The first attack on Fort Mifflin on 22–23 October had been a disaster with two British ships run aground and burnt. For the second attack three weeks later, Vigilants crew was reinforced with an extra 50 men to work the guns and 24 riflemen to suppress the defenders of the fort during the attack. The ship's sides were reinforced and two guns were transferred to the starboard side of the ship. Her trim was maintained by placing casks of water on the port side. While other ships bombarded the fort from the main channel, Vigilant and a smaller ship worked their way up a secondary channel to the rear of the fort. They were able to silence the fort's guns by 6 p.m., and the Americans evacuated five hours later, despite the ship's grapeshot and small arms fire. During the attack Vigilant only lost three men killed and five wounded; her hull had only been hit several times, but her rigging was shot to pieces. In recognition of the ship's success, her commander, Lieutenant John Henry, was promoted to the command of the frigate .Syrett, pp. 58–59
