Prisoner of War by Kevin J. Anderson

Barto is a genetically engineered soldier in a future war. He has body armor, enhanced reflexes, a laser lance as a deadly weapon.

His entire life has been designed for combat, to kill and die on the battlefield, to destroy the Enemy. That is all he knows. 

But when he is cut off from his squadron, freed from the constant drone of commands, he is confronted with the most terrifying crisis—the possibility of peace.