In the modern (post-WWII) history of “sea serpent” reports and claims - and there are still reports, albeit rarely - we have only one claim of human fatalities. This story appeared in the May 1965 issue of Fate Magazine and still kicks around in the Internet.
In a first-person account, Edward Brian McCleary claimed to have had a terrifying experience on March 24, 1962 off Pensacola, Florida. McCleary and four friends paddled a life raft out to dive on a wrecked ship. A sudden storm came up, forcing them away from land. At night, a fog closed in on them. In the fog, they hear something moving, and then saw what looked momentarily like a “like a telephone pole about ten feet high with a bulb on top” in the fog. The object was, however, a plesiosaur-like animal. More specifically, “The neck was about 12 feet long, brownish-green and smooth looking. The head was like that of a sea-turtle, except more elongated with teeth. There appeared to be what looked like a dorsal fin when it dove under for the last time. Also, as best I am able to recall, the eyes were green with oval pupils.”
This creature proceeded to kill McCleary’s companions one by one. McCleary alone managed to make it to a protruding mast of the wreck they were diving (the U.S.S. Massachusetts), where he clung until daylight.
The Massachusetts sits today in only 26 feet of water in the Fort Pickens State Aquatic Preserve, with portions of the ship still protruding from the sea. McCleary still lives in Florida, though he apparently has not spoken on the subject of the attack since his article came out. The deaths are real, too, and McCleary did report them, but the Coast Guard found nothing more than a tragic episode of accidental drowning.
What are we to make of this? It's very hard to take seriously even if, as some researchers (myself included) believe, there might still be a huge eel or other creature behind some sea serpent stories, The plesiosaur-like creature striking its victims from the fog sounds like a scene from a bad horror movie. The very plesiosaur-like sketch McCleary made of his creature shows the head joined to the neck at an odd 90-degree angle, and McCleary does not explain by what light he saw enough to describe his creature. So I'm afraid we have to write this tale off. The sea serpent is the most romantic (in the Victorian sense) of legendary creatures, and no one wants to let go of it, but no one can catch hold of it, either. Fortunately, the animals the DO inhabit the oceans are spectacular and curious enough for anyone..
Helm, Thomas. Monsters of the Deep. New York: Dodd, Mead, & Co. 1962. Heuvelmans, Bernard. In the Wake of the Sea-Serpents. New York: Hill & Wang, 1968. McCleary, Edward Brian. “My Escape From a Sea Monster,” FATE, May 1965. Online sources including trueauthority.com, unexplained-mysteries.com, answers.yahoo.com, and (for the Ray Angerman story)