Honor and Fidelity - Andrew Keith - Bog

It was an easy assignment on a peaceful alien world-until the natives attacked!
The Sandcastle, on a water world on the fringe of Earth's expanding empire, houses the Fifth Foreign Legion-troops sent there to protect the interests of Seafarms Interstellar, a powerful Terran corporation.
At first, Captain Fraser thought his biggest problem would be keeping the Legionnaires from getting too bored. But that was before the Free Swimmers-the nomadic ocean clans-attacked and nearly overran the Sandcastle.
Suddenly, the Fifth Foreign Legion is facing a seemingly unstoppable alien army equipped not only with their native crossbows, but also high-tech offworld weapons that just might spell the end for the Fifth as well as the Seafarms civilians they have sworn to protect.