The Signals Intelligence Service (SIS) was the United States Army codebreaking division, headquartered at Arlington Hall. It was a part of the Signal Corps so secret that outside the office of the Chief Signal officer, it did not officially exist. William Friedman began the division with three "junior cryptanalysts" in April 1930. Their names were Frank Rowlett, Abraham Sinkov, and Solomon Kullback. Before this, all three of them had been mathematics teachers with no cryptanalysis background. Friedman was a geneticist who developed his expertise in cryptology at George Fabyan's Riverbank Laboratories Cipher Department during 1915 to 1917. Besides breaking foreign codes, they were responsible for just about anything to do with the War Department's code systems. The SIS initially worked on a