Mobile X-ray unit. French soldiers assembled around a mobile X-ray unit during World War I (1914-1918). X-rays had been discovered in 1895 by German physicist Wilhelm Conrad Roentgen, and soon became invaluable for medical diagnostics. When war broke out in 1914, Polish-French physicist Marie Curie worked with the French government to set up 20 mobile X-ray units (called 'petite Curies'). Such units saved the lives of many wounded soldiers. However, the X-ray operators, including Marie and her daughter Irene, were inadequately shielded from the effects of the radiation. Photograph from the Bain News Service, 31 October 1914.