Not much is known about the mysterious ships, except they came to rest 4,360 feet, or nearly three-quarters of a mile, below the surface – making them the deepest Gulf or North American shipwrecks to have been investigated.

"What you're going to see and hear I hope will blow your mind. Because it has ours," lead investigator Fritz Hanselmann told reporters. "We went out with a lot of questions and we returned with even more.

"The big question we're all asking is: What is the shipwreck? And the answer is we still don't know," he added.

During eight days of exploration, the scientists used remote-controlled machines to recover more than 60 artifacts from the initial shipwreck site, including musket parts, ceramic cups and dishes, liquor bottles, clothing and even a toothbrush.

The artefacts, including china from Britain, ceramics from Mexico and at least one musket from Canada, will help researchers determine the ships' histories, Hanselmann said.

"Nationalities, cultures, all collide in these shipwrecks. We hope to return in the future next year with more work," he said.

Two of the ships were carrying similar items, and researchers believe they may have been privateers, or armed ships that governments would hire, Hanselmann said.

The third vessel was loaded with hides and large bricks of tallow, suggesting that it may have been a prize seized by the privateers.

The researchers have said it is likely the ships went down during the first two decades of the 1800s, which was a time of great upheaval in the Gulf region and in the New World, in general.

"Empires were falling, Spain was losing its grip, France was selling what it has, Mexico becomes independent, Texas independent, Latin America becomes independent and the US is beginning to make a foothold in the Gulf," he said.

"So these wrecks are all tied to that, we are sure."

Chillingly, it is likely each ship was carrying 50 to 60 men and the researchers believe that none of them survived.

Among the wreckage were telescopes and other navigational tools that survivors likely wouldn't have left behind if they could have helped it, the researchers said.

An anemone living on top of a musket near the wreck