Rent Darling Lili (1970)

Musical superstar Julie Andrews plays Lili Smith, the singing sweetheart who the troops adore. But she has a secret... she's really an enemy agent! And she's just been assigned a new mission: seduce heroic pilot Major William Larrabee (Rock Hudson). The Major can't resist her womanly wiles... but when Lili realises that he has secrets of his own, she begins to wonder which one of them is the true deceiver.