Battleship Destroyer

Then at 18, after a few too many drinks to celebrate, he was scooped up by the Republic Navy that has not seen a war in generations. A Navy desperate for experianced spacemen to man ships in a loosing war few people even know about yet. Jack realizes that the Battleship fleet he is on is about to be destroyed after he gets a close look at the enemy. But he now knows what drives their ships and powers their weapons and that with equal or even better ships and weapons he now knows how to build, they could win the war.

Thus starts a desperate journey to survive incredible odds long enough to develop or steal the enemies technology. Then test and manufacture the equipment to defeat an enemy that is only known as Spiders becouse of the shap of their ships. The only other thing known about them for sure in the beginning, was that they were slaughtering any human ship and enslaving every system they came across, ignoring all attempts to negotiate.