(NewsNation) — UFOs have been in the headlines recently, but some are worried about a different kind of unidentified phenomenon: Unidentified submerged objects.

There have been hundreds of cases of unidentified submerged objects, or USOs. While the idea of mysterious creatures of the seas may call up to mind old beliefs in mermaids or Kraken or modern cryptids like the Loch Ness monster, these phenomena have been identified as a security risk.

With 80% of the world’s oceans unexplored, it’s difficult to scientifically determine what these objects are. Richard Dolan, a UAP historian, has researched more than 600 cases of USOs. It comes with challenges, he told NewsNation.

“Most people are land lovers. We live on land,” Dolan said. “We’re not out in the middle of the water. Unless you live on the shore of an ocean or of a large lake, you’re going to be unlikely to see such water-based phenomenon.”

Dolan identified cases through publically available databases, including those from the National UFO Center and the Mutual UFO Network (MUFON), as well as articles and books.

Around 20% of the cases Dolan researched have had to do with the military. While the Pentagon has not necessarily been responsive, he believes there is no way higher-level officers in the Navy were unaware.

One case from 1971 involved the USS John F. Kennedy aircraft carrier. There was a detailed report from a sailor on that ship who ran communications.

“(OMGHe) described just after they had finished a very intensive period of training called carrier qualifications, they were in the Caribbean and they saw this massive, orange, glowing spherical object that hovered above the ship and, according to what he said, shut down their communications for a good 20 to 25 minutes,” Dolan said.

Some cases, like the 1971 case, involve objects flying in the air before dropping below the surface of the water.

Others, however, were later explained with the discovery of new marine animals. Those include a 1976 incident involving a torpedo recovery boat that was dragging a cargo parachute that got snagged on something. After a fight, the crew pulled a 750-pound, 15-foot-long creature on board.

That creature turned out to be a megamouth shark, which had never been seen before that incident and has only been witnessed 100 times since then.

While some may consider USOs as potentially extraterrestrial in nature, even encounters attributed to earthly creatures can be terrifying in their own right. Take a 1978 case involving the USS Stein, where part of the rubber on the ship’s hull was shredded.

Remnants of claws and teeth were found on the hull, the same kind found in the suction cups of a giant squid. There was just one problem: Previously recovered specimens of the same kind were only a fraction of the size of those found on the Stein.

The size of the claws would indicate a giant squid around 150 long, large enough to consider that perhaps tales of the Kraken might not be so fantastic after all.

The specimen was never recovered. To this day, the largest giant squid ever recorded was just shy of 43 feet long.