The Atlantic Abomination by John Brunner

Brunner was a very competent science fiction writer but like all novelists, he had to start somewhere. In Brunner's case "somewhere" was "The Atlantic Abomination," a short novel that reads very much like a first effort.
The "abomination" in question is a massive alien life form awakened deep in the ocean. The creature has been hibernating for thousands of years, waiting for the chance to resume his domination of mankind.
It winds up in Jacksonville, Fla. -- of course -- and it is there that a multi-nation team of military men and scientists dig in for battle.
Brunner hated this book and it is a very simple, often silly tale. But it's also an easy read and possesses a certain 50ish Bug Eyed Monster feel that some readers will love.
Also some earlier editions have a wonderful cover showing the title monster being carried across a ravine by a wave of human slaves. It's a knockout cover, much better than the book it advertises.