Why would Carol Reed cast Rex Harrison, the most un-sexy actor ever, as the romantic lead against virile Paul Henreid, as the Nazi? I'm sure it had to do with Henreid's slightly Teutonic accent.
Even with Harrison's brittle lack of manly pulchritude, this film is a great classic spy story. Clever banter and self-deprecating English humor thread through the action and suspense. The guns have almost endless bullets and the Nazi always loses.
Despite, the title another mode of transportation steals the limelight in gloriously clever contrivance.
Cary Grant would have been the perfect in Rex Harrison's role. Watch it and see if you don't agree.
Pair this with another 1940 British spy film - Blackout (stars my fav Conrad Veidt (Maj. Strasser) who also was in Casablanca with Paul Henreid (Victor Lazlo))