By 1864, Mobile Bay, Alabama was the most important Confederate port on the Gulf Coast, and an important haven for blockade-runners. Grant included a campaign against Mobile from New Orleans in his master plan for the spring of 1864, but Maj. Gen. Nathaniel P. Banks' debacle in the Red River Campaign prevented it from being carried out by keeping the necessary troops tied up elsewhere. In the summer, plans for the occupation or at least the neutralization of Mobile again were under way, this time as a combined army-navy operation, in which the navy would play the larger role.
Rear Adm. David G. Farragut led a fleet of 18 warships from his Gulf Blockading Squadron in the expedition against Mobile. These included 4 powerful moniters, as well as 14 conventional steam-powered wooden warships such as Farragut's flagship, U.S.S. Hartford. Accompanying Farragut's fleet on transports was a small army force under the command of Maj. Gen. Gordon Granger.
Brig. Gen. Richard L. Page commanded the Confederate defenses of Mobile Bay, which were anchored on 3 forts. Fort Morgan, Page's headquarters, was located on Mobile Point and guarded the main channel into the bay. Fort Gaines lay northwest of Fort Morgan on Dauphin Island, covering the bay's western entrance. Fort Powell, the smallest of the 3, was located still farther northwest on Grant Pass in Mississippi. Supporting the forts was a small Confederate naval flotilla under the command of Adm. Franklin Buchanan. His squadron included the wooden gunboats Morgan, Gaines, and Selma, and the powerful ironclad ram Tennennesse, possibly the most formidable ironclad ever built by the Confederacy.
Confederate obstructions blocked every channel into Mobile Bay except the main passage, so Farragut determined to lead his fleet right past the guns of Fort Morgan. As he had when he ran the batteries of New Orleans and Port Hudson, Farragut had his 14 wooden vessels lashed together in twos, side by side, with the stronger ships on the side facing the fort. The stronger ship in each pair thus protected the weaker ones from the most Confederate fire, and the weaker vessel could help to propel the stronger if its engines should be disabled. On August 5th, Farragut took his fleet into the bay. At the head of his column, the moniter Tecumseh struck a submerged Confederate torpedo and quickly sank with most of its crew. The captain of the next ship in line, the wooden sloop-of-war Brooklyn, backed his engines to avoid a similar fate, throwing the columns in disarry. From his vantage point in Hartford's mizzen shrouds, Farragut shouted , "Damn the torpedoes! Full speed ahead!" and took Hartford into the lead. The other Confederate torpedoes were apparently defective or had become so from their long submergence. Farragut's fleet successfully ran through the channel without further losses.
Once the fleet was inside the bay, it encountered Buchanan's Confederate squadron. Farragut's ships quickly dealt with the 3 wooden Confederate gunboats: capturing Selma, disabling Gaines, and forcing Morgan to flee. Tennessee proved too slow and unwieldy to ram the Union ships and did not have enough firepower to destroy them. Farragut's ships repeatedly rammed Tennessee and poured hudreds of rounds into her until at last, with Buchanan wounded and Tennessee's steering chains shot away, the ironclad surrendered.
The Confederate forts did not last long once Farragut's fleet controlled the bay. The Confederates evacuated Fort Powell on the night of the 5th, and blew it up. Three days later, Fort Gaines surrendered. The next day, Granger's troops began seige operations against Fort Morgan, and on the 23rd, Gen. Page surrendered. Total Union casualties from the summer campaign at Mobile were 327 and Confederate losses were about 1,500 men.