In this episode we're looking at the attempts to disrupt and destroy Germany's access to heavy water, which was essential for their atomic research.

If that sounds familiar that could be because you've seen the film "The Heroes of Telemark" or watched one of the many documentaries on the operations against the Norsk Hydro plant at Vemork.

I talk to Neal Bascomb, his new book "Winter Fortress" is painstaking researched, with access to the diaries of some of the men involved. It sheds light on a remarkable series of operations in Norway where the weather was as big a threat as the Nazi's