The Brits successfully hid the collection (mostly underground) for over four years.
National gallery
A painting is taken out of storage for routine inspection in 1942 at an underground facility at Manod Quarry, north Wales, where paintings from the National Gallery were moved for safe keeping during wartime.
| Credit: Photo by Fred Ramage/Keystone Features/Hulton Archive/Getty Images

Following the battle of Dunkirk in 1940, as British Prime Minister Winston Churchill grew increasingly concerned about a Nazi invasion on U.K. soil, he ordered that precious works of art from London's National Gallery be evacuated.

After deciding that shipping the paintings to Canada would be too dangerous, politicians and museum authorities housed them instead in a variety of locations in northern Wales, including a disused slate mine. Now, a new exhibit at the National Gallery is exploring how the gargantuan rescue effort took place.

The exhibition, showcasing 24 archival photographs and a new video, shows visitors how the museum successfully hid its art for four years during World War II. It is set to run March 6–April 8.

“Hundreds of feet underground, the Manod slate mine is an extraordinary subterranean space in north Wales. Robin Friend’s photographs convey the wonder of this secret and labyrinthine world, where for four years during the Second World War, the National Gallery hid their collection for safe-keeping," National Gallery curator Minna Moore Ede told The Telegraph.

Museum workers evacuated hundreds of paintings from the London galleries and transported them to the Manod mine in 1940. The entrance to the cave was enlarged with explosives to allow easier transportation for the art, and curators built brick "bungalows" inside the mine to protect the paintings from the damp.

A number of paintings were also transported to the University of North Wales, the National Library of Wales, and three additional Welsh castles, according to the National Gallery website.

The entire collection was fully evacuated by the summer of 1941, the Irish Independent reported.

The British were not the only ones to hide art in caves and castles during WWII. French curators collected and hid art in caves and chateaux during the war, as curator Rose Valland documented the paintings and sculptures looted by the Nazis for retrieval after the war.