“Dunkirk” opens as hundreds of thousands of British and Allied troops are surrounded by enemy forces. Trapped on the beach with their backs to the sea they face an impossible situation as the enemy closes in. The story unfolds on land, sea and air. RAF Spitfires engage the enemy in the skies above the Channel, trying to protect the defenseless men below. Meanwhile, hundreds of small boats manned by both military and civilians are mounting a desperate rescue effort, risking their lives in a race against time to save even a fraction of their army.