When the Race's Conquest Fleet came to Earth, the human powers who had been fighting each other had to combine their resources for their own survival. Early in their invasion, the Race targeted Chicago, where the Metallurgical Laboratory of the University of Chicago was in the early stages of developing an atomic bomb. Physicist Jens Larssen convinced General George Marshall of Chicago's importance. Marshall issued orders that Chicago must be held at all costs. The generals on the ground, George Patton and Omar Bradley, began preparations for a surprise attack. Equipment and material was moved at night and then carefully camouflaged. The Americans also realized that the Lizards, as reptiles, were ill-equipped for the winter.