Kraken Island — Eric S. Brown

Colonel Brannon Jackson's Reapers are the toughest, deadliest, black ops squad that America has at her disposal. When the mission can't afford to fail, the Reapers are the ones on the sharp end. A group of doomsday cultists determined to bring about the end of humanity is the Reapers' latest target but this time even the Reapers may not be able to save the world as a prehistoric monster rises to claim the Earth's seas as its own.