Gardner's forces at Port Hudson grew in size to approximately 16,000 in March 1863, when Union Rear Admiral David Farragut succeeded in running two of his gunboats past Port Hudson. From this position, Farragut was able to disrupt supplies coming to Port Hudson from the Red River, whose mouth at the Mississippi lay between Port Hudson and Vicksburg. In May 1863, Banks began operations to surround Port Hudson with forces coming both the south and the north. By this time, Gardners' troop strength had been reduced to 7,000, the majority of his forces having been ordered to Vicksburg, where Pemberton was under attack by Union forces under the command of Ulysses S. Grant. On May 22, 1863, Gardner received a command from Johnston, who was odds with Pemberton and Confederate President Jefferson Davis, to evacuate Port Hudson and proceed to Jackson, Mississippi. He was in the process of doing so when word came that 12,000 of Banks's troops had landed north of Port Hudson, while another 20,000 were approaching from the south. Gardner was surrounded, and an escape was impossible. Gardner hence settled in for a long siege. The first assault of the Siege of Port Hudson came on May 27, 1863. The siege lasted 47 days and did not end until July 9, 1863, when Gardner was informed that Vicksburg had fallen on July 4, 1863.