This is a story I read between 1992 and 1999 about the fight between two opposing human inter-stellar empires that takes place on and in the local vicinity of a relatively back water planet.
It begins with the "enemy" empire invading the planet and one of the inhabitants launching an antique message drone to request assistance from the "good" empire. The good empire receives the drone and sends a defense force. While travelling there they determine that the message drone had been set to jump (go FTL) while still within the planetary atmosphere and that it performed several quick successive jumps on its journey. This discovery leads the fleet commander to reevaluate the standard space combat procedures (used by both sides) since they have modern FTL drives.
Once the good fleet arrives on the scene they dispatch a crack ground team to defend the main settlement. One of the main weapons employed by the ground forces is a needle gun. During the course of the story they wind up getting pinned down and they have to weather an all out assault against superior numbers. They do wind holding out long enough for the space battle to be resolved and reinforcements to arrive.
In space above the planet the good fleet employs new tactics derived from the earlier investigation of the drone to out maneuver and defeat the larger enemy fleet, thus liberating and securing the planet and enabling them to reinforce and support the troops they already had on the ground.
This book may have been part of a larger series but I can't say for sure if it was (I never read any other books in the same universe).
