Gregory Peck was originally the Sub Captain
I was re-reading a 1967 film mag the other night when I stumbled over a 'gossip page', which said that Gregory Peck was being replaced by Rock Hudson on the movie "Ice Station Zebra". The paragraph mumbled about hasty reshooting because some scenes in Alaska had already been filmed with Peck in them! Mr. Peck moved over to film "The Stalking Moon". There was no explanation why this had happened.
Patrick McGoohan and Gregory Peck! Now that would have been really lipsmackingly good!
http://theatrical-mcgoohan.mysite.orange.co.uk/