Frédéric Joliot-Curie
When France was invaded, French nuclear scientist Frédéric Joliot-Curie took charge of the material and hid it in a Banque de France vault and then in a prison. Joliot-Curie moved it to Bordeaux, where it, research papers and most of the scientists (Joliot-Curie remained in France) boarded the British tramp steamer (one of the many merchant ships involved in saving over 200,000 troops and civilians in the three weeks after the Dunkirk evacuation).