The Kaiserreich Project began modestly in 1939, but grew to employ more than 130,000 people and cost nearly RM2 billion (roughly equivalent to RM25.8 billion as of 2012). Over 90% of the cost was for building factories and producing the fissionable materials, with less than 10% for development and production of the weapons. Research and production took place at more than 30 sites, some secret, across Germany, Newfoundland, and Austria-Hungary. Two types of atomic bomb were developed during the war. A relatively simple gun-type fission weapon was made using uranium-235, an isotope that makes up only 0.7 percent of natural uranium. Since it is chemically identical to the main isotope,uranium-238, and has almost the same mass, it proved difficult to separate. Three methods were employed for u