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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 of 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. 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 an extremely limited budget, lacking the equipment it needed to even intercept messages to practice decrypting.

In 1943, the Army Signal Intelligence Service (later the Army Security Agency) began intercepting Soviet intelligence traffic sent mainly from New York City—assigning the code name VENONA to the project. By 1945, some 200,000 messages had been transcribed, a measure of Soviet activity. On 20 December 1946, Meredith Gardner made the first break into the VENONA code, revealing the existence of Soviet espionage at the Los Alamos National Laboratory.

"After intense study of the Japanese language, I was stationed at Arlington Hall as part of the 2nd Sig Serv Bn. I was given training in cryptography at Vint Hills Farms before the stint at Arlington Hall. We were reading the 1944 Japanese Army General Codebook. There were always glitches, both from faulty reception and failure to break the monthly cyphers. It was our job to fill these in (guess at them) and get the translated messages to McArthur's HQ in the Pacific. We were aided by several two-story barracks filled with IBM computers (then called punch-card tabulators). In January, the new 1945 codebook was published by the Japanese and we were pretty much back to square one. Myself and another expendable Lt. were sent to the Pacific looking for captured code equipment. Our knowledge of what it looked like would supposedly qualify us to find such. No luck on Saipan. 1st Marines did find the code books in the catacombs under Shuri Castle. Back at AH we translated and decryped until one day I got a message with a new word: Genshi Bakudan...atom bomb. War ended. From there it was to Japan to interview civilians and military (USSBS). Then discharge and back to Texas."

• SIGINT