Fort Mifflin

Philadelphia, 7 September 1777
... It is evident that from the part which the ennemy have taken of making a descent in Cesepeak bay, the object the least pressing is the defense of the Delaware.
This being supposed, it is clear that the greatest attention ought to be directed to defend as well as possible, the Route which the Enemy have determined upon, by their landing in Chesapeak.
It is certain that fixing on this spot to land [Head of Elk], instead of Mark's hook (which General Gates, Mifflin, and myself thought they would chuse) will encrease considerably the Posts, which in proportion as they advance in the Country, they will be oblig'd to establish to keep up a Communication with their fleet. But the greatest disadvantage attending this, gives not however an entire certainly against the success of their march to Philadelphia, which I always judged and declared, since my arrival here, to be the true object of their Campaign.

To ensure, as much as possible, the success of this Campaign, it is necessary not to be merely contented with securing the Position of Wilmington, where his Excellency has very wisely thought proper to collect his first Efforts.
However strong this position may be supposed by nature, or may be rendered by Art; it appears to me, after what I have heard, that it will be possible for the enemy to pass it on the flank, or perhaps force it; considering especially the small number of Artillery belonging to his Excellency's army.
It appears to me then prudent for Congress to think of providing beforehand for their army, another fortyfied Position, which may secure the army in case they are obliged to abandon the first, and where they may collect new force against an enemy, whom the first success may render more audacious; more especially as Schuylkill is the only considerable river that impedes their March to Philadelphia; and that this River offers at Grays-ferry a Passage which no officer can (I should think) propose to defend.
For this purpose, I offer again my service and that of my officers; in hopes that there will result from it an opportunity of our being in action, which the delay of Congress in pronouncing definitively upon our existence in the service of the United States, always removes at a distance, and which probably we might wait for in vain at the forts on the Delaware; at least before our return in France, should this take place. If the Congress consent to the proposition which I make, to prepare a fortified Camp between Wilmington and Philadelphia, I beg them [First] to communicate this proposition to his Excellency General Washington.
[Second] To give me, as a principal cooperator, General Mifflin, who knows perfectly well this country; who has a very great ascendant over the Inhabitants, by whom the works would be executed and whose great activity and penetration I have had occasion to observe.
[Third] To bring forward, as soon as possible, the remainder of the fifty two pieces brought in the Amphitrite, of which twelve alone are in the northern army, ten, within these few weeks, at the army of his Excellency General Washington; the rest in Springfield, and, at other Places on the east side of Hudson's River.
These thirty remaining pieces of the said fifty two, will be so much the more necessary, as artillery is the foundation of all defensive war; and that of these thirty pieces, there are twenty one which being of a greater length than the others, and even any pieces in the army, are for that reason better for defending the intrenchments ....
-Ford, "Defences of Phila-
delphia," Pennsylvania
Magazine 18:334-37.