Senator Iselin's plane in real life was owned by Frank Sinatra.
The army psychiatrist in this movie was the first black actor cast in a part that wasn't specified as a black character.
The scenes of the convention were filmed at the Old Madison Square Garden on 8th ave at 49th street. The last event ever held there was in Febuary 1968. It was torn down shortly after closing and today an office tower stands on the site.
The topic of the movie was considered politically so highly sensitive it was censored and prohibited just before its theatrical release in many of the former 'Iron Curtain' countries, such as Poland, Czechoslovakia, Hungary, Romania, Bulgaria - and even in neutral countries such as Finland and Sweden. The theatrical premiere for most of those countries was held after the collapse of Soviet Union in 1993.
When Captain Marco is shown a photo of the Communist official Gomel (Reggie Nalder) at a child's birthday party, the two children in the photo are actually the children of screenwriter George Axelrod.