It isn't really clear why Nazi's reanimated the Dead to create Zombies. It is thought that Group 935 a top secret Nazi Organization that was creating Wonder Weapons and New Technologies for the Reich during the Final Months of WW2. In 1945, while Group 935 was researching and testing Element 115 on Weapons, they found out that Element 115 could reanimate dead cells meaning that could Create an Undead Army which Group 935's leader Dr. Ludvig Maxis wanted. However it didn't really turn out the way he wanted and the Zombies ended up going Berserk all the time. After that the Zombies killed all of the Scientists and an apacolypse began. However Der Riese where the Zombies had taken over was Nuked by the Allies at the end of the war Completely killing them all. Then it wouldn't be until 39 Years later that Element 115 was found Again by Professor Vaulen at the Der Riese site and then took the Samples and back to the Lab. He then tested the Element 115 on his Test Subjects. His Test Subjects were the Head NASA CEO and President. He then Injected them Element 115 into their Bodies and quickly Transformed into Zombies but then during his process he accidently let the Zombies go out of their Chambers. The Professor escaped but The Zombies did too infecting the whole NASA Team at the Cosmodrome creating once again an outbreak.