Dancers at the Windmill Theatre in London, England practice a routine wearing gas masks and hard-hats with their costumes, 1940. (Photo by Hulton Archive/Getty Images)

Bathing suit models are shown listening to the radio on the beach, circa 1940's. (Photo by Bettmann Archive/Getty Images)

Guests on the terrace of Shepheard's Hotel, Cairo, circa 1940. (Photo by Hulton Archive/Getty Images)

Londoners sleep on the platform and on the train tracks at Aldwych Underground station,London, during heavy all night Nazi bombing raids, October 8, 1940. (Photo by AP Photo)

A soldier of the French Foreign Legion holding his regiment's banner at Bar Hacheim in Libya, circa 1940. (Photo by Three Lions). P.S. All pictures are presented in high resolution.

It is already one of the world’s most iconic cities, but this incredible collection shows how much Paris has changed over the course of the past century. The collection, by French photographer Julien Knez, shows Paris in the 1940s against a backdrop of how the same places look today. Knez says he put the striking collection together to celebrate the 71st anniversary of the city’s liberation from Nazi control in August 1944. Here: Soldiers outside the Hotel De Ville in the 1940s. (Photo by Julien Knez/Caters News)

Back in England, one of the British soldiers that continue to return in their thousands from Northern France, belies any mood of defeat with some high spirited piping on a train. (Photo by Parker/Fox Photos/Getty Images). 1st June 1940

Two female holidaymakers relax on an unidentified beach of England, September 21, 1940, as a soldier, eyes straight ahead, stands guard at a barrier built as a defense against possible invasion by Germany. (Photo by AP Photo)