In Time for the Rainbow

Using an ancient amulet, Andrei found himself on an alien planet and… in a new body. However, he did not lose his soul, mind, or any of his skills and abilities. The Empire where he found himself is at war and is inexorably yielding ground to an island occupier.
But the previous owner of the body had been a naval commander, and so Andrei is destined to do what he has done all his conscious life — protect those unjustly wronged and restore missing justice. Fear, unknown and bloodthirsty enemies: to your misfortune, the Defender of the Empire is coming.