Baker's Barn
Baker's Barn is a science fiction - novel by Ady Henry Kissinger in 1996, the action takes place on several levels of time (in the "present" time and in distant future).
content
Initial situation: Humans are waging an interstellar war with two alien races . Mankind vegetates more badly than right on huge platforms in space and is oppressed by an incompetent and corrupt military junta.
A high-ranking general who leads by far the strongest human fighting unit, deserted. He defected to the enemy with his ships and is on his way home (with warlike intent). Those attacked in this way therefore have only one sensible solution: They have to develop a spaceship drive that will bring the other scattered naval units back in time.
To do this, the first-person narrator travels to the earth of the later 20th century and looks there for ways to avert danger.