This is a "dog tag" from the civil war.

It was found during the excavation of the Confederate submarine Hunley. The Hunley sank after injecting 90 pounds of explosives into a Union ship that was blockading Charleston, South Carolina.

And this is why archeology is so interesting. What was a union dog tag doing around the neck of a crewman aboard the first sub ever to sink an enemy ship?

It gets better. The tag says "Ezra Chamberlain". Chamberlain was a Union soldier reported dead during a battle near Charleston late 1863. The Hunley did its deed and sank in February, 1864.

So there are many possibilities. The most plausible is that Chamberlain was killed and his tag taken by a Confederate solider. Chamberlain might have asked the soldier to take the tag in a dying wish to let his family know what happened.

Chamberlain might also have become a turncoat and started fighting for the Confederates. Or he might have become a Union spy, put on the sub to scuttle it.

They still don't know why the Hunley sank, so this last possibility is not out of the question.