The Battle of Mobile Bay of August 5, 1864, was a naval and land engagement of the American Civil War in which a Union fleet commanded by Rear Admiral David G. Farragut, assisted by a contingent of soldiers, attacked a smaller Confederate fleet led by Admiral Franklin Buchanan and three forts that guarded the entrance to Mobile Bay: Morgan, Gaines and Powell. Farragut's perhaps apocryphal order of "Damn the torpedoes! Four bells. Captain Drayton, go ahead! Jouett, full speed!" became famous in paraphrase, as "Damn the torpedoes, full speed ahead!"

The battle was marked by Farragut's seemingly-rash but successful run through a minefield that had just claimed one of his ironclad monitors, enabling his fleet to get beyond the range of the shore-based guns. This was followed by a reduction of the Confederate fleet to a single vessel, ironclad CSS Tennessee. Tennessee proceeded to engage the entire Northern fleet. Tennessee's armor enabled her to inflict more injury than she received, but she could not overcome the imbalance in numbers. She was eventually reduced to a motionless hulk and surrendered, ending the battle. With no navy to support them, the three forts also surrendered within days. Complete control of lower Mobile Bay thus passed to the Union forces.

Mobile had been the last important port on the Gulf of Mexico east of the Mississippi River remaining in Confederate possession, so its closure was the final step in completing the blockade in that region. This Union victory, together with the capture of Atlanta, was extensively covered by Union newspapers and was a significant boost for Abraham Lincoln's bid for re-election three months after the battle. This battle concluded as being the last naval engagement in the state of Alabama in the war. It would also be Admiral Farragut's last engagement.

The city of Mobile is situated near the head of Mobile Bay, where a natural harbor is formed by the meeting of the Mobile and Tensaw rivers. The bay is about 33 mi (53 km) long; the lower bay is about 23 mi (37 km) at its greatest width. It is deep enough to accommodate ocean-going vessels in the lower half without dredging; above the mouth of Dog River the water becomes shoal, preventing deep-draft vessels from approaching the city.^{[citation needed]}

The mouth of the bay is marked on the east by a long narrow peninsula of sand, Mobile Point, that separates Bon Secour Bay, where the Bon Secour River enters the larger bay, from the gulf. The point ends at the main channel into Mobile Bay, and here the United States government erected a pre-war fort to shield Mobile from enemy fleets.^{[citation needed]}

Across the entrance, the line of the peninsula is continued in a series of barrier islands, beginning with Dauphin Island. Northwest of Dauphin Island is Little Dauphin Island, then a series of minor islands that are interrupted by a secondary entrance to the bay, Grant's Pass. A few other small islands and shoals lie to the south of Dauphin Island, defining the main channel for as much as 10 mi (16 km) south of the entrance.

Early in the war, the Confederate government decided not to defend its entire coastline, but rather to concentrate its efforts on a few of its most important ports and harbors. Following the loss of New Orleans in April 1862, Mobile became the only major port in the eastern Gulf of Mexico that needed to be defended.

The city subsequently became the center for blockade running on the gulf. Most of the trade between the Confederacy, Havana, and other Caribbean ports passed through Mobile. A few attempts were mounted to break the blockade, but they were not large enough to have lasting impact. Among the most embarrassing episodes of the war for the U.S. Navy was the passage of the raider CSS Florida through the blockade into Mobile Bay on September 4, 1862; this was followed by her later escape through the same blockade on January 15, 1863.