Captured blockade runner USS Calhoun. Source: Naval History and Heritage Command archives.
The first naval engagement at Mobile Bay was an exchange of fire between the Union gunboat USS Huntsville and the Confederate gunboat CSS Florida (not the commerce raider) on Christmas Eve 1861. The Confederate Navy made or attempted to make sorties against the Union blockaders in April 1862 and February 1863.
A second sortie against Ft. Powell by the Union Navy was made on 13 September 1863 by the warships Jackson, Genesee, and the USS Calhoun (a captured blockade runner steamer). The USN gunboats kept up a fire from 10 AM to about 4 PM. Again only a small percentage of the shells fired actually hit the fort or its island. In both engagements no Confederate casualties were caused by the Union Navy gunfire and no damage was done to the fort.
U.S. Navy gunboats USS J.P. Jackson (top) and USS Genesee (bottom). Source: Naval History and Heritage Command archives.