Operation Snatch.

Legend has it that if the famous Barbary Apes leave the Rock of Gibraltar, it's a sign that the British will lose control of it. During World War II, a British officer is put in charge of the apes. When he detects that the animals' morale is slipping, he hatches a plan to go behind the German lines to "kidnap" a new ape for his charges to lift their spirits before the Germans find out about their condition and use it as propaganda.