 Shortly before the outbreak of World War II the paintings were evacuated to various locations in Wales , including Penrhyn Castle and the university colleges of Bangor and Aberystwyth . In 1940 , as the Battle of France raged , a more secure home was sought , and there were discussions about moving the paintings to Canada . This idea was firmly rejected by Winston Churchill , who wrote in a telegram to the director Kenneth Clark , “ bury them in caves or in cellars , but not a picture shall leave these islands ” . Instead a slate quarry at Manod , near Blaenau Ffestiniog in North Wales , was requisitioned for the Gallery 's use . In the seclusion afforded by the paintings ' new location , the Keeper ( and future director ) Martin Davies began to compile scholarly catalogues on the collection , helped by the fact that the Gallery 's library was also stored in the quarry . The move to Manod confirmed the importance of storing paintings at a constant temperature and humidity , something the Gallery 's conservators had long suspected but had hitherto been unable to prove . This eventually resulted in the first air @-@ conditioned gallery opening in 1949 . 
