How the First Combat Submarine Destroyed a Union Warship, Killed Its Own Crew

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The United States Civil War was the bloodiest conflict in our nation’s history. It was also a period of tremendous advancement in military and weapons technology. Railroads were used for the first time to move vital supplies to manufacturing centers. The first ironclad vessels were built by the North and South respectively, though they used very different designs — USS Monitor had a unique design that ultimately wasn’t carried forward, but it was a “true” ironclad as opposed to the casemate ironclad the South rebuilt, the CSS Virginia (originally called the USS Merrimack). The Confederacy had a fraction of the North’s manufacturing and mining production, but it did achieve a genuine naval first of its own: The first submarine to ever sink another vessel, the H. L. Hunley was built in the South.

For years, only part of the Hunley’s story was known. It was always believed to have been responsible for the sinking of the USS Housatonic in the outer harbor of Charleston, South Carolina, but there was no information on why the vessel had failed to return to shore. The wreck was located in 1995 and raised to the surface in 2000. Since then, scientists have spent nearly two decades researching the vessel and why it never made it back. By the time it deployed to sink the Housatonic, Hunley had actually killed 13 people — five on its first test and the entire crew of eight on its second. A new report suggests that the Hunley‘s successful test run at another vessel was directly responsible for its own destruction.

Hunley1

CSS Hunley

The Hunley was armed with a single explosive charge mounted to the front of the vessel on a long spar. While this is technically referred to as a “spar torpedo,” the better way to think of it is as an enormous fixed charge — a black powder barrel bomb weighing in at ~135 lbs. As scientists examined the wreck, it became clear that something had happened very quickly. All eight crewmen were found at their posts within the craft, and the fore and aft hatches were sealed. The bilge pumps were not set to pump out water and the presence of small stalactites at the top of the boat (it sat on the bottom at a 45′ angle) indicated air had persisted for quite some time. The two holes in the side and bow were determined not to have caused the sinking and occurred after the boat was already on the bottom.

After building a scale model of the Hunley and testing it with various types of shaped charges, loaded with different grain sizes of black powder, the researchers have concluded that the blast pressure from the torpedo detonation likely killed the crew. Remember, the spar torpedo was a huge black powder charge contained within a casing. While black powder isn’t all that explosive compared to modern materials, keeping the charge within a casing let the pressure build until the casing catastrophically failed. The remnants of the spar torpedo were found bent backwards back towards the boat, implying that the explosive pressure was applied uniformly and that the casing had contained the explosion until it catastrophically ruptured. The estimated pressure wave would have been more than strong enough to propagate through the Hunley‘s hull, killing the entire crew.

It’s an interesting explanation for a puzzling situation. The research team dismisses reports that the Hunley signaled a successful attack, pointing out that crews and eyewitness observations are notoriously unreliable in battle. We recently covered a story that postulates the US was fooled into believing its destroyers were under attack in the Gulf of Tonkin because sailors misread the chemical signaling of nearby invertebrate life as evidence that an attack was underway. In the mid-19th century, pressure waves and their propagation through water was not well understood, and the Hunley‘s crew may have been doomed by these gaps in their knowledge. As the report notes: “The H.L. Hunley presents the first documented case of primary blast-induced fatality to personnel within a structure.”

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