NORTH CHARLESTON, S.C. (AP) — Scientists say a pole on the front of the Confederate submarine H.L. Hunley designed to plant explosives on enemy ships may hold a key clue to its sinking during the Civil War.

The experts are to release their findings Monday at a North Charleston lab where the hand-cranked sub is being preserved and studied. The Hunley was the first submarine in history to sink an enemy warship.

The pole, called a spar, was once placed at the front of the sub and used to plant a powder charge into the Union blockade ship Housatonic in 1864.The Housatonic sank, while the Hunley and its eight-man crew never returned.

The sub was found off South Carolina’s coast in 1995 and raised five years later. It’s been in the laboratory ever since.