http://www.solpass.org/7ss/standards/MajorEvents.htm
http://www.history.com/shows/wwii-in-hd/videos/world-war-ii-battle-of-stalingrad#world-war-ii-battle-of-stalingrad
http://www.gwu.edu/~nsarchiv/NSAEBB/NSAEBB162/index.htm
http://www.ushmm.org/wlc/en/article.php?ModuleId=10005143