In early December 1862, Union forces under the personal command of Maj. Gen. Ulysses S. Grant and Confederate troops led by Lt. Gen. John C. Pemberton eyeballed one another across the Yalobusha River near Grenada.

Back in the Memphis, Maj. Gen. William T. Sherman worked with feverish activity to assemble the requisite river transport to move his Federal soldiers down the Mississippi River against Vicksburg. As the Confederate troops responsible for defense of the Vicksburg-Jackson enclave were pinned by Grant in north Mississippi, Sherman hoped to take advantage of Union naval superiority on the inland waters and make a rapid strike downriver and capture a lightly defended city of Vicksburg.

But the days quickly passed with little to show for Sherman’s efforts as riverboats were tied up in other departments. It was not until Dec. 20 that the red-bearded Sherman was able to embark his command.

But additional Union troops that had been raised in the Old Northwest by Maj. Gen. John A. McClernand, the topic of future columns, arrived in the interim and swelled Sherman’s force by the thousands. Thousands more would be added at Helena, Ark., as Sherman’s Expeditionary Force moved downriver.

To pave the way for a landing by Sherman’s troops, Union naval forces already were active in the vicinity of Vicksburg. Due to the strength of the Vicksburg batteries, Federal operations were focused in the lower Delta, north of the city, where the Yazoo River empties into the Mississippi. (Northern activities afloat on the Yazoo also posed a threat to the vital Confederate Navy Yard at Yazoo City.)

As the South could not compete with the North in terms of ship construction, especially ironclad gunboats, the Confederates used equally revolutionary technology to combat the Union naval presence on the Yazoo River.

Torpedoes, or mines as we would call them today, were placed in the channel of the Yazoo above Chickasaw Bayou. Comprised of a glass demijohn filled with the equivalent of five gallons of black powder these torpedoes were attached to a wooden float, anchored in the channel, and connected by a copper wire to a galvanic cell positioned in a torpedo pit on shore. Should the men manning the torpedo pit spot an enemy vessel, all they need do was press down on the plunger that would send an electric current through the wire to the demijohn and explode the mine.

Although similar devices had been used by the Confederates at Fort Donelson, on the Cumberland River in 1862, they failed to explode, and Federal forces developed an unwise disregard for the “infernal machines.”

All that would change on Dec. 12.

That morning, Lt. Cmdr. Thomas O. Selfridge Jr., was given command of a small flotilla that consisted of his own vessel, the ironclad gunboat Cairo, sister ship Pittsburg and several smaller vessels and ordered to clear the Yazoo channel of torpedoes. As the vessels moved upstream, they soon encountered these strange floating devices in the river. The captains of the smaller vessels in the lead lowered skiffs, and men with cutters and nets attempted to cut the wires and scoop up the torpedoes. Other captains placed riflemen on the bows of their boats to shoot at the torpedoes in hopes of detonating them before they came into proximity of the vessels.

Farther back in line, Cmdr. Selfridge, hearing the firing while aboard the Cairo, feared his flotilla was under attack by Confederate sharpshooters. He immediately sounded “general quarters” and moved his powerful ironclad into the lead. Cairo’s guns were loaded and run out, but no sooner had she pulled into the lead when the gunboat was rocked by two explosions.

Although Selfridge desperately attempted to save his vessel by running her aground, the Cairo quickly sank in six fathoms (about 35 feet) of water and became the first victim in history of an electrically detonated torpedo.

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Next: Federal forces suffer another disaster that derails Grant’s campaign against Vicksburg.

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Terrence J. Winschel is a former historian for the Vicksburg National Military Park.