Time Troopers

"Once, military actions were entirely two dimensional, confined to the surface of land and sea, but then submarines and aircraft added a third dimension, vastly extended by spaceflight. Now, consider that if time travel is possible, the fourth dimension of time opens up new possibilities for combat, necessitating new defenses, new strategies and tactics. A battle that was once decisively won might be refought, or a narrow victory might be subtly tilted to the other side. Never mind the history books, they're only works in progress. There might be even more than four dimensions involved, if parallel universes and alternate realities exist and can be accessed. Imagine a universe where Rome never fell and its troops want to do something about our universe, where it did fall. Or another where more recent wars turned out very differently. Battle is a recurrent motif in the Earth of this universe, and would alternate realities be different or all too similar, with the tune the same, but different lyrics. Supplying the lyrics for spacetime combat in these pages is an all-star general staff including Robert Silverberg, Poul Anderson, Fritz Leiber, John C. Wright, H. Beam Piper and more. It's zero hour, in whatever time stream, so grab your time-appropriate weapon, be it sword or ray blaster, buckle on your general issue timeporter belt, and follow the Time Troopers into action across strange aeons!"--