 During World War II Norway was invaded by Germany and Tronstad conducted domestic resistance for one year before fleeing the country for England. Here, he gathered valuable intelligence from Norwegian sources, both on the development of the V-2 rocket and the growing German interest in heavy water. In 1943 Tronstad planned Operation Gunnerside, in which the German access to heavy water processing at Vemork was severely impeded. His information about the V-2 rocket contributed to the massive Allied bombing of Peenemünde.
