I'm seriously dating myself here.
Sandra Dee and John Gavin (above), who also teamed the same year in Henry Levin's "Tammy, Tell Me True" (also for Universal), play the title characters - he being the son of the Soviet Ambassador to Concordia and she the daughter of his American counterpart. Ustinov essays the role of the leader of Concordia, virtually playing it drunk, and makes a most disarmimg cupid for Romanoff and Juliet.
Ustinov's satire compares favorably with "The Mouse That Roared," Jack Arnold's Cold War satire from the same period, but it inexplicably remains less known than Arnold's film.
The 1958 play which Ustinov wrote and on which his film was based was directed by none-other-than George S. Kaufman and included incidental music by Harold Rome ("Fanny") with lyrics written by Ustinov and ... Anthony Hopkins. Elizabeth Allen played Juliet and Edward Atienza played Romanoff. Ustinov recreated his original Broadway role for the film.
Note in Passing: Speaking of "Tammy, Tell Me True," it is available on DVD in a boxed set from MCA/Universal that includes "Tammy and the Bachelor" (1957) and "Tammy and the Doctor" (1963). I don't know about the other two "Tammys," but I'm a sucker for "Tammy, Tell Me True."