The blockade of Charleston merged into the campaign against the city waged by both the Army and the Navy, not completed until the last days of the war. (See "Raising the Flag at Fort Sumter".) Rather early in the war, the Federal Navy tried to block the harbor entrance by sinking ballast-laden hulks in the channels, but this proved ineffective or worse. Later, ships used in the blockade were used for the abortive assault on Fort Sumter on April 7, 1863. They also provided artillery support for the infantry attacks on Battery Wagner on July 11 and July 18, 1863. After both of these attempts to take the battery failed, the ships remained active in the ensuing siege that eventually resulted in its capture. Then, the Union was able to mount its own guns at the mouth of the harbor, and although the city continued to resist, it was no longer the preferred terminus for blockade runners.