Murray Leinster 
Creatures of the Abyss [PDF ebook] 
Or, The Listeners

In this gripping action-adventure novel, Murray Leinster turns away from the interplanetary settings that typically form the backdrop of his fiction and instead delves into one of the most mysterious places on Earth: the darkest depths of the sea. Expert radar operator Terry Holt is summoned to an unusual top-secret assignment off the coast of the Philippines. What could be responsible for the strange clues that have been surfacing there?