The 288-foot-long Keystone State, luxurious for her day, was the second largest ship on the Great Lakes when she was launched in 1849 and is one of the largest side-wheel steamers to disappear into their depths.

The ship was bound for Milwaukee, Wis., when she left Detroit on Nov. 8, 1861, carrying what was labeled “iron implements,” or farm machinery, on the cargo manifest. Since the sinking, rumors have persisted that the Keystone State was actually carrying military supplies destined for the battlefield.

A cargo of farm machinery in November on a special run — the ship normally moved between Detroit and Buffalo, N.Y. — invites a natural suspicion, Trotter said.

“Farm implements are not heavily used in the winter,” he said.

The nearly 300-foot-long Keystone State was built in Buffalo, N.Y. It had paddle wheels on its sides nearly 40 feet in diameter. The ship was among a class known as palace steamers, according to maritime historian, author and artist Robert McGreevy.

“The interiors were made to look like the finest hotels. They were quite beautiful inside,” he said. “They had leaded glass windows and carved arches and mahogany trim.”

The wheels are both standing. ... It was pretty amazing to see those sitting upright on the bottom like that.

—Diver Martin Lutz