Secret Messages by David Alvarez

Author:David Alvarez
Language: eng
Format: epub
ISBN: 9780700622900
Publisher: University Press of Kansas
Published: 2017-01-19T16:00:00+00:00

Major Brown emphasized that any schedule should acknowledge that not all traffic can be intercepted and not all intercepted traffic can be read. Referring to McCormack’s interest in traffic between Japan and China, Brown said his stations could probably intercept such traffic if they abandoned other targets whose communications were currently being read, but there was no guarantee that the new traffic could be decrypted. “We could more or less fulfill G-2’s interest in that type of material from an intercept standpoint,” he concluded, “but they would certainly lose everything else that they were now getting.”

Major Telford Taylor, the representative from Special Branch, seconded Major Brown’s concerns, noting that it would be imprudent to divert resources from targets that were currently producing valuable intelligence to attack targets whose intelligence value and powers of resistance were undetermined.5 Eventually such pragmatism won out. In March, Arlington Hall received from army intelligence a new directive that identified the following “Group A” priorities: (1) Japanese army communications; (2) European and African weather traffic; (3) diplomatic communications (including military attaché) between (in rank order) Japan-Russia (Japanese traffic), Japan-Germany (Japanese and German traffic), Japan-Italy (Japanese and Italian traffic), and Japan–Vatican City (Japanese traffic). German military traffic was placed among the secondary targets in “Group B.”6

In its effort to reconcile intelligence needs with the day-to-day realities of intercept and cryptanalysis, the new directive was an improvement over General Kroner’s earlier instructions. Group A traffic was already being collected and processed, so the directive would require the diversion of few, if any, intercept and cryptanalytic resources. The list was heavily weighted toward Japanese targets, a longtime specialty of army sigint. Japanese army systems continued to resist solution, but by the spring of 1943 Tokyo’s military attaché cipher had been solved and, of course, coverage of Japanese diplomatic systems was comprehensive. Most Italian diplomatic traffic was also read. High-grade German diplomatic ciphers remained impenetrable, but Berlin’s diplomatic communications figured only modestly in the Group A schedule. As for the troublesome German army and air force Enigma traffic, it was safely relegated to Group B along with other unproductive targets, such as German and Italian military attaché systems. All in all, the priority schedule played to Arlington Hall’s strengths and required little dislocation in current operations.

The situation changed dramatically in the summer of 1943. In April army codebreakers registered their first success against high-grade Japanese military traffic when they solved the Japanese army’s water transport code, a solution achieved independently by the Central Bureau (Brisbane) and Britain’s Wireless Experimental Center (New Delhi).7 Successes against other Imperial Japanese Army systems followed, and by the end of the year Arlington Hall was scrambling to find the resources to exploit its newfound access to Tokyo’s military communications.

The cryptanalytic units (B Branch) were again reorganized to reflect the new priorities. The division of labor into cipher and code solution was jettisoned in favor of a return to country desks. B-I lost its information and bulletin activities to the headquarters unit and now focused exclusively on the translation of Japanese diplomatic and military messages.

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