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I just stumbled across a 6-part series of articles that ran in QST from July to December of 1942.
"Easy Lessons in Cryptanalysis:"
Part of ARRL's efforts to provide some background training for hams who might find themselves doing radio work in the service.
There was also a series of articles starting in April of 1945 about radar. That surprised me a bit, given the early secrecy about radar.
ARRL members can access those issues via the on-line archive.