Philadelphia being lost Washington sought to make its occupation inconvenient and insecure by rendering it inaccessible to the British fleet. With this design works had been erected on a low, marshy island in the Delaware, near the junction of the Schuylkill, which, from the nature of its soil, was called Mud Island. On the opposite shore of Jersey, at Red Bank, a fort had also been constructed which was defended with heavy artillery. In the deep channel between, or under cover of these batteries, several ranges of _chevaux-de-frise_ had been sunk. These were so strong and heavy as to be destructive of any ship which might strike against them, and were sunk in such a depth of water as rendered it equally difficult to weigh them or cut them through; no attempt to raise them, or to open the channel in any manner, could be successful until the command of the shores on both sides should be obtained. Other ranges of _chevaux-de-frise_ had been sunk about three miles lower down the river, and some considerable works were in progress at Billingsport on the Jersey side, which were in such forwardness as to be provided with artillery. These works were further supported by several galleys mounting heavy cannon, together with two floating batteries, a number of armed vessels, and some fire ships. The present relative situation of the armies gave a decisive importance to these works. Cutting off the communication of Howe with his brother's fleet, they prevented his receiving supplies by water. While the American vessels in the river above Fort Mifflin, the name given to the fort on Mud Island, rendered it difficult to forage in Jersey, Washington hoped to render his supplies on the side of Pennsylvania so precarious as to compel him to evacuate Philadelphia. The advantages of this situation were considerably diminished by the capture of the Delaware frigate. The day after Cornwallis entered Philadelphia three batteries were commenced for the purpose of acting against any American ships which might appear before the town. While yet incomplete they were attacked by two frigates, assisted by several galleys and gondolas. The Delaware, being left by the tide while engaged with the battery, grounded and was captured, soon after which the smaller frigate and the other vessels retired under the guns of the fort. This circumstance was the more unfortunate as it gave the British general the command of the ferry, and consequently free access to Jersey, and enabled him to intercept the communication between the forts below and Trenton, from which place the garrisons were to have drawn their military stores.