Gregory Peck hated his performance and never saw this film in theaters when it came out.
Although the credits specify all in the credited cast were making their screen debuts, Maria Palmer, Hugo Haas and Tamara Toumanova appeared in movies in earlier years.
Tamara Toumanova spoke so softly that her voice could barely be picked up by the microphones.
The counter-attack described in the film is more or less historical fact. The German Second Panzer Army was stopped in its advance at Tula, south of Moscow. This represented the failure of the initial German attack on the Soviet Union and one of the key turning points of World War II.