Union control of the sea permitted the repeated bombardment of the city, causing vast damage. Although Admiral Du Pont's naval assault on the town's forts in April 1863 failed, the Union navy's blockade shut down most commercial traffic. Over the course of the war, some blockade runners got through but not a single one made it into or out of the Charleston Harbor between August 1863 and March 1864. The early submarine "H.L. Hunley" made a night attack on the on February 17, 1864.