During WW2 thousands of sites across Britain were requisitioned to support the war effort. Others were built from scratch, regardless of cost. Often their purpose was concealed, even from those living close by and many still exist, albeit with different uses. 

They include underground factories, storage sites and headquarters, spy and communications centre, interrogation & POW camps, research facilities for weapons, treasure stores, even Royal retreats in case of evasion. 

The talk includes several Yorkshire examples. 

The speaker is an author of several 20th century history books and a former head of BBC Yorkshire.