 In 1941, Japanese fighter planes attacked the American naval base at Pearl Harbor, Hawaii, and the United States entered World War II. British codebreakers built Colossus I and II, the world's first programmable, electronic digital computers. The Manhattan Project grew to employ more than 130,000 people and cost close to $2 billion, which is the equivalent to about $26 billion in 2015. Two atomic bombs were produced. One was a simple gun-type fission weapon using uranium-235 called Little Boy, and the other was a more complex, implosion-type weapon using plutonium called Fatman. As part of the Manhattan Project, physicists used the term health physics for the first time as they developed methods to measure radiation being emitted, control radioactive contamination in the workplace, and solve other health-related problems. The term was also used for security purposes because of its vagueness. A term like radiation protection might have aroused suspicion or unwelcome interest by an enemy. However, the term health physics conveyed nothing about Manhattan Project activities. Less than a year after World War II came to an end, President Harry Truman signed the Atomic Energy Act establishing the Atomic Energy Commission to foster and control the peacetime development of atomic science and technology. This act effectively transferred the control of atomic energy from military to civilian hands. Shortly thereafter, an article was published in the Journal of the American Medical Association that described the successful treatment of thyroid cancer using radioactive iodine 131. Due to concerns over fallout from nuclear weapons tests, by the end of the 1940s, the International Commission on Radiological Protection recommended that a radiation dose limit of 1.5 REMs per year be set for the public.