Mobile Bay was a Union victory. Rear Admiral David G. Farragut’s (North) fleet forced the bay, destroyed the last significant Confederate squadron on the Gulf (Tennessee captured, the gunboats wrecked or taken, Admiral Franklin Buchanan (South) a prisoner), and closed Mobile to blockade-runners. Over the following weeks the forts gave up, squeezed between the fleet inside the bay and Major General Gordon Granger’s (North) troops on the land side. Fort Powell, cut off behind the fleet, had its guns spiked and its magazine blown by Lieutenant Colonel James M. Williams (South) the night after the battle. Fort Gaines surrendered on August 8 under Colonel Charles D. Anderson (South), and the strong one, Fort Morgan, under Brigadier General Richard L. Page (South), held out under bombardment until August 23. The last open Gulf door, east of the Mississippi, was shut.

The port closed, not the city. Mobile the town, miles up the bay, was never attacked in 1864 and held out until April 1865. What happened on August 5 corked the bottle. It did not drink it.

The strategic payoff was large, and the political payoff was larger. Mobile Bay came three months before the November 1864 election, at the lowest ebb of Northern morale. The war was grinding on, the casualty lists were endless, and Abraham Lincoln’s re-election was genuinely in doubt. A war-weary North was within reach of voting in a peace candidate and letting the Confederacy go. Then, in a matter of weeks, the news turned. Farragut took Mobile Bay, and almost immediately William T. Sherman (North) captured Atlanta on September 2. The gloom broke. Historian James McPherson described Mobile Bay and Atlanta together as the first blow of a one-two punch that scattered Northern war-weariness and helped assure Lincoln’s re-election, and with it the war’s continuation to total Union victory and the end of slavery. The fleet action in the bay was also a vote in that election.

The door was a door for something. The Confederacy fought to preserve and extend slavery, and the blockade-runners feeding through Mobile were the supply line of that slaveholding republic. The blockade that strangled them was, concretely, the instrument shutting down the economy of a society built on owning human beings. Emancipation and the blockade were two halves of one policy, and as Union ships took the coast they began taking fugitive slaves aboard and enlisting the men. Closing the port was, in the most literal sense, an attack on slavery. The port was the object. Slavery was the reason.

The clearest proof of that, at Mobile Bay, was who was firing Farragut’s guns. By 1864 the U.S. Navy was a substantially integrated force. Nearly eighteen thousand men of African descent served in it during the war, about a fifth of its entire enlisted strength. In Farragut’s own West Gulf Blockading Squadron the share was lower than in the Navy as a whole, roughly one in five of the enlisted men aboard ship, the smallest proportion of any of the major squadrons. But they were not in the back. They were on the gun decks of the flagship, in the fight.

Two of them, working Hartford’s shell-whip (the rope-and-tackle hoist that lifted heavy gunpowder shells up from the magazine below to the guns on deck), earned the Medal of Honor that day. Landsman John Lawson (North), a landsman being the Navy’s entry rating, the lowest rung, given to a man new to the sea, was a free-born Black sailor from Philadelphia. When an enemy shell struck the berth deck, the crew’s deck just below the guns, it wounded him in the leg and slammed him violently against the side of the ship. He was urged to go below for treatment, refused, and stayed at his post for the rest of the action. Landsman Wilson Brown (North) had been born enslaved on Botany Bay Plantation, near Natchez, Mississippi. A shellburst killed a man on the ladder above him and knocked Brown unconscious into the hold. He came to, climbed back to the shell-whip on the berth deck, and kept the ammunition moving though four of the six men at his station had been killed or wounded. Four African American sailors won the Medal of Honor at Mobile Bay, among an extraordinary number awarded for the battle.

A man born a slave on a Mississippi plantation was, that August morning, hauling shells to the guns of the fleet that was shutting the Confederacy’s last Gulf door. The war’s cause and the war’s instrument stood on the same deck.