Darryl F Zanuck originally announced that this would be directed by James Bond helmer Guy Hamilton, and that James Garner and Oskar Werner would be heading the cast.
This was announced, somewhat fancifully, as being "a sequel" to "The Longest Day", which had given the same studio a bit hit in 1962. Some footage from the earlier film was seemingly used ; it also retains one of the earlier film's Oscar-winning cameramen and its editor, as well as some of the same actors (in different roles).