m, operated by a crank handle on the front panel, was provided for rephasing the receiving distributor whenever this became necessary. The receiving distributor controlled the reinitializing of L-C tank circuits tuned to detect transmitted tones. Because of their high Q, these circuits performed an integrate-and-dump operation during each distributor cycle. This detector was a significant improvement over the prior art, a fact indeed recognized intuitively by ITT, rather than derived from correlation principles. ITT's printer communication system was tested at Rye Lake Airport on February 21, 1945. The printer performed well in the presence of jamming The Historical Origins of Spread-Spectrum Communications 11 dB stronger than the desired signal, and under conditions where voice on the same channel was not intelligble [72]. The interference in this test con- sisted of an AM radio station. Test results of the printer system are men- tioned briefly in a 1946 NDRC Division 15 report [62] which also points out in a radar context that There is factual evidence that tunability is foremost as an AJ measure. Frequency spread of radars, which serves the same function, is a corollary and equally important. [With regard to communications, RF carrier frequency scrambling and time modulation of pulses with time scrambling [are possible communication anti-jam measures]. The report's final recommendations state that "any peacetime program to achieve protection against jamming should not be concerned with the type of equipment already in service, but should be permitted an unrestricted field of development." This was sensible advice to follow, when practical, in the post-war years. An explicit description of an FH system was put forward in early January 1943, when U.S. Army Signal Corps officer Henry P. Hutchinson applied for a patent on FH signaling for "maintaining secrecy of telephone conversa- tions" or for "privately transmitting information" [73]. His scheme employed on-line cryptographic machines to produce a pseudorandom