I am sorry to inform Congress, that the Enemy are now in possession of All the Water defences. Fort Mifflin and that at Red Bank mutually depended on each Other for support, and the reduction of the former made the tenure of the latter extremely precarious, if not impracticable. After the loss of Fort Mifflin, it was found Red Bank could derive no advantages from the Gallies and Armed Vessels (they could not maintain their Station) and in case of Investiture, the Garrison could have no Supplies, no retreat, nor any hope of relief, but such as might arise from a Superior Force acting without on the rear of the Enemy and dislodging them. Under these circumstances, the Garrison was obliged to evacuate it on the night of the 20th Inst., on the approach of Lord Cornwallis, who had crossed the River from Chester with a Detachment, supposed to be about Two Thousand Men and formed a junction with the Troops lately arrived from New York and those that had been landed before at Billingsport. From Genl. Varnum's Account, I have reason to hope, that we saved Most of the Stores, except a few Heavy Cannon, however I cannot be particular in this instance. I am also to add, from the intelligence I have received, that most, if not All the Armed Vessels have been burnt by our own people, except the Gallies, One Brig and Two Sloops, which are said to have run by the City. How far this might be founded in necessity, I am not able to determine; but I suppose it was done under that Idea and an apprehension of their falling into the Enemy's hands, if they attempted to pass up the River. Upon the first information I had of Lord Cornwallis's movement, I detached Genl Huntington's Brigade to join Genl Varnum and as soon as possible Genl. Greene with his division, hoping that these with Glover's Brigade, which was on the march thro' Jersey and which I directed to file off to the left for the same purpose, and with such Militia as could be collected, would be able to defeat the Enemy's design and to preserve the Fort. But they were so rapid in their advance, that our Troops could not form a junction and arrive in time to succour the Garrison, which obliged them to withdraw. Genl Greene is still in Jersey and when Glover's Brigade joins him, if an Attack can be made on Lord Cornwallis with a prospect of success, I am persuaded it will be done. About a Hundred and Seventy of Morgans Corps are also gone to reinforce him. Genls. Poor and Paterson with their Brigades and Colo Bailey with Learned's are now in Camp. The last arrived on Friday Evening. The Other two Genls. Poor and Paterson with their Brigades and Colo Bailey with Learned's are now in Camp. The last arrived on Friday Evening. The Other two in the course of Yesterday. I have not yet obtained Returns of their strength but from the accounts of the Officers, they will amount in the whole to Twenty three or Twenty four Hundred rank and file. But I find many of them are very deficient in the Articles of Shoes, Stockings, Breeches and Blankets. Besides these, about 350 Men, detachments from Lee's Jackson's and Henley's Regiments, have joined me. Yesterday Evening the Enemy burnt several Houses in the Neighbourhood of Philadelphia, and they have committed the most wanton spoil in many Others. I have the honor to be etc.