Let’s say you recover a sunken submarine. You’d probably expect to find some evidence of panic, or a last-ditch escape attempt, or anything that shows the people on the sub fought to survive.

But that’s not what the U.S. Navy found when they dredged up the H.S. Hunley.

That’s the mystery behind one of Pop Mech’s most haunting hit stories, “When the Navy Recovered This Sunken Submarine, the Crew Was Dead. Why Were They Just Sitting There?”

The tale begins in the Civil War, with the H.L. Hunley, the first submarine ever to sink an enemy ship. When the Hunley was finally recovered more than a century later, every crew member was still at his post.

Wait, what?

Watch Pop Mech editors Shawn Gorman and John Gilpatrick break down what likely happened inside that cramped iron vessel, and why the very weapon that made history may have killed the crew instantly.

They get into the physics of underwater explosions, the brutal realities of early submarine warfare, and the chilling theory that explains those final moments.

Watch the full episode above now, and find more installments of “The Astounding Pop Mech Show” on PopularMechanics.com.