The Mississippi River rolls through the South as a great avenue of commerce, but its benefits were balanced 150 years ago from the viewpoint of its local inhabitants: The river was the great highway of Union invasion.

With roads poor and railroads easily raided by the South’s defenders, it was water transport that supplied the vast armies of the time. Gens. U.S. Grant and William Tecumseh Sherman helped write new lessons in military history by running fleets of river steamboats past the forts of the South, then launching offensives far from the Union army’s original bases.

And it was often astonishingly small ironclad vessels, by today’s standards, that were thrown together in great haste and then took astonishing poundings from defending artillery. Running the gauntlet of artillery based on the high bluffs of Vicksburg was a particularly intrepid mission for the gunboats of the river.

On Saturday, one of the veterans of the conflict will be on display in a special candlelight tour of the USS Cairo at the Vicksburg National Military Park.

The event commemorates the 150th anniversary of the gunboat’s sinking in the Yazoo River. “Park employees will be dressed in period military uniforms and costume to explain the history of the Cairo and what happened to it,” Will Wilson, park guide and interpreter, told the Vicksburg Post.

The Cairo, one of seven heavily armored gunboats built by Union forces during the Civil War, was engaged in the campaign for Vicksburg — the vital fortress that was the objective of Grant’s great campaign of 1862 and 1863.

Built in Mound City, Ill., the Cairo was scouting up the Yazoo River when it was sunk by an electrically detonated mine — called a torpedo in those days — about seven miles north of Vicksburg on Dec. 12, 1862.

“That was the first time in the United States that an electrically operated torpedo successfully sank a warship,” Wilson said.

The Cairo was raised from the river bottom in 1964 by Operation Cairo, a group of private citizens. It was cut into three sections and repaired at Ingalls Shipyard in Pascagoula.

While the Cairo event will be a particular commemoration of the great Mississippi campaign, the tremendous cost in lives and energy of the war are readily seen in the national and state parks along the river, including Vicksburg and Port Hudson, the two ferociously defended bastions that held out until mid-1863.

The bravery of defenders and besiegers is particularly on display in the ravines and gullies of the Vicksburg battlefield. Some of the assaults launched by Grant, impatient for success and often heedless of the cost in young lives, seem beyond understanding when one is looking at the terrain around Vicksburg. The people of Vicksburg endured shelling and great privations during the long siege.

Those days, particularly now with the 150th anniversary of the great conflict, remain incredible stories that young people can be exposed to at preserved battlefields such as that in Vicksburg. These are truly national treasures that can give insight into the past.