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The Arlington Hall effort was comparable in influence to other Anglo-American WW II-era technological efforts, such as the cryptographic work at Bletchley Park, the Naval Communications Annex, development of sophisticated microwave [[radar]] at Massachusetts Institute of Technology's Radiation Lab, and the [[Manhattan Project]]'s development of [[nuclear weapon]]s.

The Arlington Hall effort was comparable in influence to other Anglo-American WW II-era technological efforts, such as the cryptographic work at Bletchley Park, the Naval Communications Annex, development of sophisticated microwave [[radar]] at Massachusetts Institute of Technology's Radiation Lab, and the [[Manhattan Project]]'s development of [[nuclear weapon]]s.

After the [[World War II]], the "Russian Section" at Arlington Hall expanded. Work on diplomatic messages benefited from additional technical personnel and new analysts—among them Samuel Chew, who had focused on Japan, and linguist [[Meredith Gardner]], who had worked on both German and Japanese messages. Chew had considerable success at defining the underlying structure of the coded Russian texts. Gardner and his colleagues began analytically reconstructing the KGB codebooks. Late in 1946, Gardner broke the codebook's "spell table" for encoding English letters. With the solution of this spell table, SIS could read significant portions of messages that included English names and phrases. Gardner soon found himself reading a 1944 message listing prominent atomic scientists, including several with the Manhattan Project.  Efforts to decypher Soviet codes continued under the super secret [[Venona project]].

After the [[World War II]], the "Russian Section" at Arlington Hall expanded. Work on diplomatic messages benefited from additional technical personnel and new analysts—among them Samuel Chew, who had focused on Japan, and linguist [[Meredith Gardner]], who had worked on both German and Japanese messages. Chew had considerable success at defining the underlying structure of the coded Russian texts. Gardner and his colleagues began analytically reconstructing the KGB codebooks. Late in 1946, Gardner broke the codebook's "spell table" for encoding English letters. With the solution of this spell table, SIS could read significant portions of messages that included English names and phrases. Gardner soon found himself reading a 1944 message listing prominent atomic scientists, including several with the Manhattan Project.  Efforts to decipher Soviet codes continued under the super secret [[Venona project]].

Another problem soon arose—that of determining how and to whom to disseminate the extraordinary information Gardner was developing. SIS's reporting procedures did not seem appropriate because the decrypted messages could not even be paraphrased for Arlington Hall's regular intelligence customers without divulging their source. By 1946, SIS knew nothing about the federal grand jury impaneled in Manhattan to probe the espionage and disloyalty charges stemming from [[Elizabeth Bentley]]'s defection and other defectors from Soviet intelligence, so no one in the US Government was aware that evidence against the Soviets was suddenly developing on two adjacent tracks. In late August or early September 1947, the FBI was informed that the Army Security Agency had begun to break into Soviet espionage messages.  

Another problem soon arose—that of determining how and to whom to disseminate the extraordinary information Gardner was developing. SIS's reporting procedures did not seem appropriate because the decrypted messages could not even be paraphrased for Arlington Hall's regular intelligence customers without divulging their source. By 1946, SIS knew nothing about the federal grand jury impaneled in Manhattan to probe the espionage and disloyalty charges stemming from [[Elizabeth Bentley]]'s defection and other defectors from Soviet intelligence, so no one in the US Government was aware that evidence against the Soviets was suddenly developing on two adjacent tracks. In late August or early September 1947, the FBI was informed that the Army Security Agency had begun to break into Soviet espionage messages.