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This monograph reviews events, circa 1920-1960, leading to the development of spread-spectrum communication systems. The WHYN, Hush-Up, BLADES, F9C-A/Rake, CODORAC, and ARC-50 systems are featured, along with a description of the prior art in secure communications, and introductions to other early spread-spectrum communication efforts. References to the available literature from this period are included.
R.A. Scholtz (Sat,) studied this question.