Scientists solve mystery of American Civil War submarine

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Explosion of Hunleyhis own torpedo probably killed his crew instantly.

The Hunley in a storage container.
Credit: Friends of the Hunley

Researchers say they solved one of the most enduring mysteries of the American Civil War: What caused the puzzling demise of the HL Hunley, the first combat submarine in history to sink an enemy warship.

The Confederate boat disappeared with all its crew on February 17, 1864, just after destroying the USS Housatonic in Charleston Harbor. The HunleyThe wreckage was not found until 1995. When it was lifted from the seabed in 2000, the skeletons of its eight crew were still at their posts, with no evidence of escape attempts.

Since then, archaeologists and environmentalists have looked into the submarine, which is kept at the Clemson University Restoration Institute in South Carolina, for clues to its destruction. Popular theories have suggested that the crew of the Housatonic managed to shoot holes in the device; that the Hunley accidentally collided with another vessel; or that its crew were neutralized, and possibly killed instantly, by the explosion of the submarine’s own torpedo.

The latter theory now seems correct, says Rachel Lance, a graduate student in injury biomechanics at Duke University in North Carolina. “The pressure wave from the explosion was transmitted to the submarine. He was big enough for the crew to be killed, ”she said.

Lance and other researchers simulated the explosive forces experienced by the crew by detonating a scale model dubbed the USS Tiny, one sixth the size of the Hunley, while submerged in a farmer’s pond. They published their findings on August 23 in PLOS A1.

The Hunley was one of the many first submersibles developed by the Union and Confederate parties during the Civil War, as each side fought for naval supremacy, says James Delgado, former director of maritime heritage at the National Oceanic and Atmospheric Administration of United States. (Delgado is now vice president of a marine archeology company called SEARCH, based in Florida).

The 12-meter-long vessel was constructed from sheets of high-strength boiler iron, held together by rivets hammered flush with its exterior to minimize drag. The crew used gear cranks to propel the craft and leaned over a bench above the center crankshaft. The HunleyThe only weapon was a black copper cylinder filled with gunpowder – ‘about the size of a beer keg,’ Lance says – attached to a 6.7 meter pole mounted on the bow.

In 2013, the theory that the explosion of this cylinder affected the HunleyIts own crew gained credibility when researchers established that the submarine was still attached to the explosive charge when it exploded. They found copper ribbons from the load embedded in the post; suggesting that the torpedo was never intended to be detached from the submarine, but was instead intended to be driven directly into an enemy ship.

To assess the effect of the explosion, Lance and other researchers blew up the Tiny with increasing black powder charges, and used sensors to measure the maximum pressure felt inside the miniature submarine. Lance then used equations to intensify the explosion to match the one that hit the crew of the Hunley, which had a much thinner hull than modern submarines.

Robert Salzar, who studies the biomechanics of blast injury at the University of Virginia in Charlottesville, says the blast could have killed the crew indirectly, knocking them out and sinking the craft, but he doubts the effect was instantaneous. Bleeding and trauma from putting too much pressure on the lungs – a condition called lung blast – is “not instantly fatal in itself,” says Salzar.

Lance says that to be sure of the force of the blast, a full-scale recreation would be needed. She says her findings suggest the crew had a 16% chance of survival, based solely on the lung trauma they likely would have suffered. But she adds that the lack of an autopsy – which should have been performed right after the Hunleyis sinking – makes it impossible to determine a precise cause of death.

By the night of HunleyOn its last mission, the submarine had already sunk twice during training, killing 13 men, including Horace Lawson Hunley, a wealthy lawyer who gave his name and financial backing to the ship.

Yet, says Delgado, perceptions of the craft as a failed experiment are wrong. The submarine was at the forefront of nautical engineering for its time, and its Pyrrhic victory strengthened spirits on the Confederate side after a series of defeats on the battlefield. “There is nothing primitive about Hunley,“, says Delgado.

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Upton, B. Scientists Solve Mystery of American Civil War Submarine.
Nature 548, 511 (2017). https://doi.org/10.1038/nature.2017.22447

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