The Citadel is a 1938 film directed by King Vidor and starring Robert Donat, Rosalind Russell, Ralph Richardson, Rex Harrison, Francis L. Sullivan, Mary Clare, Cecil Parker and Felix Aylmer. It is based on the A.J. Cronin novel by the same name. I read the book in high school. I prefer another of his books The Keys of the Kingdom, which I read at about the same time.
Yahoo has the film available divided into 13 parts. Part 1:
part 2, part 3, part 4, part 5, part 6, part 7, part 8, part 9, part 10, part 11, part 12, part 13
The New York Times in their review at the time of its release calls it "one of the most satisfying screen dramas of the year." Variety has a review.