The ships having been ordered to cooperate with Count Donop, the Augusta, with four smaller vessels, passed the lower line of chevaux-de-frise, opposite to Billingsport, and lay above it, waiting until the assault should be made on the fort. The flood tide setting in about the time the attack commenced they moved with it up the river. The obstructions sunk in the Delaware had in some degree changed its channel, in consequence of which the Augusta and the Merlin grounded a considerable distance below the second line of chevaux-de-frise, and a strong wind from the north so checked the rising of the tide that these vessels could not be floated by the flood. Their situation, however, was not discerned that evening, as the frigates which were able to approach the fort, and the batteries from the Pennsylvania shore, kept up an incessant fire on the garrison, till night put an end to the cannonade. Early next morning it was recommenced in the hope that, under its cover, the Augusta and the Merlin might be got off. The Americans, on discovering their situation, sent four fire ships against them, but without effect. Meanwhile a warm cannonade took place on both sides, in the course of which the Augusta took fire, and it was found impracticable to extinguish the flames. Most of the men were taken out, the frigates withdrawn, and the Merlin set on fire, after which the Augusta blew up, and a few of the crew were lost in her.

This repulse inspired Congress with flattering hopes for the permanent defense of the posts on the Delaware. That body expressed its high sense of the merits of Colonel Greene, of Rhode Island, who had commanded in Fort Mercer; of Lieutenant-Colonel Smith, of Maryland, who had commanded in Fort Mifflin; and of Commodore Hazlewood, who commanded the galleys; and presented a sword to each of these officers, as a mark of the estimation in which their services were held.

The situation of these forts was far from justifying this confidence of their being defensible. That on Mud Island had been unskillfully constructed and required at least 800 men fully to man the lines. The island is about half a mile long. Fort Mifflin was placed at the lower end, having its principal fortifications in front for the purpose of repelling ships coming up the river. The defenses in the rear consisted only of a ditch and palisade, protected by two blockhouses, the upper story of one of which had been destroyed in the late cannonade. Above the fort were two batteries opposing those constructed by the British on Province and Carpenter's Islands, which were separated from Mud Island only by a narrow passage between 400 and 500 yards wide.

The garrison of Fort Mifflin consisted of only 300 Continental troops, who were worn down with fatigue and incessant watching, under the constant apprehension of being attacked from Province Island, from Philadelphia, and from the ships below.

Having failed in every attempt to draw the militia of New Jersey to the Delaware, Washington determined to strengthen the garrison by further drafts from his army. Three hundred Pennsylvania militia were detached to be divided between the two forts, and a few days afterward General Varnum was ordered, with his brigade, to take a position above Woodbury, near Red Bank, and to relieve and reinforce the garrisons of both forts as far as his strength would permit. Washington hoped that the appearance of so respectable a Continental force might encourage the militia to assemble in greater numbers.

Aware of the advantage to result from a victory over the British army while separated from the fleet, Washington had been uniformly determined to risk much to gain one. He had, therefore, after the battle of Germantown, continued to watch assiduously for an opportunity to attack his enemy once more to advantage. The circumspect caution of General Howe afforded none. After the repulse at Red Bank his measures were slow but certain, and were calculated to insure the possession of the forts without exposing his troops to the hazard of an assault.

In this state of things intelligence was received of the successful termination of the northern campaign, in consequence of which great part of the troops who had been employed against Burgoyne, might be drawn to the aid of the army in Pennsylvania. But Washington had just grounds to apprehend that before these reinforcements could arrive Howe would gain possession of the forts and remove the obstructions to the navigation of the Delaware. This apprehension furnished a strong motive for vigorous attempts to relieve Fort Mifflin. But the relative force of the armies, the difficulty of acting offensively against Philadelphia, and, above all, the reflection that a defeat might disable him from meeting his enemy in the field even after the arrival of the troops expected from the north, determined Washington not to hazard a second attack under existing circumstances.

To expedite the reinforcements for which he waited, Washington dispatched Colonel Hamilton to General Gates, with directions to represent to him the condition of the armies in Pennsylvania, and to urge him, if he contemplated no other service of more importance, immediately to send the regiments of Massachusetts and New Hampshire to aid the army of the middle department. These orders were not peremptory, because it was possible that some other object (as the capture of New York) still more interesting than the expulsion of General Howe from Philadelphia might be contemplated by Gates; and Washington meant not to interfere with the accomplishment of such object.

On reaching General Putnam, Colonel Hamilton found that a considerable part of the northern army had joined that officer, but that Gates had detained four brigades at Albany for an expedition intended to be made in the winter against Ticonderoga. Having made such arrangements with Putnam as he supposed would secure the immediate march of a large body of Continental troops from that station, Colonel Hamilton proceeded to Albany for the purpose of remonstrating with General Gates against retaining so large and valuable a part of the army unemployed at a time when the most imminent danger threatened the vitals of the country. Gates was by no means disposed to part with his troops. He could not believe that an expedition then preparing at New York was designed to reinforce General Howe; and insisted that, should the troops then embarked at that place, instead of proceeding to the Delaware, make a sudden movement up the Hudson, it would be in their power, should Albany be left defenseless, to destroy the valuable arsenal which had been there erected, and the military stores captured with Burgoyne, which had been chiefly deposited in that town.

Having, after repeated remonstrances, obtained an order directing three brigades to the Delaware, Hamilton hastened back to Putnam and found the troops which had been ordered to join Washington, still at Peekskill. The detachment from New York had suggested to Putnam the possibility of taking that place; and he does not appear to have made very great exertions to divest himself of a force he deemed necessary for an object, the accomplishment of which would give so much splendor to his military character. In addition to this circumstance, an opinion had gained ground among the soldiers that their share of service for the campaign had been performed, and that it was time for them to go into winter quarters. Great discontents, too, prevailed concerning their pay, which the government had permitted to be more than six months in arrear; and in Poor's brigade a mutiny broke out in the course of which a soldier who was run through the body by his captain, shot the captain dead before he expired. Colonel Hamilton came in time to borrow money from the Governor, George Clinton, of New York, to put the troops in motion; and they proceeded by brigades to the Delaware. But these several delays retarded their arrival until the contest for the forts on that river was terminated.