The Shadow of War — Timothy S. Johnston

In the world's undersea realms, the superpowers are pressing. Climate change is ravaging the surface nations, and their militaries are surging into the oceans to seek out new resources to sustain their exploding populations. Now Truman McClusky, mayor of the underwater city, Trieste, must gather a team of operatives and travel the world to steal the most unique and deadly weapon ever invented for use underwater. War is looming, and to win a war, one must do whatever it takes, even if it means embracing your darker side.