Jack Williamson's The Legion of Space: The Legion at War

From the back cover: Command the Legion of Space You are Vice Admiral David Ulnar, commanding the Ninth Defense Squadron on the Orion Frontier. You are all that stands between the League of Worlds and the world-wrecking planetoid of Ka'slaq invaders. Now your command will be tested in the most destructive battles ever fought in Jack Williamson's classic tale. Will you outguess the Ka'slaq and block their light-speed attacks - or will their deadly antimatter weapons hold hostage a crippled League of Worlds? Combat Command book #5