To Brigadier General Duportail
[Englishtown, N.J., 30 June 1778]
You will immediately proceed to Philadelphia, with such of your assistants, as you shall think necessary, to take a full and complete survey of the city the River Delaware and their environs, in order from a collective view of the whole, to form a well-digested plan, for the defence of the River and consequently the city. You are well aware, that in case of an attempt to approach the city by land, the great and almost only security against the success of it will be to have an army equal, or superior in the field, to that, which shall be employed to gain possession of it; and that, if this resource should fail, it would be hardly practicable, by any fortifications on the land side, to prevent the city falling into the hands of the enemy. But as reason and experience prove, that it cannot be held, unless the enemy can have possession of the river and a free communication with their shipping, your principal attention should be directed to the defences of the river. You will therefore have every part of it accurately measured and sounded, the land on the opposite sides, and the Islands in it carefully examined, that you may be able to determine, the best and most effectual means of obstructing the several channels, and raising works to cover and protect those obstructions. The experiment of last campaign points out Mud-Island as a very interesting spot—the trouble, it occasioned the enemy, in so imperfect a state as it was then in, is an argument of its being capable of the most effectual defence if judiciously fortified.
The fort on Mud-Island was reduced by batteries erected on Province Island, and by the enemy’s shipping, which had found out a new channel by way of Hog Island. Province Island is susceptible of being laid under water, and this new channel as well as the others may be obstructed by chevaux de frizes.1
The particulars, I have mentioned, are only intended as hints to assist your enquiries; not meant to direct your judgment. After a thorough examination of every matter necessary to be attended to, you will form your plan on the result and report it to congress and to the commander in Chief.
I have written to General Arnold informing him of the business on which you are sent, and desiring him to afford you all the assistance, in his power, towards accomplishing it.2 Given at Head Quarters English Town June 30th 1778.
Df, in Alexander Hamilton’s writing, DLC:GW; copy, in private hands; copy, PHarH: Records of Pennsylvania’s Revolutionary Governments, 1775–1790; Varick transcript, DLC:GW.