Bridgehead — David Drake

THERE'S A SECRET
in the basement of the engineering building. Three Travelers, claiming to be from a utopia 6000 years hence, are helping Dr. Gustafson and his graduate staff invent a time transport. Their stated goal--to stop war and save a peaceful future.

Overloaded, overtaxed, the transport experiments start to go wrong. Dreadfully wrong.

What the professors don't know is that the Travelers have their own plans for the machine. And their own secrets:
The future isn't peaceful. The past is not the past.

And the machine in the engineering building has everything to do with an unimaginable war.