Desperate Glory. Morningstar, #4

After a cataclysmic interstellar war that came very close to exterminating humanity, the Daybreak Republic has risen from the ashes and embarked upon a mission to unite hundreds of human colony worlds under its banner, in hopes of preventing a second and final conflict that will complete the destruction of the human race. But not everyone agrees that the empire's ends justify the means. In the aftermath of Leo Morningstar's last mission, war has erupted between the Daybreak Republic and the Secessionist Alliance, stretching the navy's resources to the breaking point.
Admiral Blackthrone's fleet is pinned down, unable to go on the offensive without leaving key worlds exposed, as rebels raid shipping lines and make Daybreak look weak ahead of a major assault. Desperate to break the stalemate before it is too late, Admiral Blackthrone places Leo Morningstar in command of a ragtag fleet of outdated starships and charges him with harassing the enemy, buying time for the navy to assemble the force they need to strike back.
But with resentful subordinates within his fleet and enemy plans finally coming into the light, it may be too late to save the sector - or Daybreak itself.