Warhammer 40k Emperor Expects

"As ork ships lay waste to world after world, heading inexorably towards Terra, Imperial citizens despair. The High Lords become desperate to prove that victory is possible, no matter the cost. A massive Navy fleet is assembled, their mission to make a definitive strike against the orks at Port Sanctus, an area of enemy-held space. But when the Imperial armada arrives, they find themselves outclassed and outmaneuvered; can human courage and faith possibly prevail against such terrible odds?"