Ragnarok (The Guardian War Book 2). The Guardian War, #2

The war against the Guardians begins with a stunning victory on the lost world of Alkonost. The battle takes heavy toll on Spartan's assault force and leaves him badly wounded and in an induced coma. By the time the battered but victorious fleet reaches the Hellstorm refugee fleet, news has already arrived of their victory against the undefeatable enemy. Inspired by multiple victories, as well as critical information recovered from Alkonost, these once scattered and defeated people are united.
And together they begin their holy war that will wipe away every taint of the Guardians and restore their old empire. The war is a disaster, with dozens of ships lost, and thousands of Humans, Byotai and Trusskans missing in action in the first major engagement. Though not fully recovered from his brutal injuries, Spartan will not rest. He finds his depleted forces are ill-prepared for a rescue operation and are held back by the Trusskans who will not help, but Spartan will not give up.
He has a surprise of his own, a ship that fuses Alliance engineering and Byotai weapons technology into a battlecruiser powerful enough to take on any that stand in his way. A warship built to end worlds. And he will fight against any that stand in his path to save his friends. RAGNAROK is the second book in a brand-new series in the style of Starship Troopers, Aliens and Battlestar Galactica, and set in the bestselling Star Crusades universe.
A unique story that will take the reader to new worlds, and ancient foes never seen before.