In the history of covert-ops weaponry, the “coal torpedo” deployed in the American Civil War stands out as an early example of innovation—or possibly desperation. It was the invention of Thomas Edgeworth Courtenay, a 42-year-old captain in the Confederate Secret Service, who in August 1863 proposed a devious method of sabotaging the Union’s dominance in steam-powered logistics: a gunpowder bomb, deliberately cast to look like a large piece of coal, that Confederate saboteurs could place into coal piles used to fuel Union steamships and locomotives. If the bomb was then shoveled inadvertently into the firebox, the resulting explosion would cause serious damage to the pressurized steam boiler and perhaps even result in a devastating secondary explosion.
Courtenay’s “coal shell” was put into production in Richmond, Virginia, in early 1864. The Union learned of the plan from captured Confederate documents, however, and stepped up security around its coal stores. Northern newspapers referred to the weapon as the “infernal machine” or “coal torpedo.” (In those days the word “torpedo” was applied to many types of weaponry.) The destruction of Confederate intelligence documents late in the war has made it difficult to assess the efficacy of the coal torpedo. Its possible victims include the armed steamboat USS Chenango, the paddle wheel steamer The Greyhound, and the riverboat SS Sultana, though the actual causes of their damage or destruction are open to debate. This ambiguity, of course, might reflect the fact that the bomb was purposely designed to leave little evidence of sabotage.
The bomb’s irregular casing—about 3/8-inch thick—was made of iron or steel. Actual lumps of coal were used to create molds for casting the bombs.
Charge
The explosive charge consisted of 3 to 4 ounces of gunpowder. The inside of each bomb was sanded smooth with emery to reduce the risk of accidental explosions as it was filled.
Filling hole
The filling hole was reinforced in the casting process and threaded to accept a brass plug.
Dimensions
The coal torpedo was about 4 inches across, not so large as to require “trimming” by the fireman. Each bomb weighed 3 to 4 pounds.
Covering
The whole weapon was dipped in a boiling mixture of coal tar, pulverized coal, and resin or beeswax, then plunged into ice water to cool. This process made the bomb look—and smell—like coal.
Chris McNab is a military historian based in the United Kingdom. His most recent book is The Crusades: Holy War, Piety and Politics in Christendom from the First Crusade to the Reconquista (Amber Books, 2019).
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This article appears in the Spring 2020 issue (Vol. 32, No. 3) of MHQ—The Quarterly Journal of Military History with the headline: Weapons Check| Coal Torpedo
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