Before the 20th century accurate weather information was not available. Military planners had no data on the climate of their target area. In many cases they didn't even have accurate maps of the area. In 1941, when Nazi Germany invaded the Soviet Union they did not have any information on how harsh the Russian winters were. They did not have accurate maps of the roads. Between October 1941 and April 1942 the Germans lost between 100,000 and 112, 000 soldiers to frostbite. That is two-thirds of the number of soldiers who were killed in action or missing.