Cover art
Hogan, James P. The Proteus Operation. Bantam/Spectra 1985.

Hogan, James P. The Proteus Operation
Divergences: 1939 CE, 1926 CE
What if: The Nazis remained an obscure political party or Churchill did not return to the British cabinet after the 1939 German invasion of Poland.
Summary: Beleaguered Americans from 1975 go back in time to prevent Nazi victory in World War II and to promote US atomic weapons research. Unfortunately it's not their own past.
Published: Bantam/Spectra 1985 (0553050958BUY), 1986 (055325698XBUY), 1989 (0553195530BUY); SFBC 1986; Century Hutchinson 1986 (0712695273); Arrow 1987 (0099482002); Baen 1996 (0671877577BUY).
Original in: English.
Translation: German by Edda Petri as Unternehmen Proteus, Heyne 1987 (3453009797).
Translation: Japanese in two volumes as title unknown, Hayakawa 1984 (4150107408, 4150107416).
Translation: Polish by Grzegorz Wozniak as Operacja "Proteusz", Empire 1994.
Translation: Spanish as La operación Proteo, Libros del Atril 2006 (8496575241).
Translation: Spanish as Operación Proteo, Ómicron 2008 (8496575241).
Web link: James P. Hogan's homepage