundation of Philadelphia in 1681 , people recognized Mud Island near the confluence of the Delaware River and Schuylkill River as strategically important for the defense of the settlement . William Penn , a Quaker with religious objections to military life , however , left Philadelphia undefended . Whenever European colonists established permanent settlements , fortifications in or near those settlements commonly provided protection . Quakers founded the only significant European settlements without fortification . As the Quakers rejected the military , they sought to make peace with the Native Americans in the area to avoid the need for fortifications . While other colonies suffered from conflict and warfare , Philadelphia prospered . By the 1740s , it ranked as the richest British port in the New World . French and Spanish privateer s then entered the Delaware River , threatening the city . During King George ' s War ( 1744 – 1748 ) , Benjamin Franklin raised a militia , because the legislators of the city decided to take no action to defend Philadelphia " either by erecting fortifications or buildings Ships of War " . He raised money to create earthwork defenses and to buy artillery . At the end of the war , commanders disbanded the militia and left derelict the defenses of the city . With renewed colonial warfare in the 1750s , people drew up plans for a fort on Mud Island but did not implement any such plan . Only in the 1770s did the city acquire permanent fortifications . By 1771 , Philadelphia ranked as the largest British port and dockyard in North America . Locals then rose in protest against British economic policies and imports . In response to complaints by the Secretary of State for the Colonies , Philadelphia Governor John Penn asked General Thomas Gage to send someone capable of designing defenses for the city . He intended a fort on Mud Island to help to regulate traffic entering and exiting the port . Gage assigned Engineering Captain John Montresor to the task . Montresor presented six designs to Penn and the Board of Commissioners ; the board proposed constructing a fort on Mud Island ( also known as Deep Water Island ) . The commissioners reviewed the plans , found all too expensive , and insisted on economy despite protestations of Montresor about budget . Montresor stated that his preferred plan cost about £40 , 000 and that he intended to mount " 32 pieces of cannon , 4 mortars and 4 royal howitzers . . . which at 6 men each make 240 men required , 160 musketry , in all 400 garrison . " The colonial General Assembly passed a bill releasing £15 , 000 for the construction of the fort and the purchase of Mud Island from Joseph Galloway , the Speaker of the House . The board instructed Montresor to begin construction but failed to provide him with the funds that he considered necessary to do so properly . The rooms in the farthest interior of " casemate # 11 " probably date from the original construction in 1771 . On 4 June 1772 , Montresor left the head workman in charge of the construction project and returned to New York disgruntled . The project floundered onward for about a year , when it stopped for lack of guidance and funding . The crews completed only the east and south walls , built in stone . History . American Revolutionary War . Following the adoption of the Declaration of Independence , Benjamin Franklin headed a committee to provide for the defense of Philadelphia . The Philadelphia Committee of Public Safety quickly thereafter restarted construction on the fort and finally completed it in 1776 . The committee simultaneously also constructed Fort Mercer , New Jersey , on the eastern bank of the Delaware River across from Fort Mifflin . The Americans intended to use Fort Mifflin and Fort Mercer to control the activity of the British Navy on the Delaware River . Defenders of Philadelphia assembled " chevaux de frise " , obstacles placed in " tiers " spanning the width of the Delaware between Forts Mercer and Mifflin . These defenses comprised wooden - framed " boxes " , 30 feet square , constructed of huge timbers and lined with pine planks . Defenders lowered these frames onto the riverbed and filled each with 20 to 40 tons of stone to anchor it in place . They placed two or three large timbers tipped with iron spikes into each frame , set underwater and facing obliquely downstream . They then chained the boxes together to maintain continuity . The " chevaux de frise " presented a formidable obstacle that could impale unwitting ships . The system design contained gaps to allow passage of friendly shipping . Only a select few patriot navigators knew the locations of safe passage through this barrier . Soldiers at Forts Mercer and Mifflin could fire at anyone attempting to dismantle these obstacles . After the defeat of Washington at the Battle of Brandywine , the British took control of Philadelphia in September 1777 . The British forces then laid siege to Fort Mifflin and Fort Mercer in early October 1777 . The British Army intended the siege to open up its supply line . Captain John Montresor , earlier designer and constructor of early Fort Mifflin , planned and built the siege works used against Fort Mifflin . He then led the siege and destroyed much of Fort Mifflin . During the siege , four hundred American soldiers held off more than two thousand British troops and 250 ships until 10 November 1777 , when the British intensified their assault , launching an incessant barrage of cannonballs into the fort . On 15 November 1777 , the American troops evacuated the fort . Their stand effectively denied the British Navy free use of the Delaware River and allowed the successful repositioning of the Continental Army for the Battle of White Marsh and subsequent withdrawal to Valley Forge . Fort Mifflin experienced the heaviest bombardment of the American Revolutionary War . The siege left 250 of the 406 to 450 men garrisoned at the Fort Mifflin killed or wounded . Comrades - in - arms ferried these dead and wounded to the mainland before the final evacuation . Fort Mifflin never again saw military action . Of the original Fort Mifflin , only the white stone walls of the fort still survive today . The pockmarks in these stone walls evidence the intensity of the British bombardment of 1777 . Local residents know this siege and massive bombardment as the Battle of Mud Island . Reconstruction through War of 1812 . The ruins of Fort Mifflin lay derelict until 1793 . Pierre L ' Enfant , also responsible for planning Washington , D . C . , supervised the reconstruction and designed the rebuild in 1794 under President John Adams . Reconstruction work began on the fort in 1795 under the auspices of Louis de Tousard , who from 1795 to 1800 traveled along the coast between Massachusetts and the Carolinas working on coastal defenses . The army probably built the outer room of " Casemate # 11 " during the reconstruction of the fort from 1794 – 1798 and used it as a " proof room " to make cannon charges . The buildings at Fort Mifflin included barracks for soldiers in the 1790s , measuring by and consisting of two stories . The original barracks contained seven rooms , five of them each designed to house 25 men . The army officially named the fort after Thomas Mifflin in 1795 . Over a cross - shaped hole in the ground previously designated as a last - ditch defensive area near the center of the fort , the army built the extant citadel structure to house the commandant in 1796 . Lieutenant Colonel Stephen Rochefontaine replaced Pierre Charles L ' Enfant as chief engineer at Fort Mifflin in 1798 and completed the citadel structure to house the commandant . Lieutenant Colonel Rochfontaine used but improved original designs of L ' Enfant . The Commandant ' s House exemplifies Greek Revival architecture , rare on Army installations in the United States . The army also built the six cavelike casemate s as defensive structures in the case of an enemy siege during the reconstruction of 1798 - 1801 . Soldiers used a " bake oven " just inside the main gate and the entrance to the bomb - proof casemate for baking bread , as a chapel , and as a mess hall . The army designed the largest casemate ( # 1 ) as a barracks . The three smaller casemates were used for storage . The architects intended Casemate # 5 , about half the size of Casemate # 1 , as the headquarters of Fort Mifflin in the time of attack . The army built the blacksmith shop before 1802 , it is probably the oldest surviving complete structure at Fort Mifflin . ( RG77 NAB ) The army built a two - story officers quarters , measuring by , in 1814 ( # 475 , RG 77 , NAB ) . Pre - Civil War period . The army built a one - story brick structure by in 1815 – 1816 as a guardhouse and prison . Around 1819 , north of the walls of the fort , the army also built a building used as a hospital ( 2nd floor ) and mess hall ( ground floor ) . After the construction of Fort Delaware in 1820 , Fort Mifflin was relegated to secondary status . During the 19th century the area around the fort was drained and filled until Mud Island connected with the western bank of the Delaware River . Nevertheless , the building and garrisoning of Fort Mifflin continued . In the early 1820s , the army began meteorological observations at the fort . The soldiers barracks building was extensively renovated in 1836 , along with the officer ' s quarters . At a later date the soldiers barracks was again renovated , at which time the roofline was changed to add the second floor . ( HABS # PA - 1225E ) . In 1837 the hospital and mess hall building was converted to a meetinghouse ( ASP 7 : 632 ) and an artillery shed , for the storage and protection of cannon , was built on an interior raised platform . By 1839 , the army designated the one - story brick guardhouse - prison as an arsenal . ( Historic American Building Survey ( HABS ) # PA1225 . ) On December 27 , 1842 the army completed a brick , one - story sutler building / storehouse measuring by ( Tompkins to Jessup , Consolidated Correspondence , Box 662 , RG 92 NAB ) . In the 1840s a two - story kitchen wing was added to the officer ' s quarters building . American Civil War . During the Civil War the Union used Fort Mifflin to house Confederate prisoners of war , as well as Union soldiers and civilian prisoners . Numerous Confederate prisoners occupied Fort Mifflin from 1863 to 1865 and were housed in Casemate # 1 . The Union Army used three smaller casemates to hold political prisoners during the same period . Various people wrote graffiti inside the cell doors and on the inner walls of " Casement # 11 " during the 1860s . They also left a wine token and penny , both dated 1864 and in remarkable condition . The Union Army accused William H Howe , one of its soldiers , of desertion , found him guilty of murder , and imprisoned him famously at Fort Mifflin from January 1864 . Howe led an attempted escape of two hundred prisoners from casemate # 5 in February 1864 . Afterwards , Howe was housed in a solitary confinement cell in Casemate # 11 , where he left his signature . Despite his illiterate reputation , Howe twice wrote letters ( filled with bad grammar and run - on sentences ) to President Abraham Lincoln asking for clemency , signing them with his own hand . In April 1864 Howe was transferred to Eastern State Penitentiary then , on 26 August of the same year , was transferred back to Fort Mifflin . The condemned prisoner was briefly held in the fort ' s wooden guardhouse , prior to his execution on the gallows , which were steps away from the guardhouse . Howe ' s hanging was before an audience of persons who paid for tickets to watch the execution . Of the three other men executed at Fort Mifflin , none had a paid public audience . The army proposed adding a sallyport on the west side in 1864 . On 24 November 1864 , the Union Army sent Lieutenant Colonel Seth Eastman , the American Western frontier painter , to Fort Mifflin to supervise the discharge of all civilian and military prisoners , then numbering more than two hundred . On 2 January 1865 , Eastman reported that his garrison consisted of B Company , 186th Pennsylvania Volunteer Regiment , a detachment of recruits , and the hospital staff . After the Civil War . On 20 August 1865 , Captain Thomas E . Merritt with A Company , 7th United States Veteran Volunteers , relieved Lieutenant Colonel Eastman . The army completed West Sallyport by 1866 ( B - 566 , RG 77 , NAB ) . In 1866 , A Company , 7th United States Veteran volunteers , vacated the fort , and the District Engineer Office , Corps of Engineers , replaced the company . The army discontinued the fort as an active post . Between 1866 and 1876 , the Corps of Engineers intermittently repaired and modernized Fort Mifflin and upgraded its armament . The army constructed the detached high battery south of the fort from 1870 to 1875 but never finished it . The army built a torpedo casement in 1874 / 1875 ; its entrance sealed off access to the unused magazine , " Casement # 11 " , preserving a trove of historical artifacts from the light of day . These artifacts include pottery , a tin cup , a tin chamber pot , period buttons , dozens of animal bones . The 1875 Annual Report " The construction of the torpedo casemate has commenced " notes east magazine torpedo casemate . The army constructed this casemate in 1876 . From 1876 to 1884 , the Philadelphia District Office of the Corps of Engineers took custodial responsibility of Fort Mifflin . East Magazine ( torpedo casemate ) first appears on a map in 1886 . ( RG77 , NAB ) The army removed the two story kitchen wings from the officer ' s quarters building sometime before the 1920s ( HABS # PA - 1225F ) . They were restored in the early 1990 ' s in a major restoration of the building . In 1923 the Marine Barracks held the first recorded USMC Birthday dance . Second World War . During the Second World War , the Army stationed anti - aircraft guns at old Fort Mifflin to defend the nearby Fort Mifflin Naval Ammunition Storage Depot ( NASD ) and the United States Philadelphia Naval Shipyard . Marine corps units from Philadelphia Naval Shipyard guarded Naval Ammunition Storage Depot at the northern end of the former Mud and Cabin Islands , while the army assigned troops to the historic fort proper . By 24 April 1942 , the army stationed Battery " H " of the 76th Coast Artillery Regiment , the first Negro Coast Artillery unit in United States history , at the fort . By summer 1942 , the army stationed the 601st Coast Artillery at Fort Mifflin . In 1954 , the fort fell from use as a military post . Several documents reference " old magazine entrance " in the location of " Casement # 11 " , and the number 11 comes from a map legend , dated 1954 and associated with " old magazine entrance " , but the only evidence extant appeared as nothing more than the cap of a chimney . Fort Mifflin closed , ranking among the oldest fort in continuous use in the country . G . E . Brumbaugh renovated the interior of the sutler storehouse in 1960 ; in the 1980s Harold Finigan , then executive director of the fort , renovated its exterior . Decommissioning and restoration . In 1962 , the federal government deeded Fort Mifflin to the City of Philadelphia . In 1969 , Architect John Dickey was responsible for restoring the Blacksmith Shop ' s bellows and forge . In the 1980s ; Harold Finigan , founding executive director of the Fort Mifflin on the Delaware , restored the Blacksmith ' s Building . However Fort Mifflin is still an active base for the United States Army Corp of Engineers ; as a result it is currently the oldest active military base in the United States and the only base in use that pre - dates the Declaration of Independence . In effect Fort Mifflin is the only military base in use that is older than the nation itself . Commandant ' s House was destroyed by an accidental fire started by camping Boy Scouts in the late 1970s . ASP 1 : 11 Architect J . Dickey re - roofed the restored artillery shed in the early 1980s . Harold Finigan , then executive director of the fort , restored the artillery shed and hospital . He also in the 1980s did major restoration of quarters for officers ( including restoration of the kitchen wings ) , arsenal , soldiers barracks , and north and west Sallyports . Harold Finigan restored the arsenal in the early 1990s . He also in 1990s restored barracks of soldiers and the sea wall . Wayne Irby in 2006 rediscovered and unearthed the recently named " Casemate # 11 " at Fort Mifflin . Doctor Don Johnson and a small group of volunteers in August 2006 uncovered and rediscovered the complexity of the inner rooms and the trove of historical artifacts inside " Casemate # 11 " . Standing buildings . Haunted buildings . Apparently , Casemate 11 seems to be the main source of where paranormal activity inside the fort occurs , as well as the Officers ' Quarters and the Blacksmith shop . Many famous ghost hunters have been there , such as Dave Juliano and TAPS from the Syfy show Ghost Hunters and its follow up Ghost Hunters Academy , have declared Fort Mifflin haunted .