blocked the river with two barriers. The first, a mile and a half (2.4 km) below Fort Thompson, consisted of a double row of piles cut off below the water, capped with iron, and backed by a row of 30 torpedoes (present-day mines). Each torpedo contained about 200 pounds (100 kg) of powder. The second was opposite Fort Thompson and consisted of a row of hulks and chevaux de frise, which would force ships to pass under the guns of the fort. Hill hoped that he would be given sufficient manpower to fill his lines, but he was transferred to service in Virginia before the hoped-for additional troops arrived. Shortly after he was succeeded by Brig. Gen. Lawrence O'B. Branch, the district was divided again. Branch's command extended from Cape Lookout north only to the limits of Pamlico Sound. From there to the Virginia border and beyond was assigned to Brig. Gen. Benjamin Huger, whose primary concern was the defense of Norfolk and environs. This meant in particular that Roanoke Island, between Croatan Sound and Roanoke Sound just north of Pamlico Sound, was not included in Branch's command. Roanoke Island fell to a combined operation of the Union Army's Coast Division, under Brig. Gen. Ambrose E. Burnside, and a Union gunboat flotilla assembled from the North Atlantic Blockading Squadron, under Flag Officer Louis M Goldsborough, on February 7–8, 1862. That battle was rapidly followed up by the gunboats alone, who wiped out the Confederate Navy's Mosquito Fleet in an assault on Elizabeth City. Shortly afterward, Goldsborough had to leave the sounds for duties at Hampton Roads, and immediate command of the ships he left behind fell to Commander Stephen C. Rowan. As a result of the battles, Union forces could move at will in Albemarle and Pamlico Sounds. Every city and town accessible to those sounds hence became vulnerable to attack. The most important was New Bern, and Burnside soon resolved to take it. The importance of New Bern was no more obvious to Burnside than it was to the Confederate authorities in Richmond, but they did little to secure it. Although more than a month passed after Roanoke Island fell before Burnside could mount an attack on the city, the local command received no reinforcements. One of General Branch's aides estimated that the lines would need at least 6,130 men to hold them, but he had only about 4,000