Joe Haldeman 
Forever War #1 [PDF ebook] 

A stunning adaptation of the Hugo Award-winning novel.A story of humanity, frailty and the horrors of war.William Mandella, a young physics student has been conscripted into the United Nations Exploratory Force. As a member of an elite task force, he and his comrades are to be sent into the depths of space to battle the alien race that has recently attacked the ships of human columnists.William is witness to the harshest realities of war as training for the mission begins, and he sees that humans have taken on a fight for which they are in no way ready…