"Days of Glory" belongs to that unfortunate set of films (e.g., "The North Star", "Our Russian Front", "The Battle of Russia", "The Boy from Stalingrad", "Mission to Moscow", "Song of Russia") that glorified the Russian struggle against the Nazis in World War 2, and then got caught in the political winds of change during the Cold War, and quickly disappeared.
The film takes place in 1941 outside the Russian city of Tula where a group of Russian guerillas prepares for the counterattack against the Nazis. It was based on a story by Melchior Lengyel whose work formed the basis for "Ninotcha" (1939) and "To Be or Not to Be" (1942).
This was the film debut of Gregory Peck (1912-2003) who went on to become a film icon, ranked #12 on the AFI list of Greatest Male Actors. He won an Oscar for "To Kill a Mockingbird" (1962) and was nominated 4 more times ("Twelve O'clock High", "Gentleman's Agreement", "The Yearling", "The Keys of the Kingdom"). He was nominated for an Emmy in 1998 for the TV film "Moby Dick" for which he won the Golden Globe. He had two other Golden Globe nominations ("The Boys from Brazil", "Macarthur").
FWIW - despite all his war films, Peck never served in the military, being classified 4F due to a spinal injury.
This was also the film debut of Russian ballet dancer Tamara Toumanova (1919-96) who plays (guess what?) a Russian ballerina. She made only 7 films including "Torn Curtain" in which she played a Russian ballerina. She married Casey Robinson, the producer on this film.
Husky Alan Reed (1907-77) also made his film debut, as one of the partisans. He's best known as the voice of Fred Flintstone, but he was a busy actor, best known for playing Pancho Villa in "Viva Zapata" (1952).
This was the first film as a producer/writer for Casey Robinson (1903-1979) whose main claim to fame was his 1935 Oscar nomination as the writer of "Captain Blood".
Director Jacques Tourneur (1904-77) is best known for his work on films with Val Lewton, like "Cat People" (1942), "I Walked with a Zombie" (1942), and "The Leopard Man" (1943). In the 50s he transitioned to TV. This was his first big budget film for RKO.
1944 was not a strong year for films. "Going my Way" was the big multiple Oscar winner. "Gaslight" did well at the box office and won Ingrid Bergman an Oscar. Other notable films were Judy Garland's "Meet me in St Louis", "Double Indemnity", "Arsenic and Old Lace". War films were popular - "Lifeboat", "Since You Went Away", "To Have and Have Not", "Hollywood Canteen", "The Fighting Seabees", "Ministry of Fear", "Passage to Marseille", and "The Fighting Sullivans".
The NY Times called the film "artful but daring" and "grim and relentless" but disliked the heavy emphasis on dialogue rather than action, and called Peck's acting "stiff." Indeed Peck himself didn't like his performance and refused to watch the film.
Not only is the action sparse, the special effects are pretty meager. The film is clearly shot on a sound stage and there are very few on location shots.
Bottom line - an OK war film, but if you want to see a better film about the Russian struggle against the Nazis, try "The North Star".