USS Cairo Sinks: First Warship Destroyed by Mine

A weapon that cost a few dollars destroyed a warship that cost thousands, and naval warfare changed forever. On December 12, 1862, the Union ironclad USS Cairo became the first vessel in history to be sunk by an electrically detonated torpedo, the Civil War-era term for what would later be called a naval mine. The ship went down in the Yazoo River north of Vicksburg, Mississippi, in just twelve minutes. The Cairo was one of seven City-class ironclad gunboats built for the Union's river campaigns on the Mississippi and its tributaries. Constructed in just 100 days at a cost of roughly $100,000, these flat-bottomed, steam-powered vessels carried thirteen guns and two-and-a-half inches of armor plating. They had already proven their worth at Fort Henry and Fort Donelson earlier that year. Commander Thomas O. Selfridge Jr. was leading the Cairo up the Yazoo as part of a joint operation to clear Confederate defenses blocking the approach to Vicksburg. Confederate forces had planted primitive but effective mines in the river, made from five-gallon glass demijohns filled with black powder and triggered by volunteers hidden along the riverbank who pulled insulated wires connected to friction primers. Two explosions struck the Cairo almost simultaneously, ripping holes in the hull below the waterline. The crew abandoned ship without casualties, but the ironclad settled into the muddy river bottom within minutes. Selfridge faced a court of inquiry but was exonerated, as the mines were virtually undetectable. The Cairo lay buried in the Yazoo mud for over a century before being raised in 1964 and eventually restored. The vessel is now displayed at the Vicksburg National Military Park, the only surviving City-class ironclad. The sinking demonstrated that cheap, concealed weapons could neutralize expensive warships, a lesson that would reshape naval strategy through both world wars and beyond.