The Big Time. by Fritz Leiber

At the time of the release of this edition of The Big Time, it remains the only Hugo Award-winning work in the public domain. That makes it a very special treasure indeed ! The Big Time tells the tale of a group of service members who work in facilities isolated from regular space-time. They're involved in a war conducted by two shadowy groups that spans time itself, with all of humanity as pawns on an ever-changing historical battlefield.
It explores a fascinating range of themes including time travel, the purpose of war, isolation, and love in the face of it all.