Gehenna Dawn. Portal Wars, #1

Erastus.  An unimaginable nightmare.  A searing hot world, covered with cracked, burning deserts and sweltering jungles.  A hostile planet far from Earth, it was the most hellish place men have ever tried to survive.  Called Gehenna by the condemned men sent to fight there, it forged the few who survived its murderous battles into the strongest soldiers in history. Jake Taylor was a New Hampshire farmboy who wanted nothing more than to marry his girlfriend, work on the farm, and maybe one day write a great novel.
 But mankind was fighting the alien Tegeri and their bio-mechanical cyborg soldiers, and UN Central needed men.men to go to war on hostile worlds like Erastus. Jake wasn't given a choice, not a real one.  He found himself torn from home and family, conscripted for life and shipped to Erastus to take his place in the battle lines, never to return.  In this alien hell, Taylor and his cybernetically-enhanced comrades fight their never-ending war against the servants of the Tegeri, the manufactured soldiers they call simply, the Machines.
Jake survives battle after battle, rising steadily through the ranks, giving all to the desperate fight to save Earth.  But endless combat in hell carries a cost, and Taylor can feel himself losing what little is left of his spirit, his humanity.  When he finally discovers a terrible secret.that everything he'd believed, all he'd fought for his entire life, was nothing but a monstrous lie, he must decide who is the real enemy, and how far he is willing to go to right a horrific wrong.
And if he does what he must to prevail against overwhelming odds and win the final victory, will he be able to control the growing madness inside.or will he be become the very thing he has sworn to destroy?Portal Wars SeriesBook 1:  Gehenna DawnBook 2:  The Ten ThousandBook 3:  Homefront