Honor Among Enemies - David Weber

Despite political foes, professional jealousies, and the scandal which drove her into exile, Captain Honor Harrington has been offered a chance to reclaim her career as an officer of the Royal Manticoran Navy. But there's a catch. She must assume command of a squadron of jury-rigged armed merchantmen with crew drawn from the dregs of her service and somehow stop the pirates who have taken advantage of the Havenite War to plunder the Star Kingdom's commerce. Sixth in the bestselling Honor Harrington space war series