Why is Howard Hawks 'uncredited'?
Well we all know Hawks directed most of it but I assume it was the same as Poltergeist letting the new boy take the credit?
According to Robert Osburn on TCM, this was Hawks' first sci-fi movie and he did not want his reputation ruined if it was not well received.
Also, Sci-Fi movies were considered a lower class kind of movie and the good/great directors didn't direct them.